Does synth's base oil make engines run cooler

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May 27, 2002
Ocala, Florida
Does synth's base oil make engines run cooler than a dino's base oil in the same engine under normal conditions?

I suspect this will turn out to be a hot topic as I for one don't believe that you'll not see much if any noticable difference in temps from changing over from a dino to a synth. Yet I hear way too many claiming it does. Well now is the time to show us non believers how it does.

In the many oil changes and different oils used, I have never seen an instance where the synth base oil has made any difference in temps, at least not no 10 to 20degs as some claim.

I ran across an engineer that made some interesting comments and totally agree with this so here is a copy of his post....

I have done a bit of testing here, with both head temp and oil temp gauges in my car for thousands and thousands and thousands of miles over every terrain I can think of under every loading condition I can imagine. All my testing was done in the late 1990's and early 2000's - not the 1970's. I've used conventional oils, hydrocracked petroleums (i.e. legally "synthetic," but not really synthetic), and true synthetics in aircooled vehicles.

Effect on head temperature? ZERO.

Effect on oil temperature? Depending on your choice of oil, you may notice no difference or a very slight drop in oil temperature.

Now, when you are pushing the limits and holding a highish rpm for a long period of time, your oil temp will skyrocket unless you have some nice coolers. I've baked conventional oils before... the smell is unmistakable :). I have been unsuccessful at baking a synthetic oil. Even when running with no oil cooler and sustaining a 275F+ oil temperature, I couldn't even get a hydrocracked petroleum oil to bake. Oil pressure didn't die either. These findings are very helpful to us heavy-footed fellows :).

Take care,

Shad Laws
LN Engineering

Now interesting thing here is unless an oil is pushed to extremes, like what he had done, you wont see any real differences. Only when you need an oil that can withstand heat for long durations will a synth or even a blend will give you the performance differences. But as for lowering the operating temp under normal conditions, I have yet to see this. I have taken temps with motors and bearings alike having changed to full synths' and have not seen this to make the difference. I'd be interested to see how well the newer SL grades would hold up in comparision now.

Where the difference is, the additive package more so than the base oil itself.
I've honestly never noticed any difference at all in engine temperature on a car when I switched it over to synthetic, whether it was on a used car I bought, or with a new car. For that matter I've never noticed a huge increase in gas mileage either, definitely no more than 0.5 MPG (which is why I doubt it when someone claims to get 3-4 MPG more, like in some of the Amsoil testimonials they publish)

[ June 14, 2002, 04:47 PM: Message edited by: Patman ]
in my last car, when i switched to mobil1 tri-synth my temperature gage did drop ever so slightly.

gas mileage did improve, on average, about .5 to 1 mpg.

the vast majority of my miles are highway.

i haven't switched the new car yet, but the next oil change will be synth. i'll post when i get some mileage reports and check my temperature gage.
I have never seen any change in engine temp when switching to synth.

I have also never noticed any change in mileage, even when going to synth in engine, tranny, and diff.

Of course, it's pretty hard to notice a .25-.5 MPG change. Of course in my car I can make a 5-10 MPG change, just by my mood, whether I'm feeling frisky or not...

Synthetics are known to free up a little power, but we are generally talking about 1-2%, so why would you see more than a 1-2% increase in mileage?

[ June 14, 2002, 05:09 PM: Message edited by: VaderSS ]

In my 1986 Sub I have noticed lower coolant temperatures (in the engine) with synth's I see 5 to 20 degrees (F) lower coolant temps. (depending on load), but in my other vehicles, I cannot tell, since their gages are not as sensitive, and in one case, actual temps are not marked!

We are talking here about three different temps I think; Head temp, coolant temps, and oil temps. The oil is the main coolant for the engine (about 60%) where the coolant provides about 40% of the cooling. That's why I am a firm believer in engine oil coolers.

The engine rejects heat by a number of methods:
1. Radiation from the block mass (IR).
2. Exhaust gasses.
3. Oil
4. Coolant.

From the theoretical standpoint, synthetic base oils have higher thermal conductivity
coefficients than do their dino counterparts, so they should transfer heat more effectively, which translates to better heat rejection, I.E, they transfer heat quicker and eliminate heat buildup. Add to that lower coefficients of friction (especially for mulitvis') for synth's and you have should have lower operating temps.

