Coolant questions
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Q. I have a 2004
A. Almost any type of contaminant in water will compromise the coolant's anticorrosion additives. Distilled or demineralized water is best. If you live in an area where the water supply is hard, it's definitely necessary. Ditto if you have a water softener, which adds a lot of sodium ions.
If the local water is really hard or has iron or sulfur content, I'd even do the last of the flush with demineralized water.
Q. Our 2004 Chevy Tahoe's ABS light came on. My wife went in to work, and when she came out the battery was dead. She jumped it, and now the truck makes a noise like something underneath is running.
I pulled the ABS fuse. To me it looks like a hydraulic pump. The pump is not running now. The regular brakes are working, but what is the problem and what should I do?
A. The ABS hydraulic pump is running continuously, but it's supposed to run only when the ABS is activated. The wiring is shorted or a relay is stuck closed.
You, or a mechanic, need to find out what's keeping the power on.
Q. I recently painted my own car. There are some places where the clearcoat has sagged, but I've figured out what went wrong: The air temperature, when I painted, was cooler than I expected. I used a thinner intended to dry properly at a higher temperature.
I've tried hand-sanding out the sags. The paint is so hard that the only result has been creating a pimple in the middle of a circular area where I've sanded back into the primer.
Do I have to sand the entire car back to primer and respray it? I sure hope not.
A. Modern automotive clearcoated enamels, which I have recently learned how to paint properly, are marvelous products. Unlike old-fashioned acrylic lacquers, however, they're unforgiving of improper environmental conditions and poor technique.
Very rarely should you hand-sand any part of an auto body. It's better to use a small block plane.
I picked up mine at the auto parts store, but to find one in your area you may need to go to a parts shop or paint store that supplies the bodywork trade, rather than to a mass marketer. It sounds like you've been to one already. The people who work the counter in these places are usually knowledgeable about the products they sell and their appropriate usage, but sometimes they're not forthcoming with that knowledge unless you know the right questions to ask.
Anyway, this inexpensive gadget uses a single-edge razor blade to shave down high spots. It's pretty good for taking off pimples, but you'll probably still have to block-sand the sag that leads to it. Adjust the blade in the plane so that it takes off the pimple in a couple of passes, not all at once.
Don't rush this process.
Get too aggressive with the razor, and it will pull out a flake of paint, and you'll be sanding down to bare metal to get rid of it.
Follow up with a hard-rubber sanding block, which you can also get at the parts store. I'm guessing that, if you recently painted the whole car, you've already got more than a passing familiarity with this device.
Wax on, wax off, as they say. Start with no-grit, wet-or-dry sandpaper and plenty of water. It takes a conscious effort to sand only the high spots and not the surrounding area. Move to 400-grit only after you've removed the high spots. If you're not down to primer, you then can scuff the entire panel with a Scotch-Brite pad and respray the panel with clearcoat.
Mike Allen is a senior editor for Popular Mechanics magazine. Questions should be sent via e-mail to driveit@nytimes.com.
