Lubrication and Engine Cooling

Messages
33,974
Location
Southern NJ
Oil is responsible for I belive 40% of engine cooling. When your oil temps. are higher, does this mean the oil is taking the heat off the engine and allowing the actual motor to cool? I'm trying to figure out if it's better to have higher oil temps, therefore lower engine temps. or would lower oil temps. be better? I'm a confused dope. [Confused]
 
Messages
2,556
Location
Columbus Ohio
I would think that the oil will never get hotter than the engine itself, although it may be quite a bit cooler. Therefore, without sensors to measure actual engine component temps and oil temps simultaneously, I don't think that you are going to be able to determine any difference in engine cooling from the oil, in the real world. [ September 17, 2003, 08:01 PM: Message edited by: sbc350gearhead ]
 
Messages
47,635
Location
Duvall WA - Pacific NW USA
I would assume the relationship (after car is warmed up) is somewhat linear. Hotter engine, hotter oil....so I'm not exactly following your logic. The oil is taking the heat from the hot engine, yes, because the engine is hot and so follows the oil. I prefer large oil volume and thermostatic oil cooling.
 

buster

Thread starter
Messages
33,974
Location
Southern NJ
quote:
I would assume the relationship (after car is warmed up) is somewhat linear. Hotter engine, hotter oil....so I'm not exactly following your logic.
Ok, that makes sense. I think I was making it more confusing then it is. If the engine temps are higher, then the oil temps will go up. I guess what I am asking is if the oil cools by absorbing heat from the engine?
 
Messages
47,635
Location
Duvall WA - Pacific NW USA
quote:
I guess what I am asking is if the oil cools by absorbing heat from the engine?
Sure thermal energy from combustion and friction is transfered to the oil. This thermal energy in the oil, is best then transfered out of the system....via an oil cooler, the sump, etc to the air or coolant...(and then to the air) I guess some oils transfer heat better and have less frictional (generated) heat as well.
 
Messages
2,480
If oil is responsible for huh? 40% of engine cooling, then where is the heat exchange occuring? I don't have an "oil cooler" on my engine...and neither do 90% of the other vehicles out there. Bottom line is, oil does absorb some heat, but so does everything else in the engine compartment...does it cool your engine? No. The coolant and cooling system "cools" your engine....not the oil...it's secondary..and probably accounts for about 1-5% of acutal cooling...unless you have an oil cooler. And that's because the heat in the oil has nowhere to go....it's cooled (as is the rest of the engine) by the coolant and cooling system.
 

Leo

Messages
911
Location
Australia
I always had the impression that oil was always at least at the engines temperature, but usually about 5-15C higher than the water temp. I cant imagine the oil being cooler than engine temp on an engine that has been fully warmed up (at least 20 minutes driving time).
 
Messages
6,388
Location
Washington St.
The engine's coolant cools the cylinders and the head. The oil picks up the heat from the crankshaft bearings, and a bit from cam bearings, piston pin, etc., and some from the oil scraped down from the cylinder walls. Engines that have oil spray nozzles to cool the pistons will have that heat in the oil, also. The oil is mainly cooled by air passing the oil pan. There is probably some transfer of heat from the oil through the metal to the coolant in the heads. It is very common for oil to be hotter than coolant in hard operated engines, and for oil to be much cooler than coolant in lightly run engines in cool weather. There isn't a direct relationship between oil temperature and coolant temperature. Ken [ September 18, 2003, 11:37 AM: Message edited by: Ken2 ]
 

Patman

Staff member
Messages
21,989
Location
Oakville, Ontario
On cars I've driven (or ridden in) with oil temp gauges, I've noticed that the oil temp lags behind the coolant when you first start it up, and if you stay on the highway it'll end up at roughly the same temp, maybe a bit cooler. As soon as you get stuck in traffic, the oil temp goes hotter. If you drive very hard, the oil temp can go way hotter than coolant by a large amount. C5 Corvette owners who road race have seen oil temps of 300F!
 

Al

Messages
19,160
Location
Elizabethtown, Pa
Well for what its worth. And this has been discussed before : In an SAE article 2001-01-1073. They stated that when an engine is warmed up the oil temperature goes up .6 to .8 degrees F or C for every 1 degree F or C that coolant temperature goes up The other thing is that Coolant temperature is usually lower than oil sump temp. In a test of a 350 cu. in. engine the coolant temperature was 100C and the oil sump 142 C. That was for WOT at 4000 rpm. Thats a large difference. At lower loads and rpm's the differences were less. At at 2000 rpm and WOT the coolant temp was 80C and sump temp was98 C. Not sure what my point is but than again buster, I really didn't follow yours either [LOL!] [Cheers!] [ September 18, 2003, 01:00 PM: Message edited by: Al ]
 
Top