Engineer's "opinion" on synthetics

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Whilst doing a web search for locally available synthetics, I came across this link. Quite an interesting read, and would be even more interesting to hear what people here have to say about it:
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The following is the response of a GM engine development engineer to a motorcycle forum on extended mileage oil changes. The link to the forum was posted on VV months ago. I found it so interesting I saved a copy. Read with an open mind and form your own opinion about your favorite oil and oil change habits. Only the GM engineer's responses to questions, converted to plain text format, are included. The GM engineers experience and credentials are in the first few sentences of the last paragraph. It's taken special handling to get this long message posted, thanks to vv-help. I've got the entire original in pdf format for those interested. John Dozsa Keep in mind that there are a lot of reasons to change the oil. Oil oxidizes with time and temperature, oil gets contaminated with combustion byproducts, oil gets contaminted with soot from blowby, oil gets contaminated with fuel and water...particularily during cold starts, acids form in the oil, oil gets contaminted with dust/dirt/ debris, the antiwear additive in the oil (the "zinc" or ZDP) gets depleted with engine revolutions, the antioxidants/ anti-acids/detergents/dispesant additive deplete with time and engine revolutions. Synthetic oil addresses the oxidation as it will handle higher temperatures but that is about the only advantage of synthetic...so...in short, using synthetic does NOTHING to allow a longer drain interval. Synthetic has the same amounts of ZDP, same problem with fuel and water contamination, same problems with other contaminates including soot, same problem with acid buildup, etc.... All reasons why synthetic oil does NOT allow longer drain intervals. The water from combustion byproducts/blowby combines with the sulfur in the fuel in blowby to form sulfuric acid over time so oil acidity slowly increases with time and miles and synthetic oil does nothing different to prevent this. You have to change the oil before the anti-acids in the oil additive package are overwhelmed. If oxidation were the only reason to change the oil then synthetics would have an advantage in terms of life or extending the drain intervals. Unfortunately, oxidation due to temperature is RARELY the determining factor for the drain interval so any advantage synthetics might have in this area are moot. I would recommend sticking to the recommended drain intervals even if you use synthetic oil. It is interesting that the new Mobil 1 "extended service" oils added more ZDP to the oil to prevent depletion of the anti-wear additive to market the extended drain intervals to 15,000. BUT....read the bottle. It specifically states that if your engine is under warranty, change the oil at the specified intervals...hmmm....so much for their "guaranteed 15,000 mile interval. Another gem on the bottle is the statement that "if your engine has an oil life monitor follow the oil life monitor and do not use the extended drain interval." The bottle also says that the extended service is void if the engine operates in heavy duty/commercial/livery service, is idled a lot or is operated in a dusty environment. That pretty much eliminates a LOT of other applications and matches the manufacturer's recommendations for sooner oil changes under those conditions. So..after reading the can, exactly what good is the "extended service" Mobil 1. In addition, if youlook carefully, the extended service Mobil 1 does not have the API SG3/SG4 rating as it exceeds the antiwear (zinc) concentration for the API SG3/SG4 ratings. This is not necessarily bad for motorcycles but makes the oil a NON-recommended oil for most modern passenger car applications. I am not making this up....read the fine print on the bottle yourself. I would change the oil at the normal intervals even if you do use a synthetic oil. It isn't MY conclusion...it is a fact. Mobil even says the same thing. They have not stated anything about extended drain intervals with their products until the recent addition of the "extended service -15000" synthetic oil. And they had to modify their existing Mobil 1 product to make that claim (modified to the extent that it doesn't conform to the SG3/SG4 specs anymore) and they STILL put tons of qualifiers on the 15000 claim with the disclaimer about changing it according to the manufacturer's oil life monitor, and changing it sooner if under warranty or operating in towing/commercial service or dusty environments. I am not making that up....read the bottle for yourself. With all the other reasons for changing the oil there is no way that synthetic can claim a longer drain interval. I worked extensively with the GM Research oil chemists that developed the GM Oil Life Monitor and know for a fact that it doesn't change anything in the model for cars with synthetic oil from the factory. I agree that it is possible, under certain conditions, to run the oil past 15,000 or even 20,000 miles in passenger cars with the oil not being "used up" or "worn out"...but...that is assuming no safety factor at all in the oil life and it is under the best of conditions. And...the testing that proved this was NOT synthetic. If the oil is being used under conditions that allow an extremely long change interval then conventional oil will