Why go heavier?

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Jun 1, 2002
If your engine does not burn any oil between changes why would one want to go any heavier than the recommended 5/10w-30? It seems to me that a 10w-30 protects just as well as a xw-40. Since there are less VI, is not a 10w-30 the perfect weight for almost all circumstances? Why would you want to jepordize mpg with something that does not protect that much better anyways.
In the past 20 years I have used mostly 10W-30 and some 5W-30 motor oil. I have used all of the major conventional brands. In that time I have had over 250,000 miles on a Pontiac Grand Am with a 2.5 liter engine, over 150,000 miles on a Chevy Silverado with a 5.7 liter engine and 175,000 miles on a Nissan pick-up with a 2.4 liter engine. None of these engines required rebuilding or overhaul and were running great when I sold them. I am not about to try to "out smart" the engineers and put my new car warranties at risk by using an oil that is specically not approved for use.
I am one of those "walking upstream.." kinda guys, I don't really have that many followers on these oil pages. I personally think that the 10w/30 oil is marginally ok in most circumstances, and I have never lived in cold enouph climates to consider myself in those circumstances. I use 10w/30 until warranty is up and then I start going thicker, I won't say that everyone needs 20w/50 oil, but in my circumstances, I will go with half 10w/30 and half 20w/50 in my newer vehicles after about 50k miles.
My currently oldest vehicle (89 Nissan truck with 185k miles) was using 10w/40 with added stp , (used 10w/40 since it was new and just added the stp after it had about 100k miles)...has never used oil by the way (3k oil changes..)
My 99 s10 ZR2 truck is actually getting BETTER fuel mileage since I started mixing the 10w/30 and 20w/50 oil...I don't know how to explain that (I check every tank, always have on every vehicle since they were new).
(I know that several people have a problem with mixing oil wts, but I don't and the mfgrs that I have checked with have told me that there is no conflict with additives, and that it may not be an exact average for viscosity...(ex-15w/40 in my case) but is close enough. I use normal Havoline oil and consider the Chevron/Havoline to be the current (high) standard that other oils try to compete with...but that's just my opinion. I have never used synthetics, and have never seen the need for them (Remember, I have also never lived in extreme circumstances either, hot or cold,,,I've always lived in the southeast, NW Florida years ago and central NC now.)
It's your call of course, but I for one do not hold 10w/30 oil in any particularly high regard.
I have never leased a vehicle, and typically keep vehicles until about 200k miles...I will probably keep the 89 Nissan longer though, it is my work/play truck now..
I look at it this way, Chevrolet wants me to go at least 36k with no problems, the government wants us all to get good gas mileage, I want to keep my vehicle practically forever...I put MY priority first not theirs...
good luck, and everyone having a great weekend???
I'm sort of in ZR2RANDO's court here.A 40 wt (especially in syn) is probably not necessary. However I service 7 cars (including extended family) 2 of them are driven very hard and use some oil. I think the 40 wt will provide more protection and consume less oil. Now my newest vehicle (02 Nissan Sentra-2L) is my baby. I run it very easy-to the point even with auto- it probably running too low in the rpm range. I know I could change my driving habits. I currently have an oil analysis for the 10W-30 Mobil 1 and I now hav in it the 5W-30 Shaeffer's Moly Pure Syn. I plan on using Delvac 5W-40 just to compare the numbers.

An as ZR2RANDO indicated the Fuel economy is the Goverment's Bag. But really-why should I strive for increased fuel economy so the carmakers can build more SUV's??
I'm with ZR2RANDO. My reasoning is that motorcycle manufacturers recommend 10w40 and 20w50 for normal temperature ranges. Since CAFE is not a factor in their recommendation, I figure that those viscosities are better for protection of motorcycle engines and that should also be true for auto engines.

For low revving autos that are just plugging along to the store and soccer field, 10w30 would be just fine. For high performance engines and hard driven engines, I'd look at what motorcycles use for an idea on what viscosity is best.
I drive the snot out of my Firebird and use 10w30. I just made 7 or 8 quarter mile runs at the dragstrip today for instance, and will go again in a few weeks and probably make 7 or 8 more then too. And tons of WOT on the street too. I'm fully confident my oil analysis results are going to show low wear numbers with 10w30. I feel no need to go higher than this, I'll just lose MPG (it's my daily driver) and horsepower too with a thicker oil.
Rando-- Get ready for my Mark Salem quote

I'm posting this link only because it drove 'Rando nuts on Edmunds (that is I think it was you-- or some other heavy oil afficianado, I'm not digging thru. hundreds of posts to find out).

Obviously his approach is pretty simplistic for this crowd. He is, IMHO, the best of the radio mechanics and I think he's right on this one:

Al-- I just clicked on your link and the page came right up. Since I've credited him and presented the link, I'm comfortable in copying here---

"What kind of oil should I use?


My recommendation is to use a 5W-30 or 10W-30 API rated SJ-CF oil if your car doesn't use any oil between oil changes. If it has a lot of miles on it (100,000+) or it has started to use oil, use a straight 30 weight SJ-CF oil.

