What is an "oil purge" service...and is it worth it?

Dear Car Talk

Dear Car Talk | Apr 01, 2002

Dear Tom and Ray:

I have 97,000 miles on my Saturn, and I've always been happy with the dealer's service. I've had all of my maintenance done on schedule, and now I find that I'm putting in about 2 quarts of oil between changes, possibly more. I went to the dealership, and the mechanic suggested an "oil purge." Can you explain what this is and whether it will help? -- Jessica

RAY: Well, how to explain this delicately, Jessica? An oil purge is basically the automotive equivalent of an enema. How's that?

TOM: Delicate, as usual. Purge machines have been used on transmissions for some time, but crankcase purges are relatively new.

RAY: I've never used an oil purge machine, but to the best of my knowledge, it sucks out all of your old oil and then injects a detergent solution (heated, in some cases) into your crankcase. That detergent solution is supposed to remove any gunk that has built up over the years from lack of oil changes. And then the detergent is drained out along with the gunk, and new oil is put in.

TOM: It's certainly more thorough and cleansing than a simple oil change.

RAY: This is similar to what old-timers used to do with kerosene. They used to run a mixture of oil and kerosene into the engine to try to break up the gums and varnishes. But they did it with the engine running. And if they were lucky, they'd shut off the engine just before the kerosene completely croaked the engine. My brother used to do this with the car parked right outside the junkyard gates. That way, if his timing was off, he could just push the car in.

TOM: This "purge" machine is obviously a lot safer. But I'm not sure it's going to help you. The most likely cause of oil burning is sticky piston rings -- particularly oil-control rings. And the purge will have no effect at all on the rings or anything else in the combustion chamber. So I'm not sure the purge will do anything in your case, Jessica -- except help the dealer recoup his investment in his purge machine.

RAY: But the larger question is, why are you doing anything? You say you add 2 quarts between oil changes. If you're following the maintenance schedule, that means you're burning 2 quarts every 7,500 miles, or a quart every 3,750 miles. And that's really not much at all.

TOM: I've had cars that burned a quart of oil every 37 miles!

RAY: What do you mean "had"??

TOM: If that's really your rate of consumption, Jessica, then I would forget all about it for now, keep an eye on the oil level and make sure you add oil when needed. By the time the oil burning gets serious (say, a quart every 500 miles), your transmission might have died, or you might have won the lottery and already traded up to a Saturn L class.

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