last just as long as synthetic under those conditions. The single advantage of synthetic is it's ability to operate at temps above 305 F without oxidizing rapidly. Since there are few applications where the oil gets that hot the advantage is moot and contributes zero to extended drain capability. Even my CBX with a partial fairing blocking part of the engine never gets the oil to 300 even running on the freeway at 80 in summer weather...I've checked. The fact is that the "extended service" claim for the Mobil 1 15000 oil is a bit hollow...especially when they add several $$$ per quart for the 15000 oil. A modern Cadillac Northstar or LS1 engine will go 12500 miles on the oil life monitor if used in highway driving, best case conditions...and that is validated with conventional, non-synthetic oil !!! So for the extra $$$ for synthetic and extra $$$ for 15000 you only get 2500 extra miles...and Mobil tells you on the bottle NOT to ge 15000 if your car has an oil life monitor. If you saw data showing the oil was fine with extended drain intervals then conventional oil would have done the same thing on that particular test. Forget the idea that synthetic allows longer drain intervals. It is hype by some of the synthetic marketers (primarily Amsoil) to sell/justify their expensive (highly profitable) product. They test under one set of best case conditions and then imply that that is the case for all conditions. The other thing to keep in mind with oil drain intervals is that different engines have distinctly different oil lifes. The life of the oil in the engine is VERY dependent on the engine design, features in the engine and what is expected of the oil. As an example from the engines that I work on, the 93-99 Northstar engine would have a maximum oil life of 7500 miles. This was bumped up to 12,500 miles with the redesign of the engine in 2000 model year. This is the maximum oil life under optimum operating conditions, not the recommended change interval all the time. The difference in the engines is that the 2000 engine has rolling element cam followers instead of direct acting lifters. The rubbing element or direct acting lifters take the antiwear ZDP out of the oil much faster and the direct acting tappets are far more dependent on oil quality and the presence of the ZDP to live. Oil that would be depleted of ZDP in the earlier engines in 7500 miles is still serviceable at 12,500 miles in the newer engines. Older passenger car engines had rubbing element lifters, rubbing element rocker arms, pushrod tips, distributor gears that drove the oil pump, spur gear oil pumps, etc... Those engines needed a lot of antiwear protection and used it up quickly. 3000 mile oil changes on those engines with the oils of the day were probably stretching it under some conditions. Modern engines have gerotor oil pumps, no distributor gears, rolling element everything in the valve gear....they do not chew up the oil nor need high levels of anti-wear additives. Plus, the improved PCV systems keep the oil cleaner. Any oil claims of extended drain intervals that do not make the distinction of what type of service or what type of engine should be highly suspect and considered primarily a marketing ploy. Period. Motorcycle engines, like the FJR, still have rubbing element, direct acting tappets that need lots of ZDP and take the ZDP out of the oil fairly quickly. Synthetic has no advantage nor makes any difference in this respect. In addition, the oil lubricates the gear box where the gear mesh shears down the oil viscosity and takes even more ZDP out of the oil. Wet clutch action contaminates the oil also and is another source of ZDP depletion. Since the basic model for oil life involves the linear depletion of ZDP in the oil due to metal-to-metal contact at lifter interfaces, gear interfaces, etc. I would guess that a motorcycle engine degrades oil life much more rapidly than a car engine...probably twice as fast. Also, motorcycle engines turn twice the RPM of car engines for any given maneuver so that multiplies the oil degradation by 2. The oil life algorithms (that have proven to accurately model engine oil life beyond a shadow of a doubt) actually count engine revolutions to establish the basic oil decay rate...so...the more revolutions the greater the degradation. This linear decay rate is multiplied by various factors that account for the oil operating temperature, ambient conditions, soak times, run times, engine load and many others. Short trips in cold weather will add considerable deterioration because of the effects of contamination by gas and water. Since cold weather operation is not much of a factor with bikes and they do tend to get thoroughly warmed up each ride (most people don't "housewife" a bike on short trips and many stops) I would guess that the main factor in oil life with bikes is the depeletion of the antiwear additives....which would be the same with synthetics or conventional oil. Understand, also, that any modern oil that meets the SL or SM API performance requirements have quite a bit of synthetic content in them. Any multivis oil that meets SM performance specs must have a synthetic polymer Viscosity Improver package or it wouldn't pass. So, any modern oil is a synthetic "blend" as some companies like to market and charge extra for....LOL. Amsoil.....????.....That is an oil marketing company that utilizes a pyramid scheme to sell their product thru a system of distributors and dealers and such. They know absolutely nothing more about oil than Mobil