Let me first attempt to explain the alphabet soup that is commonly used to describe different oils. As an example, let's determine what kind of oil a 5W-30 SJ-CF oil is.

The API rating of an oil is actually a translation of the technical jargon of the American Society of Testing and Materials (ASTM) and the Society of Automotive Engineers (SAE). The SAE rating reflects how the oil will flow at particular temperature. A 5W-30 protects like a 5 weight oil when cold and protects like a 30 weight oil when hot. A straight 30 weight oil is not supposed to change viscosity so it will protect and flow like a 30 weight cold or hot. With the test results from the ASTM and the SAE rating, the API then rates the oil.

If the API rating (SJ-CF) starts with an "S" that means the oil is rated for a gasoline engine. SA, SB, SC, SD ratings are obsolete. The only current ratings are SG, SH and SJ with SG being the lowest rating and SJ being the highest. The API rating may have a dash then a CA, CB, CC, CD or a CF rating which gives the oil a diesel engine rating. Again, CA is the lowest rating, CF is the highest.

We expect that the next API change will move the gasoline rating SJ one step higher to an SK. The test the oil must pass will change and become tougher so the rating will go up one letter to reflect that. The highest rating today for a diesel oil, a "CF", is expected to stay the same for awhile.

By the way, the "W" in the SAE rating (5W-30) doesn't mean weight like most people think. It means winter.

If you drive your car hard and you are in the city 95% of your time, then you can use either a 5-30 or 10-30 SH or SJ oil. We should use an oil that protects us between the temperature range we live in. Using a 5W-30 or 10W-30 oil will generally give you 1-3% better gas mileage than a 30 weight or 20-50 weight oil. Thinner is better, both for your engine and your pocketbook.

I know that putting a thinner oil in your car goes against everything you have been taught. Most of us cringe at the thought of putting a 5W-30 in our engine. First, you must understand what motor oil is supposed to do.

1. Oil is used to provide lubrication between two moving parts to reduce wear. Most internal engine tolerances are measured in thousands of an inch and many tolerances are no thicker than a human hair. So, if you wanted to fill an opening with oil that was no thicker than a human hair, which would do a better job, peanut butter or sewing machine oil?

2. Oil is used to gather or absorb heat from the internal engine parts and carry it away. Let's say two pieces of metal are rubbing against one another at say...50 times a second or 60 MPH. If we want to flush this joint with oil and keep a continuous stream of oil running through and over it to gather the heat generated and carry it away, would you use peanut butter or sewing machine oil?

3. Oil is also used to flush the metal particles from the bearings of your engine. This one should be easy...peanut butter or sewing machine oil?

4. 90-95% of all mechanical engine wear occurs in the first 10 seconds of a cold engine start up. That initial cold start wear can equal hundreds of miles of warm engine wear.

So.... you it's your choice, peanut butter or sewing machine oil?

There are situations that call for a thicker oil. In the event your car consumes an abnormal amount of oil between oil changes, using a thicker oil would be beneficial to you. A thicker oil would, in this case, help you control the oil consumption. An abnormal amount is generally described as more than 1 quart every 1000 miles or so.

But keep in mind that every car made in 1993 and newer recommends a 5W-30 or a 10W-30. We must work to overcome the idea that thicker is better unless of course there is a reason.

I hope by now you are convinced that peanut butter type oils no longer belong inside your engine. We now know thinner is better.

My personal recommendation for the brand of oil to use is Valvoline. I have found over the years that my engines last longer and are cleaner inside than many of my customer's cars we take apart. This could also be attributed to my good maintenance habits. "
You are right, it probably was me that you drove "nuts" with that commentary by those 'salem boys'.
I disagree with them totally on the peanut butter analogy. I understand the theoretical reasons why the thinner oil saves fuel and provides sufficient lubrication, but in my experience, it never worked out that way in real life.
Every vehicle that I ever started out with 10w/30 and later started using heavier oil did not drop gas mileage enouph to notice, and I have checked every tank on every vehicle since about 1976 (back then I normally started out with 10w/40)
I am sticking with the "10w/30 is marginal" thing,
It will probably take most vehicles as long as most people keep them, but for people who really keep the vehicle for long term, like me,heavier oil is the way to go.
Manufacturers know that most vehicles are leased, or owned by a single owner for just a few years, and then they go to the next owner. If the vehicle is burning oil they always blame the previous owner for neglect. I typically buy new and keep practically forever so anything happens it is my fault (or just father time), I can't blame anybody else with neglect. Manufacturers know that most people never see most long term results of anything they do, but I routinely have.
Far as I'm concerned those 'salemboys' are "nuts".
see y'all
It is amazing. After reading this board and related boards for a long time one sees a multitude of different reports on oil brands, change intervals, all types of oil mixing, additives etc. And, most report huge success with their practice and products. It sure seems to be pointing to the direction that for 99.9 percent of the population what oil we use, when changed regularly, and/or when mixed with whatever else we throw into the mixture, does not make a hill of beans diffferece in the length of time we keep a car. All reports have had great success with their methods and whatever floats your boat seems to work. I wish their was more science to it. Lots of science in the oil formulation but the analysis of usage lags way behind
That is an interesting point SPECTOR,
I think that most of us on these posts are more involved in our vehicles than the average person is. We have probably figured out what works best in our particular situations, and after several years of experience we tend to keep on doing it.
What works well for me may not work well for someone else. I think many of us would love to be a long term tester for a manufacturer, try to see how we could make a vehicle have no oil related problems for 300k miles under several standardized type conditions. I just don't believe any manufacturer truly wants the vehicle to last as long as (at least me for sure) we would like. Any manufacturer needs the product to have a life long enouph to make a customer feel that money was well spent and then come back for more, but they also know that many customers these days don't keep any vehicle for a long time (notice how dealers really push leases, and lots of folks rarely keep a vehicle for more than 5 years (includes wrecks and family growth/lifestyle changes etc).
see y'all
Thicker oils give a safety margin when the oil gets hot.

