Oil Temperature and Engine Wear

Dr. Terry McFadden teaches a course at UAF called Arctic Engineering. It is a gold mine of tips, solid engineering, common sense and often little-known facts about coping with day-to-day problems encountered in cold climates.

If you don't like puzzles, skip the next paragraph, but I'm including it here to show the kind of problem that McFadden gives his class. It's a classic of basic engineering rationale, and requires only rudimentary mathematics and a little insight to solve. For malingerers, the answer is given at the end of this column. The problem reads:

"Some experts estimate that the wear on the rings of an internal combustion engine is as high as 0.001" per 1000 miles of operation when the oil temperature is below 170 degrees F. If the maximum allowable wear is 0.006", how long can you run your engine when the oil temperature is below 170 degrees before you wear it out?" (A 6-to-1 engine-to-wheel reduction ratio, an average running speed of 3000 rpm, and 14-inch wheels 28 inches in diameter are assumed.)

The point of this problem is to stress that by far the greatest amount of engine wear takes place before the oil is warmed up. The amount of wear that occurs afterward is insignificant by comparison.

It can be appreciated, therefore, that it is important to warm the oil, as well as the engine block. An engine that is kept warm with a circulating heater or with one that is plugged into the block can usually be started easily, but the oil is not heated and it provides very little lubrication at first. Consequently, the most engine wear occurs during the few minutes immediately after starting.

The ideal situation, of course, is to have a heater for both the engine block and the oil pan. Owners of cars with air-cooled engines like the old Volkswagen beetle know that the oil pan heaters are the only kind of heater that the engine will take (aside from dipstick heaters, and the less said about them, the better).

The answer to the problem given above is that the engine would be technically worn out after just 144 hours of cold operation. Realistically though, those 144 hours represent an awful lot of cold starts.