MAGLIOZZI

Dear Car Talk: I have a 2005 Chevy Trailblazer, which starts off fine from a cold start. After several miles, however, when I come to a stop sign or traffic light, the oil pressure gauge crashes to zero, I get a warning light that tells me I have to stop the engine, and my RPM drops below 1,000.

When I start driving again, everything returns to normal. Also, if I keep the RPM above 1,000, there is no problem. Other than this issue, everything on the dashboard reads normal.

I’ve had mechanics tell me that the engine needs to be replaced or rebuilt and that it is burning oil. I wonder if it’s not that serious and if it’s possible that the RPMs are just getting too low, and the car thinks it’s about to stall? I wonder if it’s simpler than the mechanics are making it out to be? — Greg

Um, no. Unfortunately, it’s not simpler than the mechanics are making it out to be, Greg. Well, it is simple, in one sense: All you have to do is fork over a lot of money, and they’ll fix it for you. I hate to be the bearer of bad news, but I’m afraid what you need is an engine replacement.

I think your mechanics (multiple, it seems) are right that your engine is worn out and can’t maintain proper oil pressure anymore. Here’s what happens: When your engine is properly pressurized, oil gets forced into the tiny spaces between important parts. That keeps them well-lubricated while they rub against each other at high speed.

The oil in those spaces escapes slowly. Which is OK, because the pressure is always forcing more oil in there. But when those parts get old and worn out, the spaces get bigger and the oil flows out too quickly. Then, the pump can’t maintain enough pressure to keep oil in there.

That’s when your oil warning light comes on and tells you to shut down the engine immediately, because at that point, nothing is getting properly lubricated and damage is occurring. That’s also when you start seeing plumes of blue smoke (burning oil) coming out of your tailpipe.

I’m sure that’s what your mechanics saw when you drove into their shops. Maybe if you go back during mosquito season, they’ll be happier to see you, since you can do a little free “fogging” for them. Because the oil pump is run by the engine, Greg, it pumps harder when the engine goes faster and pumps more slowly when the engine is idling. That’s why the oil pressure light usually makes its first appearance at stoplights, when the engine is turning slowly. But eventually, it’ll come on all the time.

I don’t think I’d advise putting a remanufactured engine in a car that’s already more than 20 years old — any more than I’d advise my great-grandfather to get a nose job. Some things are just not worth putting money into at this point. But you could price a used engine, if the rest of the Trailblazer is still in good shape.

Or you can just try to nurse it along for a while — you can experiment with a heavier-weight oil or turning up the idle speed to buy yourself a little time. But carry a dozen roses with you at all times, for a roadside funeral. And a screwdriver so you can take off the plates. Good luck, Greg.

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