Use a Xw30 and allow your oil temperature to go to 210F is like using Xw20 with the oil at 190F or a 10 weight oil at 170F.

I don't recall anyone saying 10w30 gives better protection than 10w40 or 15w50.
OK, I'll say it. 10W-30 gives your engine better protection than 10W-40, 'cuz non-synthetic 10w-40 will shear down to lower viscosity and offer less protection.

As for a 50wt vs. 30 wt, the viscosity your engine uses depends on many things including the bearing clearances. If the engine is built with clearances designed for 30 wt oil, and if they clearances are still tight, 30 wt oil give the correct lubrication. 50 wt might not flow correctly in those tight clearances.

Racing engines are different. They're often built with greater clearances, run as hard (& hot) as the driver can manage, and need higher viscosity for this reason.

I don't know anything about the author of that quote, except that he knows about half of what he's talking about. 5wt oil and 5W wt oil are NOT the same. Straight 30 wt, when cold, won't lube a worn engine as well as cold 10W-30, and they're the same viscosity at operating temperature, so why call for straight 30 wt after the engine has some wear? If a different oil is needed due to increased clearances, 15w-40 or syn 5W-40 would do better than 10w-40, or straight 30, or 20W-50.

I couldn't edit my post above, so I'll add hear one more item about engine design and oil viscosity...

Modern large diesel engines are putting out about 7500 hp per cylinder, and they use 30 wt. in the crankcase. Why? Because that's what the clearances are designed for. It's straight 30, 'cuz the oil is kept warm when the engine is not running. They have separate lubrication of the cylinder walls, and that'll be 50 or 60 wt (and 70 TBN due to the ~2.5% sulfur in the fuel).

Well, if the 40 wt shears down to a 30 wt than its not a 40 anymore
. If you look at your basic bearing equation where viscosity x rpm/ Load- a higher number is better and a low value. This low value can lead to bearing damage due to boundary (barrier) conditions. I think its unlikely that a 40 wt could caue any problems because at lower temperatures where the viscosity of a 30 could actually be higher than a 40 wt at higher temps (above 200F) the 30 apears to work just fine. I think the 40 wt gives you a little extra protection in boundary (barrier) conditions. It also would give an extra measure of protection at higher temps. Sorry - but I believe the 40 wt isn't recommended because of the CAFE (more Suv's needed )
And even though racing engines may have larger clearances in some areas they operate at in some cases 14000 rpm - And higher speeds usually call for a lighter oil yet they use 50 wt. Apparantly that isn't a problem.

Also folks routinely run 50 wt oils in sportbikes which run at 14K+ rpm. That also isn't a problem. (40 wt is recommended)

30 wt oils came in with the advent of the CAFE. What a surprise. So as someone above said: they have never heard any case where someone claimed that 30 wt. provided better lube than 40 wt. I still haven't also.
I forgot to add something the other day. One of the questions I asked the Havoline tech line was about the viscosity index improvers. They agreed the VII breakdown was a problem with large spread oils, the newer technologies available had also improved those VII's to where they do not break down as fast as they used to, not saying they last forever, but longer than they used to.
Maybe thats why the 0w/40 people are talking about is working ok? I've never seen it, but I've heard about it on here.
0W-40 oil is all synthetic, not petro, to my knowledge. The synthetic has a far better viscosity index and doesn't need as high a content of VII. Ditto the 5W-40 and 15W-50...synthetics.

It still has a fair amount of VII. It's just that it would be nearly impossible to make with petro oil, it would degrade so fast. Check out the analyis section, the 0w40 still loses viscosity. It went down a full grade.

I'd prefer to fully exploit the advantages of synthetic to get more protection not more fuel economy. It is a fact that the reason such grades are chosen is because they offer a compromise between economy and protection. I'm not one to compromise in that area.
I would choose a 10w40 or 15w40 in synth so there is minute to no VII and thus a greater hydrodynamic film. 10w30, 15w50(some brands)or 20w50 would also be viable depending on viscosity requirement.
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