Question on oil temperature

[bobcowan]

Originally Posted by Blas

My understanding of the process is a follows:
The PCV valve is the path to remove condensation (which is a product of combustion) from an engine as it gets warm, A cooling system temp of 185F to 195F (85C - 91c) is requires to vaporize moisture from the oil. Accumulated fuel in the oil is vaporized at a lower temperature. Under normal conditions, oil temperature is usually 15-25 degress hotter then the coolant temperature. Oil oxidizes at temperatures above 250F causing varnish deposits. The ideal temp for oil is 195F (91C) (Note: Water boils at 212F or 100C)

Hmmmm, where to begin.

- The PCV valve is there to reduce smog. By products of combustion pass the rings (blow-by) and enter the crank case. The PCV system pulls them out of the crank case and re-introduces them to the combustion chamber to be re-burned. That reduces emissions, and also reduces power.

- Condensation is not a by product of combustion. It is caused by a rapid change in temperature, which takes the water out of solution and it precipitates out - condensing into the oil or other surfaces.

- Water vaporizes at anything above ambient temp and humidity. The higher it is, the faster it happens. If it had to be >185*, your kitchen floor would never be dry.

- Oil temp is usually higher than water temp. How much depends on a lot of facters. Oil is mostly heated by rpm's. If you're racing hard on the track, oil temps will often be 50-60* higher than coolant. If you're loping down the highway on a cold morning, oil temp is often below coolant temp.

- Oil oxidizes and forms varnish at any temp than it's designed operating temp. Cheap Circle K oil may do that at 250*. But a true synthetic will easily manage temps much higher than that. And don't forget that time is a huge facter. 300* for 5 minute is much easier on oil than 250* for 5 hours.