How to get an accurate oil level reading

Dear Car Talk

Dear Car Talk | Mar 01, 1991

Dear Tom and Ray:

I have a 1990 Dodge Spirit with 29,000 miles. My problem is I can't get a true reading on the oil dipstick--whether the engine is hot or cold. Am I safe in waiting until the oil light comes on until worrying about adding a quart? How are those lights calibrated?

RAY: Well, Robert, the reason you can't get a good reading is probably because your dipstick is rubbing against the side of its tube. When you pull it out, I'll bet the dipstick is getting wiped clean or, more likely, smeared.

TOM: You should take it to back to your dealer and see if the tube or dipstick can be adjusted or replaced. It's important to be able to get an accurate reading that way.

RAY: You should definitely NOT wait for the oil light to come on. The oil light tells you when the oil PRESSURE is low, not when the oil LEVEL is low. So by the time your oil light comes on, your engine is going to need a whole lot more than a quart of oil.

TOM: In fact, if you want some hard numbers, Paul Murky of Murky Research Inc. has calculated the average cost of operating a car under such circumstances. With the oil light off, the cost of operating a car is about 27 cents a mile, and you can expect to go about 100,000 miles. With the oil light on, the cost is more like 426.48 dollars a mile with a mileage expectancy of three or less.

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