I know my Briggs and Kholer engines operate cooler with the synthetics. I placed a contact thermo on them and actually proved a lower (50 F) temp in the middle of summer. (Contact with aluminum head).

Here's another question in the same vein:
The newer coolant thermostats are more accurate than the older ones and tend to keep a more constant temperature, for emission purposes. So unless you have an older vehicle, how would you tell a temp difference unless you instrument the engine? I guess one way would be to see how fast the temp rose (with the two different bases) from the same starting (ambient) temperature.
I disagree with the statement that oil provides 60% of a water cooled engine's cooling.

1/3 of heat produced in an engine goes out the tailpipe. Another 1/3 actually makes power. The majority of the remaining 1/3 is removed by coolant system.

Oil does serve as a localized cooling medium within the engine, but that heat has to go somewhere, and the liquid cooling system has far more area in the radiator, than the engine has radiation area which is the only place that the oil has direct contact with a heat removal source.

The majority of watercooled engines do not have an oil cooler. Mine has one(the first car I've owned with one), but it is in the radiator, cooled by water. Where is the heat that the oil collects to go, if it's not the cooling system?

On vehicles where oil is one of the primary coolants, The Suzuki GSXR series comes to mind, the oil cooler is as big as the radiator would be if it were watercooled, and traditional air cooling of the cylinders still provides agood portion of the cooling on these engines.

[ June 14, 2002, 06:06 PM: Message edited by: VaderSS ]
Do not expect your coolant temperature to drop by changing over to a synthetic engine oil. Look for a reduction in oil temperature - if there was something to this theory, that's where results will be found.
I am thinking it will be shown as the thread furthers along that a thinner oil at least in theory"0/30 vs 20/50" will remove some MINOR temp from the internal parts of the motor,but that it would do this either with or without synthetic because it would drain back to the pan faster only.

I respect what that Enginner had to say but suggest he should have tried "burning" that mineral oil he was using while it was fresh

275f for substained periods are nothing to compare with how a 82 Suzuki GS 1100 would heat up an oil + "325f".That motor used 82 tech Shell Fire and Ice 10/40 and I thought the guy was utterly stupid for using that light of an oil back then. I tore into the motor for him to do some heavy modicications after about 12k of abusive torture,,no signs of coking or other oil related problems,,especially in the exhaust cam area where a high Lobe Center Angle will create some heat for a motor.The key to success is if you are going to abuse your motor,abuse it with fresher oil.Yes,he might have been doing it for test purposes but there is another side of the coin there!

Motor designs still come into play when testing oils,,apples to apples cannot quite be obtained.

Off topic of thread ,I know but ?

[ June 15, 2002, 07:41 AM: Message edited by: dragboat ]
In theory, synthetics are more slipery, therefore reduce the heat generated by friction.
As to the question of cooling, sure some of the heat goes out the pipe and other is used for power. It is the rest I think we are concerned with, much of that is carried by oil and the oil pan. Much of the heat also has to do with your driving speed, wind, etc. I once drove a nissan across Florida in the summer without a cooling fan. Just had to maintain the speed that the temp guage said was safe. a couple of miles higher or lower and it heated up. Air circulating over and under the engine, combined with the radiator takes it away.
Synthetics really aren't more slippery though, as it isn't the base oil which provides the
antiwear properties, it's the additive package.
When I quoted the heat transfer figures
I was quoting from memory, but have since
found some data from Heywood's book
on "Internal Combustion Engines."

He starts with 100% fuel power (Energy/time)
and split the figures up. Here is the SI engine

Brake - 27% (power to road)
Cooling - 25%
Oil - 14%
Exhaust 30%

Brake - 35%
Cooling - 28%
Oil - 8%
Exhaust - 27%

The other 3% is split up as follows:
2% for convection cooling (air past engine)
1% radiative cooling.

********End of Book Data**********

In the head /cylinder system, the heat of
combustion is transferred to the head via direct
conduction and in the cylinder, through conduction
by the oil film. The heat conducted to the head is carried off by the coolant fluid
(forced convection cooling) and the oil transfers
its heat to the cylinder block, where again, coolant fluid
carries most of that heat away.

