Originally Posted By: Shannow
Originally Posted By: ZeeOSix
Originally Posted By: robertcope
While I don't doubt that thicker oil may run hotter, it's running the engine at full throttle for a much higher percent of the time that gets the oil hot. It would happen regardless of the weight of the oil in there. I agree that the wording isn't great. My take is that they're just letting you know that the oil temperature light may turn on and that you can safely ignore it.
robert
Agree that much of the heating up of the oil (talking overall sump temperature) in a track situation is coming from head temperature (due to massive combustion), and the oil flowing over the heads in the valve train picking up that heat, and heat into the oil if oil squirters are impinging on the undersides of the pistons ... all that, along with heat generated due to shearing of the oil in the bearings. It's not all just due to the oil heating up in the bearings.
Never have I said that it's "ALL" from the bearings, but the majority is from viscous shear in the "bearing surfaces" including piston skirts and the like.
Never said you said that, so don't be so paranoid and think everyone is disagreeing with you (I know that's your worse nightmare
). I'm just clarifying that in an engine that's being pushed hard (ie, "massive increase in combustion" taking place), that the bulk temperature of the sump will increase significantly up and beyond what heat the bearing friction is putting in. One source of heat is from bearing RPM (as you've stated), and the other source is the heat from much increased combustion heating up the internals of the engine, and some of that heat is absorbed by the oil.
And as you know, as the sump temperature continually increases, the viscosity continually decreases, with means the delta-t caused by the oil shearing in the bearing will make the oil film area even more viscous, and that results in an ever decreasing MOFT until metal to metal contact occurs, then it's game over. That's why GM put an oil temperature warning system on the Vette. Main reason racers use large capacity sumps and oil coolers is to keep that sump bulk temperature down to give the bearing a better chance of surviving in sever racing conditions. Pulling as much heat out of the supply oil before it goes through the oiling system does a lot of good for engine durability on the track. Every NASCAR, Indy and F1 cars have crazy oil coolers for a reason.
Originally Posted By: Shannow
Most of the cylinder head surfaces, the oil is on the other side of a water cooled jacket, the oil isn't exposed to combustion temperatures except around the exhaust valve area. To get back to the sump in a typical V configuration, it spends quite some time running over yet another water heated surface in the valley, which is clearly no hotter than the coolant temperature.
My Mustang GT has a head temperature sensor, and if you run it hard for a good period the temperature will approach 250~260 deg F. In normal street driving it runs around 215~220 deg F. All the oil supply that washes over the top of the heads during valve train lubrication picks up some of that heat and takes it down into the sump to increase the sump's bulk temperature. Temperature of engine components don't stay the same temperature when you really push the engine just because it has a good cooling system. Internal components will still get hotter when the engine is continually putting out peak HP levels.
Originally Posted By: Shannow
My L67 Caprice, with a type K thermocouple down the dipstick, my normal commute at 1,700 RPM in Drive is 95C...hold it in "2" at 4,000 RPM for the same trip (i.e. same road load, more parasitic drag for sure), and I've seen 135C...Aside from the increase in parasitic loads, there's no "massive increase in combustion" taking place there.
Do that same test at WOT but holding the RPM at 4000 by towing a heavy trailer with the brakes partially on ... tell me what oil temperature you then see.