or Texaco or the other major oil manufacturers. Their bogus claims are meant to sell their products at high prices to benefit their pyramid marketing scheme. How could they justify the high price they charge for their product otherwise. Their products probably perform well to some extent but they have no outstanding attributes that others do not have for half the cost. Their claims of long change intervals are completely nonsense. They base them on the lower oxidation rates of their synthetic products at high operating temps. As mentioned, that is rarely, if ever, the defining factor in oil changes and the testing that determines the oxidation rates is run at temps above what most engines will ever operate at. They take something completely out of context and pretend that it is a big advantage. It isn't. If you look at all the tests that oils must pass to meet the API standards for performance, Amsoil only quotes selected results in areas of testing that do not replicate normal engine operation. If you really understand ALL the things that govern oil life Amsoil's claims evaporate. They make themselves sound very technical and quote lots of "data" but it is a smokescreen to cover their marketing scheme that benefits their distributors and dealers..... First, though, let me be clear. Synthetics, such as Mibil 1, are excellent products. They can survive at temperatures well above the oxidation limits of conventional oil of 305 F. If an engine operates at those oil temperatures then synthetic is applicable. Synthetic offers good low temperature viscosity and pour points... low meaning below -40. Down to the -30/-40 range conventional oils are fine. If you are searching for oil on the northslope and cold start regularily at -40 then consider synthetic. Other than that, synthetic oil's usefulness is questionable in passenger cars. Racing teams use synthetic oil for several reasons. First and foremost is marketing. If it is "good for racing" then it must be great stuff, right??? Fooled you , didn't it..!!! LOL LOL The racing teams get paid lots of sponsorship $$$$ to run the oils and put the stickers on the cars. That is why they use it. If someone paid them enougth money to run lard in the motors they probably would. The engines will run fine with conventional oils as evidenced by teams sponsored by conventional oil companies that do not run synthetic. In racing things happen to often drive the oil temps above 305 F. If this happens....the synthetic can take it and conventional oil would have a limited life. It lets the NASCAR boys tape over the oil cooler for better aero during qualifying and if the oil creeps to 350 in the process there is no harm done. So it has a marginal use and is a good insurance policy for when the going gets rough and that fender gets pushed in an blocks off the oil cooler. There are a number of new cars that specify Mobil 1. I work specifically on several of them. The Corvette LS1 is spec'ed a synthetic oil engine and the RWD Northstar engines in the SRX/STS/XLR are also factory filled with Mobil 1. So will be the supercharged Northstar in the STS-V/XLR-V. Why you ask?? One simple reason. There is no need to put an oil cooler on the car if it has synthetic oil in it. If the owner takes it to a track day and runs the car on the track hard the oil will get over 305 without an oil cooler. Synthetic oil will take it and conventional oil would be questionable. Otherwise, the performance cars like this would all need large oil coolers and all the associated plumbing. Putting all that extra equipment on all cars so that the 2% that actuallly see the track will keep the oil cool is not a good idea. Better to leave off the cooler (less expense, less chance of oil leaks, less complexity, less to maintain with age) and protect the small percentage of engines that might get the oil above 305 with the synthetic. Regardless of what you have read, were told or believe this is the main reason that factory cars are spec'd for synthetic. Period. I know because I work with them everyday and can assure you that that is the truth. Interestingly, the real hotrods, like the STS-V run oil coolers AND synthetics because the engine will push the oil temp over 305 even with a large cooler if used for continuous track work. So, even though the car has an oil cooler, the same logic and reasoning applies...use the synthetic to keep from having to put a HUGE oil cooler on it. The engine oil temp does not run any cooler with the synthetic, by the way. I have run lots of engine cooling tests with conventional and synthetic oils and the oil temp is the same regardless...just that the synthetic has highe oxidation temps. If an engine is designated for factory fill with synthetic it has other uses as well. In the case of the Northstar engines in the STS/SRX/XLR the engine has variable valve/cam timing (VVT) on all four cams. The VVT system uses engine oil pressure as a hydraulic system to move the cam phasers using control signals from the PCM. The VVT system is a hydraulic circuit that is separate from the normal engine lube circuits. In cold start situations the viscosity of the "hydraulic oil" must reace a certain level before the VVT system will respond quickly enough to allow it to be used. The more linear cold viscosity of the synthetic products allow earlier application of the VVT on cold starts. Without the synthetic the system would still work fine...just the cam phasers would "park" until the engine oil reache a certain temperature. Since the synthetic was