In air-cooled engines the heat of combustion
is conducted to the head and to the oil, where
through forced convection the head carries the
heat to the environment.
This brings me to the point I think many miss.

Heat is cause by what? friction... As most have seen very little people see much if any difference in heat disappation due to switching over to synths as there is no place to move the heat to.

So, how does the heat get reduced? By reducing the friction.. Ok, here's where you synth die hards are going to freak on me....

I personally find that the hydrodynamic properties of both synth and mineral if comparing apples to apples, will react the same. Both hydrodynamic films of mineral and synth will shear out when two surfaces are squeezed to gether. Don't believe it? Why do we have EP additives in a grease? The hydrodynamic film properties of grease is much higher than that of any motor oil, of course there is oil in the grease yet, when the surfaces come together, the film is squeezed to the front and rear of the bearing thus relying on the barrier additive.

Same priciple applies, No, the extreme levels of shearing isn't the same in a motor but the priciples are the same. There is enough shearing of the film or squeezing out due to the scraping of the rings, or the cam squeezing out the film when riding against the valve, or in toyota's case where the ohc's gears push against each other all of these areas create a momentary shearing effect of the hydrodynamic film. This is especially true when people abuse their engines. This is why some one who doesn't push an engine will not experience the problems as someone that does.
case in point of shearing...
This is due to the piston being pushed against the crank causing the oil to squeeze out and causing the bearing scuffing on the top, unlike the bottom
where this just rides back up while the other pistons are doing the pushing.

So, by the addition of barrier additives, you can reduce friction and wear due to shearing of the hydrodynamic film. Now when this is applied, you will see a difference in temps as it doesn't allow as much friction as well as helps increase milage and hp. This is especially true in manual trannies and rearends moreso than the engines themselves.

Again, My stance is, synth's don't protect any better than mineral if both are using the same basic additive package, but synth's will protect longer(not so much nowadays due to the new SL and synth defintions) than a mineral due to the base stock handling heat for longer durations, and Synths do seem to have had an advantage over minerals due to the lower cold weather pumpability, which again, the gap closes.

I have taken a inf red temp gun and shot temps on motor bearing using a standard iso 30 lubricant, switched it to a full synth iso 30, same results, then switched it to a iso 30 with a moly ep additive, and the temps dropped.

When a person changes from a mineral to a synth, and the temp drops, can you say for a fact that it was the base oil that droped it or maybe the barrier additive possibly?

anyway, go head you synth die hards, jump all over this as I know it's a coming!

IF you define "slippery" as reducing friction, the synthetic bases (PAO's and Esters) have a lower "coefficient of friction" than do dinos, from every ASTM and SAE test that I have read.

The Lower the coefficient of friction the more slippery is the base oil and the less heat buildup on sliding surfaces.

In one paper, it stated that for every 10% reduction in overall friction you have about 3%
increase in gas mileage.

You have taken a close-minded aproach on this from the very moment that you typed this post - why ask a question that you apparently already know the answer to?

"Does synth's base oil make engines run cooler than a dino's base oil in the same engine under normal conditions?"

If you are talking about reducing oil temperature in an engine by using a synthetic, then do the real comparison test and post the results, I am sure that we would all find it informative. Taking a temp. shot on an electric motor bearing is not the same thing as collecting data from a real engine under real conditions.

[ June 16, 2002, 12:06 AM: Message edited by: GW ]
Sorry Gw,

Yes, I started this with the intent to get people to really look at all these claims of synth's reducing heat.

First everything I have done is in my personal quest to see for myself what happens if.. and as the engineer stated he saw no difference, I have stated the same as many others on here. I know you really hate this but understand there is enough technical BS and myself, I like to see and hear real experiences and not get caught up in the cubical engineering data as this looks good on papaer but not always work out the way you'd think.(thats happened to me more than once)

The experience with the motor was under real life conditions at a power plant here in jville over the course of 3 months. Does it compare with an engine? I think it actually takes a lot of other varibles out of the equation about the reduction of heat, since there is no water temp, no oil pump(slinger), no gas blowbys and such.

