What causes condesnsation on the dipstick?

Dear Car Talk

Dear Car Talk | Mar 01, 1990

Dear Tom and Ray:

I have a 1985 Mercury Marquis with a V-8 engine. When I pull out the dipstick to check the oil level, I sometimes see beads of moisture on the stick. What causes this?

RAY: This is caused by condensation inside the crankcase--that's the bottom end of the engine where the oil is. One of the products of combustion is water, and a little bit of water always manages to sneak into the crankcase.

TOM: Normally, when the engine stays at operating temperature for a long time, that moisture escapes through the crankcase ventilation system. But after a short trip, in which the engine never fully heats up, the moisture gets trapped inside and condenses. If you see a little bit on the dipstick or on the inside of the oil fill cap, it's nothing to worry about.

RAY: This condition is worsened, however, by frequent short trips. My guess is that's the kind of driving you do, Bill. If the engine never gets hot enough to ventilate the moisture, the condensation builds up over time, and that's not good. Cutting down on those short trips will help reduce the condensation.

TOM: So next time you need a quart of milk, try walking to the corner store instead of driving. Since you drive a Mercury Marquis with a V-8 engine, you're probably not the walking type. But try it, you might like it. It'll be good for your cardio-vascular system, and in this case, good for your car's engine as well.

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