spec'd anyway, it is exploited in the engine design to be able to better utilize the VVT system. So.....that is why factory cars have synthetic. Not because it is magic or has better "wear" properties...just because it can live above 305 for extended periods of time. Interestingly, the synthetic only adds about 25 degrees of increased oil temp range above 305. The metal parts in the engine, that are much hotter than the oil and that are cooled by the oil, cannot take much higher temperatures. Aluminum starts to loose strength and gets "soft" enough that it will start to collapse in structural areas. Even hardened steel , like tappet faces, start to temper and soften at temps approaching 375/400F so if the oil is starting to approach 330 or so the tappet faces are getting periously close to the range that they will be starting to temper and anneal. Not desireable. In a race engine that will be torn down after the race and wear parts replaced this is not such a stringent condition but in a passenger car or street bike engine those temps cannot be seen without damage.....so.....the high temp capability of the synthetic oil cannot really be exploited by much. As an aside, you will find that "racing" has little to do with passenger cars or street bike engines. Just because something works on racing cars or is used by racing teams does not mean it is good or applicable to everyday use on the street. The marketers like to make you THINK that racing means good but that is just marketing and an image. Look at the facts, first. Like I said, the synthetics are excellent products. You certainly are not going to hurt anything using them... Just be aware that in most all conventional engines in cars and street bikes the use of synthetics is just not required. The areas that synthetics are "better" is far outside the normal operating range of the oil so that area or advantage is just not used nor needed. My main reason for posting on this thread was not to run down synthetics at all...just make sure that people understand that the idea of extended drain intervals with synthetics is not really true and not something that they should be fooled into believeing. "Extended" means a lot of different things to different people. If someone reads Amsoils [censored] and thinks that they can run their FJR 25K between oil changes they are being sadly mislead. In explaining why synthetics do not necessarily provide addtional service life it is hard to not touch on their limitations and compare them to conventional oil. The data that I see indicates that, under normal use, conventional oil functions perfectly well. When I see an engine run for 300 hours at full throttle/max load on an engine dyno with conventional oil and then at teardown the bearings are not even touched and other wear surfaces are fine it is hard to understand just how much "better" synthetic oil could have run....LOL LOL I have seen LOTS and LOTS of engines run like this and somehow, miraclously, the engines always look fine with conventional oil. And we don't even add Lucas or Slick50 or ZMax or ???? LOL LOL If you are using synthetic oil, what gain or advantage do you expect...??? I understand the idea of putting the "best" into something and if you want to use synthetic I have absolutely no problem with it....just don't expect miracles and realize that the likely hood of really exploiting the advantages of the synthetic product in a street engine is pretty slim. The proper application of synthetic lube products (in things like the VI package in conventional oil) is already being used and in the bottle of every oil you buy so the chemists that really understand the advantage of synthetic products are putting it in the correct applications for you. Yea, I agree, oil in turbocharged applications is a good candidate for synthetic. I have an air cooled backup generator for our house that we need occasionally....it gets 20W50 Mobil 1 because it will run so hot on summer days when needed. Good place for synthetic and utilizes the advantages of it. In very cold weather, there is less viscosity increase with synthetic. It will improve cranking speeds. Is it needed to help the engine down to -40....no....but it will make them easier to crank over. Like I said, I am not in any way running down synthetics...just want to make sure no one thinks that there are huge advantages to them unless they are operating the engine in a regime that forces the oil to very high or very low temperatures. The main thing that I always hate is the belief that synthetics allow much longer change intervals....a belief kept alive by Amsoil and their [censored]. The current engine oils for gasoline engines (rated GF3 or GF4 in the starburst symbol) contain synthetic friction modifiers that improve fuel economy. That is in all oils sold as "gasoline engine" oils and are the things that you want to avoid in your wet-clutch bike. Some of the "fuel economy" attributes of the oils get mixed up in the addition of the friction modifiers. A synthetic will typically be a slightly lighter weight base oil due to the flatter viscosity curve as the temperature of the oil changes. Thinner oil will always be better for fuel economy (within reason....as long as it is not so thin that metal to metal contact occurs due to lower film thicknesses) which is why manufacturer's specs went from 10W30 to 5W30 and to 0W30 in some applications. I am a newbie to this site...LOL...but not a newbie. 