See more of the story

Q: I bought a used 2008 Chevy Trailblazer several years ago. I really like it. But a while ago, I noticed that when I drive for 30 or 40 minutes, the voltage on the dash would go down. It still started normally, so I didn't worry about it. Then, one day, it didn't start. The tow truck driver jumped it, and I went to get it fixed.

They said I needed a new battery and alternator, so I had them replace both. After short drives, it seemed OK. But on the next long drive, the voltage went down again. I plugged in a digital voltmeter. Right after starting, the voltage would go up to 15 volts, then gradually decrease, until it went down to 12.2 volts. I went back to the shop, and they replaced the alternator. Same story. A third alternator; same story. A different brand alternator; same story. The gauge on the dash shows the same thing, just not as precise. Is there something in this model that could cause this?

A: What you are seeing is perfectly normal. A fully charged battery will show 12.2 volts. Any drain on the battery, such as using the starter, lowers the voltage. It is the alternator's job to get the voltage back up, and it does this at a rate of 14.7 volts. That is close to your 15-volt reading. I would question the skill of a shop that replaced all those alternators without significant diagnosis.

Bad radiator or bad advice?

Q: I have a 2013 Dodge Durango V-6, purchased new, with 44,000 miles. The last couple times I took it to my mechanic for an oil change, he pointed out coolant residue on the side of the radiator. He told me that I will soon need a new radiator, at a cost of $1,000. I have seen no sign of coolant leakage on my garage floor. I checked the coolant level by removing the radiator cap one morning, before starting the engine. The cold coolant level was at the top of the radiator. When the engine is fully warm, the temp gauge reads below the halfway mark.

I don't believe I need a new radiator, but I am starting to wonder if I need a new mechanic. What do you think?

A: If the leak travels along something hot, the coolant evaporates, but like a garden slug, leaves a trail. That might be why there is no dampness on your floor. And coolant from the reserve tank could explain why the radiator was full when you checked it.

You might need a radiator eventually. But before you plunk down a grand on a new one, try some cooling system stop leak. Having used it, I can vouch for Bar's Leaks brand.

Give folks a break

Q: Just outside my hometown, there is a sign that reads, "Engine braking prohibited." What does this mean?

A: It warns truckers not to use jake brakes (engine compression release braking) or downshifts, both of which produce noise, in the area.

Bob Weber is a writer, mechanic and ASE-certified Master Automobile Technician. His writing has appeared in automotive trade publications, Consumer Guide and Consumers Digest. Send automotive questions along with name and town to