When do I get the most accurate reading on my dipstick?

Dear Car Talk

Dear Car Talk | Sep 01, 1995

Dear Tom and Ray:

When do I get the most accurate reading on a dipstick when checking my oil? I've heard two suggestions; when the car has been warmed up and the oil is hot, and when the car is cold and has been sitting overnight. Which is it?

RAY: When the car is cold, Dan. If you check the oil first thing in the morning, there's no ambiguity. There's no oil splashed up on the dipstick, there's no oil dripping down from the top end of the engine. What you get is an absolutely accurate reading of how much oil is in the oil pan.

TOM: Having said that, we must point out that Ford Motor Company recommends that you check the oil in your Ford when the engine is warm. Why? We have no idea. Maybe they've just calibrated their dipsticks to account for the quarter of a quart of oil that's still up inside the engine when it's warm? Maybe old Henry Ford decreed it in his will? Maybe it's part of a secret Iraqi plot to get George Bush to guest-host Live with Regis and Kathy Lee? Maybe there's a good reason, but we don't know what it is.

RAY: Besides, checking the oil first thing in the morning has other advantages. It eliminates "double dipping." When the engine's cold, there's no need to wipe off the dipstick. All the oil has settled, so you just pull out the dipstick.... look at it...and stick it back in.

TOM: Then you can go back in the house and go back to bed. What could be more perfect?

Get the Car Talk Newsletter