What Is the Optimum Engine Oil Temperature?

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For a dual-purpose car, engine oil needs to be at least 220 degrees F to burn off all the deposits and accumulated water vapor. For every pound of fuel burned in an engine, the combustion process also generates a pound of water! If engine sump temperatures rarely exceed 212 degrees (water's boiling point), the water will mix with sulfur (another combustion byproduct) and create acids that can eventually damage bearings. As for ultimate power potential, the general consensus among most racers is that hot oil and cool water make more power in most engines. Cold engine oil causes excessive frictional drag on the bearings and cylinder walls. A quality conventional motor oil will tolerate oil sump temperatures up to 250 degrees, but starts breaking down over 275 degrees. The traditional approach is to try to hold oil temperatures between 230 and 260 degrees. Even on a short-duration, drag-only combo where oil is frequently changed, you would not want to routinely see oil temps under 200 degrees.

A full-synthetic oil will withstand sump temperatures in excess of 300 degrees, and for hardcore professional racing, some oval-track race teams are experimenting with ultra-thin, specially formulated, race-only synthetics operating at 350 degrees or even higher.

Also remember that a high-end engine is built as a total combination. Piston-to-wall clearances, piston ring end-gaps, and bearing clearances are specifically tailored to match the engine oil's characteristics and intended operating temperature.

This story was originally published August 29, 2013.

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