desired oil temp
desired oil temp
(OP)
Any recommendations for oil temp in a motor?
Gas engine?
Race vs street?
Diesel? (especially diesel!)
My knee jerk reaction would be to aim for slightly over 212F to boil the water out.
Sources? Books/articles?
Jason
Gas engine?
Race vs street?
Diesel? (especially diesel!)
My knee jerk reaction would be to aim for slightly over 212F to boil the water out.
Sources? Books/articles?
Jason





RE: desired oil temp
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Note that:
> there shouldn't be water anywhere in the first place
> you do not need anything close 212°F to evaporate water, 180°F will do it; it just takes longer, but your engine will also last much longer
TTFN
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RE: desired oil temp
Given all that---In our race cars, I shoot for about 220f in the sump and ~180/190f after the oil pump/filter/cooler and back into the main oil gallery. It does not always work out that way, but using good $ynthetic 40 or 50 race oil temps as high as 250 in the sump cause no problems. Of course, oil is changed after each race weekend.
In my old Dodge/Cummins with it's 13 qt. capacity and a factory heat exchanger, I have never seen oil temps above about 190f, even after a long pull at high speed when the outside temp was hovering in the 100f+ range. At somewhere between 300k and 400k miles (the odo broke at 186k about ten years ago), she still performs as she did when new. What can I say? Still gets ~20 mpg, too.
Rod
RE: desired oil temp
on some smaller diesels we set an upper alarm limit (derate) on oil from the cooler at 110C.
A good rule of thumb for max allowable cylinder wall temperature at top ring turnaround is ~180C. That'd be about as hot as the oil can get at that location without oxidizing too quickly.
@IR: there will always be water present if oil temps aren't kept high enough - about 1-2% of the combustion products travel through the crankcase (gasoline or diesel), and there is a great deal of water vapor in the combustion products.
RE: desired oil temp
TTFN
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RE: desired oil temp
Changing to a hotter thermostat (195 vs 170) has crossed my mind as well.
I'm considering using a racing engine diaper as an oil pan insulator as well.
...but if cold is fine, then it's all good.
Jason.
RE: desired oil temp
TTFN
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RE: desired oil temp
RE: desired oil temp
TTFN
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RE: desired oil temp
Regards
Pat
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RE: desired oil temp
RE: desired oil temp
RE: desired oil temp
Mike Halloran
Pembroke Pines, FL, USA
RE: desired oil temp
That is exactly what I did on my old hot rodded air cooled VW engines with added on external oil coolers. Together with a change to Mobil 1 it gave a dramatic increase in engine life from maybe 10,000 miles to over 80,000 miles.
Regards
Pat
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RE: desired oil temp
I race an '87 BMW and have collected a lot of data on oil over the years. One of the things I learned is that oil temps can vary more widely than would would expect, depending on exactly how you measure it.
As a result, one has to be cautious when they compare oil temps between cars. Just because an oil temp sensor seems to be "in the flow" doesn't mean it really is. Just because the temp sensor in the pan "ought to be submerged", doesn't mean that it always is. And finally, the local temp of an engine block will vary wildly depending on how far you are from the water jacket.
RE: desired oil temp
There's no ideal temp, but there's an ideal range. Here's some variables to consider.
Optimum viscosity at temp. An oil's "Weight" XwY describes it's cold (0degC) and hot (100degC) viscosity. X is cold and Y is hot. The curve of visc vs. temp is non-linear. Temp differences around 0deg create big differences in visc and temp differences around 100deg don't make much difference. So the visc difference of an oil at 0degC vs. 10degC is large, and the visc difference between 90degC and 100degC oil isn't very big. Therefore in terms of viscosity it doesn't matter much if your oil is 10deg this way or that.
And if visc was a problem, just go to a thicker or thinner oil.
Note that those XwY values are actually a band of viscosities and one 20W50 can vary from another 20W50 by easily 20%.
Boiling out impurities. Oil doesn't heat up in an engine nearly as fast as coolant. My commute is 22min and as a result my oil doesn't get to operating temp. Oil needs to get hot to boil out fuel and water. If it doesn't get hot the fuel and water accumulates and it doesn't take much of each to either cut the visc of the oil in half or turn it into chocolate milk.
Engine Management. Racers spend a lot of time at the dyno. In my class we are not allowed to mess with our engine managegment. Therefore we spend a lot of time trying to understand how that "black box", the car's ECU works. One of the things we learned is that the ECU seems to start dialing back power when the coolant temp approaches 210deg F. Sure, a cool intake tract equals power. But your engine management may decide that a cool engine means power. Therefore there would be advantage in keeping your oil cool.
Thin hot oil is slippery oil. Not necessarily. Oil is complicated. Oil OEMs do all sorts of interesting things with oil additives to improve oil characteristics. Some publish their data and some don't. Every race oil I know of is thin. But some relatively thick oils seem to beat relatively thin oils at the dyno and in various tests designed to measure oil efficiency. So gaining efficiency and power from oil is more complicated than simply choosing a thin oil.
RE: desired oil temp
RE: desired oil temp
I've configured my oiling system a lot of different ways. When my oil was running hot it was 220-230deg. Last year it was 185-195degF. As I began to understand that there was a power advantage in keeping the engine cool I worked harder to cool it.
There is no generic answer. Just keep your oil temp within a reasonable range. If you start getting obsessed with this stuff you'll just turn into me.
Re. oil pressure. There's no generic "right" OP. Every model engine is different, and it can be terribly difficult to find folks that really know what they are talking about. The Internet is full of folks who aggresively assert "My car loves <brandX>" as if they tear their engine down each year, do oil analysis after each event, and have a pile of SAE mags in the bathroom.
RE: desired oil temp
There's various ways to measure and test how well an oil will provide hydrodynamic lubrication and I'm no specialist. But the common measure is HTHS...High Temp Shear. All else being equal, thick oils have high HTHS. So in the case of that article linked, all the owner needed to do to restore adequate hydrodynamic lubrication in the face of high temps was to choose an oil with higher HTHS.
RE: desired oil temp
The temperature of the oil can affect its viscosity, which in turn can affect the fluid film thickness in hydrodynamic contacts such as crank bearings. If the fluid film thickness in the contact becomes less than the surface asperity heights (lambda ratio), friction and heating will increase and cause rapid deterioration of the bearing and journal surfaces.
The temperature of the oil can also affect the heat transfer rate of components that rely on oil flow for cooling. Many materials in an engine can lose fatigue life if exposed to temperatures above their design limits.
The extreme upper temperature limit for engine oils is usually determined by their flash point. Flash point can be an issue for lubrication of the upper cylinder liner surfaces. The compression ring briefly operates in boundary lubrication conditions around TDC, which also coincides with peak gas pressure loads and temperatures during the combustion cycle. Even though the outer surface of the liner is liquid cooled, if the inner surface of the liner gets hot enough to flash the oil film, then ring scuffing is likely to occur.
The only benefit to using very high oil temps that I can think of is that a smaller oil heat exchanger can be used.
RE: desired oil temp
RE: desired oil temp
RE: desired oil temp
Regards
Pat
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RE: desired oil temp
Non-mass-conserving bearing simulation schemes gave "close enough" answers to design successful engines for a decade or two... and the simple "cavitation" models are an improvement in accuracy. I'm not sure there is a practical need for a mechanistic or even table-based vaporization representation (perhaps that was what was meant by "flash point" above?)