I found it to be interesting and can see how it can relate in an engine as well. Lubrication pricipals are generally the same, load,friction, ect.. ect... and the question was based on base synth oils vs base mineral oils cooling properties. engine or otherwise.
I agree with all you have said about the oils ect except I don't "think" that upper rod bearing was damaged by "shear" .The area the damage area looks to be from another problem,,could be oil pump cavitation or the overlay of the bearing was faulty or other crank round problems,the radius fillet of the journel ect.If the rod was not elongated and no other problems the damage would have been a perfect pattern.

If the top of the bearing shell looked like the bottom I would have just agreed,,but it is not and although shear might have been involved,that motor had something else wrong in my opinion

I like how you have done you testing I know others have questioned but this is just another example of how apples to apples cannot be applied,,even in the same engine family.Too many variables to go wrong. At least your way of testing is controlled to exactness
My heat transfer figures are also from memory and some common sense. I have to question these figures.

Brake - 27% (power to road)
Cooling - 25%
Oil - 14%
Exhaust 30%

Brake - 35%
Cooling - 28%
Oil - 8%
Exhaust - 27%

2% convection
1% radiative

1st off, I feel that each engine design is different and that different designs will put more heat into the oil, oil jet cooled pistons on some engines would put more heat into the oil. With that caveat I feel that the above figures make for good generic figures and probably do come close to my engines figures.

Normal oil temps on the Impala, which has a standard oil to water cooler, on a 100F day range around 190-200F. In road racing, they peak at about 230.

People in the Impala world have pulled their colers have found that temps went from the normal range to staying at about 210-230 on a 100F day. This is hardly stressing the oil. Of course if you are towing or road racing, you would want the cooler in place... But the average person does not road race, and most Impala owners don't tow, even though a properly equipped Impala can handle 7000 LBs.

If a car has no oil cooler though, which is more common than having one, then the heat that the oil collects has to go somewhere, and that is into the block, where it is removed by coolant, convection, and radiation. In these cases, the percentages would be more like the following;

Brake - 27% (power to road)
Cooling - 39%
Oil - 0%
Exhaust 30%
2% convection
1% radiative

As to the claims of synthetics reducing friction, that has been proven on the dyno, with a complete mobil 1 package(pre moly days), from front to rear, giving an extra 1-2% more power to the rear wheels.
Well Dragboat, before you're climbed on by others, Let me say this is the only test that I have posted where I used this level of acruaracy as it was in a plant survey and we used this to examine the effects of how barrier additives make a difference in temperature, as well as actual vibrations in that motor. To show more of this picture, we also used a power analyizer which is hooked up to the power panel controller box for the motor to establish the difference in power savings with the moly oil vs the others. This also analyized and shows the difference in the vibration analysis showing that at certain harmonic levels where it was lowered to a much lower level than when it was running the other oils. All during this time, there was no readjustments to any shims or alignments, just the lubricant was changed.

I guess, now that I'm thinking about it, I have heard many people state that they noticed their engines seemed to run smoother as well as quiter when they switched over to Schaeffers. I just never thought much about it but now reflecting, this is another proven point using these tests that actually establish what they are stating. (and all this time I just chalked it up as possible placebo effect, go figure).

As for the pictured bearing, All of the bearings that came out of this engine was near identical. This engine had an overheating problem due to a block problem. This may have contributed to this wear pattern but in further investigations with other machinists, I have learned that this is not uncommon to have the upper bearing show more wear than the bottom one until the bearings start to have so much wear that the whole rod becomes loose then both would become worn equally, this is especially in extremem higher milage motors.

I even picked up a set of plain bearings out of several other motors laying around at the machine shops and they showed the same wear patterns, top worn more than bottom. Again, establishing to me the shearing effect of oil in high shear zones.

Vanderss, I'm sorry but are you sure pre moly days? Moly has been used since the 40's in industrial and farming applications. Also, again, you're talking about two oils, what is the difference in the antiwear/ep additive levels between the two? were they the same or did the new improved synth oil have a better or higher level of friction modifiers that was not taken into account and just assumed that since it was a synth it had better wear protection?

[ June 16, 2002, 09:34 AM: Message edited by: BOBISTHEOILGUY ]

Was this engine run on synthetics, dino with Moly or dino without Moly? Just trying to get some kind of baseline here!

From the wear pattern, I would certainly like to have seen the micrometer readings on that particular crank. From what I can see, the wear paatern is indicative of eccentricity of the crank.
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