The Case of the Disappearing Oil

Dear Car Talk

Dear Car Talk | Sep 02, 2014

Dear Tom and Ray:

I have a 2005 Chrysler Pacifica Touring with 39,000 miles on it. The car apparently uses oil without smoking or leaking. What could it be?

-- Loretta

RAY: It could be smoking or leaking, Loretta.

TOM: There are no other choices, except larceny.

RAY: According to the principles of industrial stoichiometry, whatever goes in has to either stay in or come out. And that's true for the oil in your crankcase.

TOM: It's possible for either situation to be difficult to detect. If it's leaking very slowly, you might be leaking a few drops per mile every day between your house and the bingo parlor.

RAY: Or it could be leaking onto your hot exhaust manifold and burning up, rather than dripping onto your driveway.

TOM: Just as likely, it's sneaking past the piston rings when the engine is running, and is getting burned up and sent out the tailpipe. But in that case, it's a small-enough amount that you don't smell it, or see the telltale bluish-gray smoke.

RAY: Yet.

TOM: Right. Yet. So the first question is: How much oil are you actually losing?

RAY: If you're replacing less than a quart every 500 miles, my advice would be to forget about it.

TOM: The expense of rebuilding your engine dwarfs the cost of a quart of oil once a month. You can do the math. An engine rebuild might cost you $4,000; a quart of oil is $2.

RAY: But don't forget about it entirely. Keep a close eye on the oil level in case your rate of consumption increases -- which probably will happen eventually. You don't want to run low on the stuff.

TOM: And continue to get your oil changed at the prescribed intervals -- that will protect the engine parts that still work. Just dumping in new quarts to replace those that have leaked out or burned up does not constitute an oil change, because a lot of the sludgy oil stays in there.

RAY: I'd start keeping a log of how often you add a quart. Write down the date and mileage reading -- that's useful information. When you take your car for service, give those details to your mechanic, and ask him to take a look. If it turns out it's a leak, and it's caused by something simple like a valve cover gasket, you might as well fix it. That'd be a couple of hundred bucks, and the problem would be solved.

TOM: But if your mechanic confirms that you're burning the oil, then our advice stands: Keep an eye on the oil level and keep driving.

RAY: If you discover that you're burning more than a quart every 500 miles, then that's still our advice, but for different reasons.

TOM: It's hard to recommend putting thousands of dollars into a 10-year-old car. You could do it, but what if the transmission fails a week later?

RAY: And with the amount of driving you do -- less than 5,000 miles a year -- you could keep this car going for several years without fixing it -- as long as you keep the crankcase full and can pass your state's emissions test.

TOM: And during that time, you can be saving up for upgrade. What would you think about a nice '06 Pacifica?


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