I?ve been researching oil cooling for my setup and came across the following post by DanH (logical and informative, as always):
I understand and agree with that post. And wouldn?t worry about water contents if oil operating temprature stays at around 180f degrees. What makes me wonder is why the modern car engines operate with the normal oil operating temprature at around 235-245f degrees with oil temprature redlines of 300f+ degrees while Lycoming specifies the optimal temprature of 180f degrees with the redline of 235/245f degrees? Especially while the oil viscosity specs for car engines are significantly less than those spec-ed for the aircraft engines.... if the SAE -20, -30 oils can run all day long at 235/245f degrees for hundreds of hours in car engines, SAE -50 oil certainly can handle tempratures well in access of the 235/245f redline specified by aircraft engine manufactures. Why such a big difference in oil operating tempratures between moder car engines and the aircooled aircraft engines? And should we really be concerned about our oil tempratures climbing to the 235/45f degree redline once in a while?
Granted, it is prudent to follow the engine manufacture?s guidlines, but perhaps these guidlines are a bit outdated taking into account the advances in motor oil developments, etc. There must be good reasons why the car engines are designed to run at operating oil tempratures significantly hotter than those we consider normal for aircraft engines...
Barely gets to 190? Ain't picking on 'ya, but I detect some wives tails in the air.
Lycoming recommends 180F. The standard vernatherm, if it meets specification, starts closing at 150F, and is fully seated and directing all oil flow to the cooler between 183F and 187F. The oil barely reaches 190 because the system is working perfectly.
180 is better, but there is nothing terribly wrong with 160F oil. If you're thinking "But what about boiling out the water?", consider that in the context of water removal in an aircraft engine, 212F has no relevance at all.
Water evaporates just fine at sea level standard temperature. It merely evaporates faster at higher temperatures. By 160F vapor pressure is already 18x the sea level standard. It's 29x at 180.
We don't care about boiling. Boiling point is merely the temperature at which vapor pressure exceeds local pressure at the point of bubble formation in a liquid. That temperature point drops with reduced atmospheric pressure (same vapor pressure, less local pressure). Water boils in the low 190's at 10,000 feet, not that it matters. It's just telling us we can run a lower oil temperature for the same rate of evaporation. Personally I run a case evacuator, pull 2" Hg, and at 10K my oil thinks it is at 13K, which increases water removal without decreasing oil viscosity. BTW, boiling point would be about 188F, again not that it matters.
The shutter design seen here blocks a good bit of flow when open, so I'd expect higher oil temperature in hot weather if installed. And it's pretty much for low performance parallel valve engines with no squirters, if needed at all. Angle valve motors and parallels modified for piston squirters shed a higher percentage of their waste heat via the oiling system.
I understand and agree with that post. And wouldn?t worry about water contents if oil operating temprature stays at around 180f degrees. What makes me wonder is why the modern car engines operate with the normal oil operating temprature at around 235-245f degrees with oil temprature redlines of 300f+ degrees while Lycoming specifies the optimal temprature of 180f degrees with the redline of 235/245f degrees? Especially while the oil viscosity specs for car engines are significantly less than those spec-ed for the aircraft engines.... if the SAE -20, -30 oils can run all day long at 235/245f degrees for hundreds of hours in car engines, SAE -50 oil certainly can handle tempratures well in access of the 235/245f redline specified by aircraft engine manufactures. Why such a big difference in oil operating tempratures between moder car engines and the aircooled aircraft engines? And should we really be concerned about our oil tempratures climbing to the 235/45f degree redline once in a while?
Granted, it is prudent to follow the engine manufacture?s guidlines, but perhaps these guidlines are a bit outdated taking into account the advances in motor oil developments, etc. There must be good reasons why the car engines are designed to run at operating oil tempratures significantly hotter than those we consider normal for aircraft engines...