Auto Tech

Oops, too much oil in your engine. Now what?

Before you figure out what to do about an overfilled engine, understand why it matters.

CNET

We all know that having too little oil in your engine is asking for big trouble. But having too much is also a potential disaster. It may be less common, but it can cause similarly catastrophic damage.

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With too much oil in your engine, its fluid level in the oil pan will be so high that it can be splashed by some of the moving parts in the engine block, specifically the crankshaft lobes and connecting rod "big ends." That, in turn, can whip the oil into a frothy consistency, like a well-emulsified salad dressing, that impedes its flow through your engine to lubricate moving parts. The result is a form of oil starvation and drastic engine wear.

"Too much oil," however, is not a precise measurement. Notice how your engine's dipstick has a range for a proper level, not a single line. Anywhere in that range is perfectly fine, as is maybe a modest amount above the top level, but I would certainly get nervous going much above that. Every engine design has different dimensions, so knowing at what level your engine oil will become French dressing is almost impossible.

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If only it were simple. Most engine dipsticks have a range of acceptable oil level, spanning about a quart, or 20 percent in most cars.

Brian Cooley/CNET

If you have significantly more oil than the top of the dipstick range, play it safe and let some out. There's nothing high-tech about the procedure: Loosen the drain plug like you do for an oil change and let out a cup or two at a time. Then snug the drain plug, start and idle your engine for a minute, shut it down, and then recheck the dipstick, wiping it once and then putting it back in for a correct reading. And do all of this while parked on a level surface, not on ramps.

If you want a fancy way to get oil out of your car, there are vacuum oil extractor pumps for under $100. These suck the oil out of your engine via a long straw that goes into the dipstick tube. Personally, I find extractors to be more work to assemble, clean and empty than the trouble they save -- and you still have to crawl under the car when your change your oil filter.