33 years at GM and counting....the last 20 in engine development. If you want to see what I've been working on the last few years score the May issue of Hotrod Magazine and read the article on the Supercharged Northstar for the STS-V/XLR-V. Class 8 , over-the-road diesels can go for long distances without oil changes simply because they carry a LOT of oil onboard. My brother's White/Detroit Desiel had over 20 gallons on board. So....each particle of oil doesn't spend nearly the same amount of time in the engine compared to car or bike engines that only carry 4 or 5 quarts. Since the engine has 15 times as much oil on board it can go 15 times further on a drain interval all other things being equal. So if a car engine can go 12,500 miles (best case) a truck could go nearly 200,000 just due to the extra volume of oil. This is a very very simplistic analysis and assume the truck engine beats up the oil the same as a car engine..which it doesn't, it is worse..... so take it with a grain of salt but it serves to illustrate why the longer change intervals are possible with the trucks. Several other things help. Oil coolers. Due to the heavy loads and considerable time spent at heavy throttle pulling hills and such over-the-road trucks have large oil coolers that keep the oil well below 300 even in the worst climates and steepest grades. Most of the diesels like that also use bypass filtration. They use a conventional filter that filters down to say, 20 microns, that all the oil goes thru each pass. Then, there is a smaller, 2 or 3 micron filter that only a portion of the oil goes thru. The idea is that eventually all the oil will go thru the bypass filter and catch the finest particles. So, keeping the oil cool, cleaning it thoroughtly and running LOTS of oil in the sytem allow for some long drain intervals. They don't just run the oil for longer distances without making other provisions. ZDP is a compound with Zinc and Phospates in it. It is an excellent anti-wear additive. Trouble with ZDP and gasoline engines is that it takes out the catalytic converter. Any oil the engine burns passes the zinc and phophates into the exhaust and both will contaminate and poison the cat. So....the whole emission compliance of gasoline engines depends on the catalytic converter so protecting it is primary.. That is why ZDP is minimized in gasoline engine oils and the drive is to push the concentrations even lower. That is why modern gas engines have features that I mentioned (like roller followers, roller rocker arms, no spur gears, no distributor gears, etc..) that do not require much anti-wear protection (the hydro-dynamic bearing film formed by the oil is adequate for those devices) and thus do not deplete the anti-wear additives in the oil. Want ZDP...???....go to a GM parts counter and buy a can of GM Engine Oil Supplement (EOS). It is straight 40 weight oil highly fortified with ZDP. EOS has about 10 times the ZDP of normal engine oil so it is an excellent additive to "spike" the oil with ZDP for breakin or to avoid further wear in a marginal lube situation. ZDP is expensive and has to be blended into the oil with heat so it isn't something that can just be eyedroppered into the oil. But you can use an oil that is high in ZDP (like EOS) to spike the oil in the crankcase. BTW...you don't get any ZDP in any of the aftermarket snakeoil additives. Too much ZDP can also play havoc with wet clutches so there is a balance as to how much you want in the oil. Diesels have alsways been very hard on oil due to the high pressures and temperatures in the ring belt area (due to the high compression and high pressures when combustion commences) and the fact that most all diesels are turbocharged and the turbos have oil cooled/lubed bearings. The high heat of the turbo really cooks the oil and the high ring belt temperatures and pressures will coke a lot of lube products severely. Multi-vis oils, when they first came along, had rather poor quality polymers for the VI package. Those VI packages would cook in the diesels ring belt area and stick the rings. Especially bad were the multivis oils of the mid 70's and early 80's that were SE and SF rated. In that time frame there were NO multivis diesel oils...everything that was approved for serious diesel use by Cat, Cummins, JD, etc. were all straight weight oils because of the poor quality of the available VI polymers. Interesting aside....more Oldsmobile diesels were killed by SE and SF grade 10W40 motor oil than anything else. Period. Those 10W40 oils were the "hot setup" and the "most expensive" so people bought them and put them in the Olds diesel even though the multivis oils were specifically NOT recommended .... ESPECIALLY 10W40 that has a great deal of VI in it to make the wide transition from 10 to 40. I stuck the rings in my XS1100 using 10W40 oil for the same reason because I didn't know any better back in 1980...LOL Started to use oil bad...pulled the jug off.... the rings were stuck in the grooves and wouldn't even pop out when the piston was sitting there in the open. SE/SF 10W40 was the pits and lead to the higher temperature requirements spec'd for SJ/SL/SM rated oils. Why the long story...???....Look at Rotella/Delo/Delvac oils. They are multi-vis (15W40 most commonly) AND they meet every diesel spec for NA diesels, Supercharged and Turbocharged diesels. They are excellent oils. They have to be to meet the SL and all the diesel specs and be multi-vis at the same time. Note that they do NOT meet the SG3/ SG4 requirements since they do not have the friction modifiers in them for fuel economy.
 
