Could transmission fluid be leaking into the crankcase?

Dear Car Talk

Dear Car Talk | Mar 01, 1993

Dear Tom and Ray:

I need help with a car problem. It's a 1976 Chevy Impala with a 350 V-8. The automatic transmission has been leaking a quart of fluid a week for about six months. The problem is that the engine oil keeps going up! A few months ago I drained out four quarts of oil from the engine to get it down to the full mark. Right now it's at a garage where five extra quarts were drained out. Can the transmission fluid get into the engine? Everyone I talk to says no, including three reputable transmission mechanics. The extra oil drained out of the engine looks and smells normal. We tested it for gas with a flame, but it didn't burn. This car belongs to my S.O. (significant other). I've accused her of adding extra oil to drive me crazy, but she says I'm already crazy enough. What do you think is going on?

TOM: Gee, Richard, I don't know. I can't think of any way transmission fluid could be getting into the crankcase. I mean, it's as unlikely as air from your front tires sneaking into the spare in your trunk.

RAY: It is possible to lose transmission fluid without seeing it on the ground. If the transmission's vacuum modulator were faulty, it could be sucking out transmission fluid and dumping it into the carburetor. If that were happening, the fluid would be combusted along with the fuel, and would come out the tailpipe as smoke.

TOM: But the increase in oil? I can think of a couple of explanations for small variations in oil plugged drain holes in the upper end of the engine, or gasoline seeping down past the rings. But neither of those would explain an extra four or five quarts.

RAY: So my theory is that someone is making a mistake. I think S.O.'s gas station attendant (a seventeen year old kid named Butch) is "checking the oil" every time she stops to get gas. But instead of pulling out the engine oil dipstick, he's accidentally checking the transmission dip stick. So every time he sees you're down a quart of TRANSMISSION fluid, he dutifully adds a quart of ENGINE OIL to the CRANKCASE.

RAY: Tell S.O. not to let anybody open the hood under any circumstances for the next month, and I'll bet this problem goes away.

TOM: And if not, why not make the most of it, Richard? Call OPEC and find out how much they'll give you per barrel.

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