A reader writes:
The last time I took my car to Jiffy Lube they said the engine was "full of sludge" and wanted to "flush" it to avoid such problems as the engine seizing up. I guess years of dirty oil could cause problems but is this really likely to be a real problem?

Automan replies:
To "flush" a dirty engine is a very dangerous thing. I do not recommend it under any circumstances. The best way to clean an engine that has so much internal buildup is SLOWLY by changing the oil more frequently. The gunk that goes to the bottom of the pan after a "flush" will clog the oil pump pickup screen and you can say goodbye to your engine.