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the language does not match up tot he so called qualifications they spruik. an engineer doing a write up to try convince people to do something... doesn not use "$$$" and "LOL" internet garbage IMHO
 
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First off, thats not an engineer's article. They have a better way of summarizing things then this bunch of information all jumbled together. Jeesus,gives a guy a headache
 
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maybe explains GM's problems, employing an engineer who can't write concisely? (that's a joke not intended as a serious comment) I have read that fuel gauges on Holden / GM commodores down here just can't be made to work... that's a pretty basic feat of engineering to get wrong.
 
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Aren't engineers the ones who drive trains?.... I thought that post was going to end four or five times and then it kept going with subjects that were talked about before. It felt like it was just going in circles. Also why is he talking about companies who have oils for extended drain intervals for cars on a motorcycle forum? I have never seen a bottle of motorcycle oil say it was good for 15000 miles.
 
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Reminds me of the young man in my organic chemistry class. I corrected his writing on an essay question he turned in. No good sentence structure was used and the punctuation was atrocious. His explanation? "I don't need to know how to write. I'm going to be a doctor!"
 
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I'm sure if someone took a whole bunch of seperate posts all from one person (any of us on this forum) and put them all together in one long document it wouldn't sound real coherent. Many people write fast and with less care on an internet forum than they would if writing an engineering paper or an english paper, give the guy a break. I guess we have no proof that he's a GM engineer but does it really matter? A lot of what he said made a lot of sense to me. Lets just debate the content of what he said and not worry about who he was. Is what he said true or not?
 

PT1

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Synthetic oil addresses the oxidation as it will handle higher temperatures but that is about the only advantage of synthetic...so...in short, using synthetic does NOTHING to allow a longer drain interval. I am laughing....so if the oil doesn't oxidize as fast doesn't it last longer?? DOH!!! and yes I am an engineer too!!! Somebody needs to tell this guy that too much heat destroys everything...sheesh... But thanks for the laugh... BTW, trust me on this one...this kind of jibberish runs rampant in Warren....
 
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Kestas

Staff member
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ZDP?... This guy is no more an oil engineer than I am (or many others on this board). His knowledge sounds second hand, and he doesn't appear to be a senior engineer who was intimately involved in oil testing. He probably is a GM engineer, but that shouldn't make his opinion weigh any higher than some of the senior members on this board.
 
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Interesting read. He did at least cover Some of the reasons why Syn is better. Could pumpability and handling of high heat. He didn't cover TBN on Long OCI oils. He also didn't mention the tendency of Syn oils to keep an engine cleaner.
 
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 Originally Posted By: Johnny
In general there is some truth to what he said.
Just got done reading it. In general, I agree with Johnny. I think most of you are in denial. Just wait until GF5 comes out, and then [censored] only knows what the next stop for conventional oil will be after GF5. The need for syn for "most" people is becoming less and less of a reality.
 
