What kind of damage is done after letting a car idle for 11 hours?

Dear Car Talk

Dear Car Talk | Aug 01, 1992

Dear Tom and Ray:

Recently, a friend of mine, who carpools to work, locked his keys in his car (a 1988 Olds Cutlass Supreme) at the meeting point for the carpool. He went on to work without realizing this. Fortunately, when he returned to his car eleven hours later, he had a spare key in his wallet (a trick he learned from his dad). Unfortunately, he had unknowingly left the motor running! To his amazement, only about a quarter tank of gas had been consumed. However, one of our friends told him that he probably did some damage to the engine block (a four cylinder engine). Is this possible? I told my friend not to worry since the engine was not really under any strain and all fluid levels seemed OK. Did he do any damage? Also, why was so little fuel consumed in an eleven hour period?

TOM: The car's fine, Cliff. People in New York City leave their cars idling for eleven hours all the time. It's called commuting on the Long Island Expressway!

RAY: Right. There are plenty of vehicles that run all day and all night. Taxicabs are another example.

TOM: And how about the police cars that are always sitting outside the Dunkin Donuts in my neighborhood!

RAY: As long as there was sufficient coolant in the car and the engine didn't overheat, everything's fine.

TOM: And the reason it used so little gas is that it was idling at 700 rpm. When the engine is running that slowly, and it's not being asked to do anything, it doesn't use much gas. In fact, tell your friend he might even consider doing this on purpose during the winter. That way, the car will already be nice and warm when he comes home from work!

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