Can Darwin Trust the Dipstick?

Dear Car Talk

Dear Car Talk | Aug 11, 2015

Dear Car Talk:

My wife and I recently purchased a 2009 Pontiac Vibe with a 2.4-liter engine. For its first oil change, I bought a 5-quart jug of Mobile One oil. The owner's manual says the car takes 4.5 quarts of oil for an oil and filter change. So I measured out half a quart from the jug, and added 4.5 quarts to the engine. After starting the car and checking for leaks, I shut it off and checked the oil level. The dipstick read about a half-quart over full. My question: Should I re-mark the dipstick, or add less oil next time? Thanks for a great column and radio program.

-- Darwin

Add less oil next time, Darwin.

It's possible you didn't get out every bit of oil when you drained it. Maybe you didn't wait long enough. Or maybe the car was on a slight incline, and some of the oil pooled at one side of the pan.

In any case, it's nothing to worry about. An extra half a quart of oil in your crankcase is not going to do any harm to the engine.

If the crankcase were seriously overfilled -- say, more than a quart -- then the spinning crankshaft could come into contact with the liquid oil, and churn it up. Then you'd get oil foam.

The oil pump can't pump foam, so you could cook an engine that way.

What I'd suggest next time is to park the car on a flat surface and let the drain sit open for a good 10 minutes. Go have a coffee and a prosciutto cronut while it drains. And then start by putting 4 quarts of oil in the car.

Once you have 4 quarts in there, run the engine for a minute so the filter fills up. Then shut it off and let the oil drain down from the top of the engine into the oil pan. After it sits for a couple of minutes, check the dipstick. And if you still need more oil, add it. But definitely trust the dipstick, Darwin. Dipsticks don't lie.


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