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I did not read the whole thing but he is wrong about the ZDP in M1 EP. It's now at API SM levels. They supplemented the higher levels of ZDP with other additives.
 

dnewton3

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I, too, agree in concept, but for only part of the precepts the link put forth. Synthetics are very usefull, but only in certain circumstances. They certainly do endure temp extremes better than dino's, but they have to be EXTREME; much more than people would typically agree upon. Below -25 deg F, or well above 300 deg F. Inside those parameters, dinos do just fine. Further, I believe the synthetics can endure longer OCI's, but not extensively longer. Bypass filtration certainly helps, but that is a tool that can assist both dino and synthetics. Specific engine family characteristics certainly play into the extended OCI considerations as well. Engines known to sludge may not lend themselves to long OCIs as greatly as others. Size of the sump greatly effects the health of the oil relative to mileage; this is true. Synthetics, because of their up-market image and prices, often get more additives, thereby they tend to perform better at times. I've posted here before the question that if some dino's were as heavily loaded with additives, would the "synthetic advantage" be as great? Possibly not. The choice of lubricant used should be made as a conscious decision after a whole slew of criteria are considered. Length of OCI as a necessity, price point willing to be paid, availability, environmental expectations, etc. Synthetics are great for some uses, but not all uses. The performance gap between synthetics and dinos is closing because the advancements in dino oils outpaces the advancements in synthetic oils. For me, the use of synthetics has to meet one of two main criteria: 1) does the use of the lubricant exist in such an extreme environment that the added cost of synthetics repay with a guarantee of success, where a dino is assured to fail? 2) does the return on extended OCI equate to a similar extension of my price paid (i.e.: value - if I pay 2x the money, does the UOA support using the synthetic 2x as long?). If they answer to both is yes, then it's a no brainer to use synthetics. If the answer to both is no, then it's a no brainer to not use the synthetics. If the answer is mixed, then you have to weight the questions to what best fits your individual application; it becomes a "maybe/maybe not". It's my feeling that a lot of the time, most people don't operate in such extremes, nor get X times the OCI extension. Yet, many people that run synthetics will claim such huge benefits, often with little or no proof. In regard to this guy claiming to be a GM "engineer" - I have to say, live and let live. I am also an engineer; statistical quality control is my paid profession. I do NOT proof read most of my posts here; I don't get paid to be a BITOGer, so it doesn't get my greatest attention at times. Further, if you've read some of my own posts, you'd realize that engineers can succumb to diareha of the keyboard, and ramble on. (I'm certainly guilty of that at times). As best I can tell, he was posting on a motorcycle website; so do I, and those posts don't get any more attention than what I put into these here. It's unfair to equate how I "play" on the web with how I "work" at the job. This is just one post of a guy I've never conversed wtih. This post may have been his best work ever, or perhaps he was in a hurry to answer a question before heading out for vacation. We don't know much of the origin or the poster, in this link. While I don't accept everything I read as gospel, I don't condem either, just because some words are mis-spelled or the grammer is poor upon occasion. I try to read into the context and content, and then make decisions. In that regard, speaking of the OPs link to the GM engineer's statments, I think the concepts and general statements, if not taken with literal English in mind, fair well and are basically sound. I don't agree with everything, but I certainly do agree with some of it. If there were a newbie here, and I could impart only one thing on his/her brain before they became hardened by the BITOG experience, I'd have to say this: UOAs are the best indicator we have readily available to track lubricant health. UOAs are a DIRECT view into the viability of lubricants, because they not only tell us how the oil is doing, but how it's interacting with other mechanical systems (fuel, coolant, filtration, etc). UOAs are only an INdirect indication of equipment health. You can only make inferences as to engine health, because not all problems will show up in a UOA; particles greater than 5um cannot be generally seen in spectral analysis. With this in mind, you can make reasonable, but not guaranteed, predictions upon the continued usefulness of a lubricant with UOA analysis. Whether a lubricant is group II, II+, III, IV or V, or some home-brew inbetween, a UOA will let you know how well the fluid can continue in service. Then, you have to judge how the lubricant is faring compared to the individual criteria that are most important to the scenario, as typically defined by the owner/operator. THAT is the reality of lubricant selection.
 
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