Correlation between water temp and oil temp
 

I'm curious about the correlation between water and oil temp. Anybody with an oil temp gauge have an idea about what temperature the oil will be at compared to water temp?

not a mechanic, but heard toyota's oil sludge issues were coolant(water) related. it had something to do w/ them narrowing or widening the coolant passages, experimenting to try reduce weight possibly(if it ain't broke, don't fix it).

anyway, the increased heat, along w/ too long recommended oil change intervals caused the oil to be "cooked" and then sludge up. lots of class action law suits were and still are pending. luckily for toyota, only the v6s(i believe) on very few year models applied before the problem was corrected.

hope that helps ya!

I've had both guages in the past and have some observations:

1. Usually from a cold start, the water temp will come up first. The oil temp comes up a little time later and seems to be a better indication of a fully warmed up engine (the time at which the peformance and FE will be pretty much normalized for that engine).

2. Unless you have an oil cooler, the oil temp will generally get higher than the coolant but the oil temp will vary with the amount of power the engine is producing (I've noticed the latter in both cars and recip-engened aircraft).

3. When using petroleum lubicrants, the oil temp will reach higher levels when the oil is old and dirty (and presumably beginning to break down).

I hope this helps.

Oil Temp vs. Water Temp
 

I had an oil temperature gauge in my 1980 Rabbit.
The oil temperature crept up quite slowly and varied with outdoor temperature. Even during the summer it seemed to take 25+ minutes to reach a steady temperature.

Thanks this is the kind of info I'm looking for. Most are running grill blocks and belly pans. I see 210-215 on the water temp all the time. The high end of oil viscosity is tested at 100c or 212 degrees . So If the oil temp runs hotter then water temperature, under normal loads, would it be better not to go with a lighter viscosity oil?

I'm flirting with the limit of my knowledge here, but if I had hotspots or high oil temps, I'd probably go with synthetic. As for the oil's coolant properties, and depending on the engine's oil circulation flow rate, there must be an optimum tradeoff between high and low viscosity oil. Engines have improved greatly in this area over the years (I used factory-rec. 0W30 synth in my '97 VW and 20W50 dino in my '61 Healey).

Maybe someone with more knowledge of engine internals could weigh-in here.