There are statements in the archives that 190F to 230F oil sump temperature is the ideal range for most engines. Others narrow it down a bit more to 220°-230° F
Are these indeed considered optimum (or nearly so) target temps?
Zoz, Steve, et. al., Engine Lubrication Model for Sump Oil Temperature Prediction, SAE Paper 2001-01-1073, states
"The predicted sump (bulk) oil temperature versus the coolant temperature was shown to be about 18 to 20 degrees C higher* for the oil than for the coolant at 2,000 RPM WOT. At 4,000 RPM WOT, the oil sump temperature was about 50 degrees C higher than the coolant temperature. The slope for both RPM ranges was about 0.7 C/C, which means that on the average, the Oil Sump temperature is always 1.2 to 1.43 times higher than the coolant temp."
The word "predicted" stood out to me above - not sure if actual measurements were taken
It takes longer for oil to heat up than coolant, upon cold start up
An oil temperature gauge would likely be the best route - and I'll explore installation options - but wanted to just ask basic questions wrt to t-stats, etc
Does the condition of the radiator and block coolant passageways mostly & ultimately determine upper/operating oil temp (and to a lesser degree coolant/water mix/product used)?
Phrased this way - say you have an 180F t-stat and a 195F t-stat, both under identical conditions. The 195F t-stat will initially stay closed longer, letting the oil warm up faster, which is desirable
Once both t-stats are open - let's say on the highway w/o any cooling fans running - does the radiator condition mostly determine what temperature equilibrium will be obtained?
And - a wordy post to ask simple questions - will both the 180F & 195F t-stats remain fully open, so their respective temp ratings, at the upper side of engine operating temp, is moot?
I.e., partial closing and full opening, or cycling, with a fully warmed up engine, is NOT occurring...right?
So why do some/many install cooler than spec t-stats?