Q: In a recent column you told a reader that he should not need to replace platinum-tipped spark plugs until the manufacturer-recommended 60,000 miles. The dissimilar metals in the aluminum heads and the spark plug materials make removal of the plugs difficult — which means potentially costly. Isn't waiting going to end up being more expensive?

A: Although they are dissimilar metals, the steel spark plug shells seldom seize with the aluminum cylinder heads. Mechanics used to apply anti-seize compound to the spark plug threads (some still do), but most plugs are treated and no longer require it. One notorious problem, however, was the Ford Navistar engine on which spark plugs extended extra far into the combustion chambers. A buildup of carbon made them nearly impossible to remove without damage. That is a case where the problem was avoided by replacing the plugs more often.

Missing part found

Q: I have a 2010 Mitsubishi Galant SE with 120,000 miles. Recently the "service engine soon" light came on. My mechanic ran a diagnostic test and came up with my needing to replace "the evap vent solenoid Mitsubishi part 8657A008." But Mitsubishi no longer makes this part. The dealer tells me there are none of the correct part available anywhere, and there is no alternative or workaround — but I should feel free to trade for a new car. I don't want a new car. There are lots of these still on the road. Am I being misled?

A: Auto dealers are required to have parts available for only seven years, but most cars last longer than that. When the original part becomes unavailable, I turn to the aftermarket parts companies. One such company, Dorman, sells the valve you need. Check with an auto-parts store. They likely won't have one in stock, but they can order it.

Debate heats up

Q: Something my husband does might be creating a repeating problem. He had a 2003 Dodge Durango that he ended up selling because the heat stopped working. He purchased a new 2010 Chevy Tahoe and sold that in 2018 because the heating and cooling stopped working. He bought a used Chevy Colorado with 30,000 miles two years ago. Now the heating is intermittent at best, and he is considering selling it. The common denominator seems to be that he keeps his defrost on all winter. Could this be the reason all three trucks have had the same issues?

A: Although the air conditioner runs whenever defrost is selected, it would be quite unusual for the heat to fail just because of that. The A/C draws moisture from the air, thus keeping the windshield clear. From your description, it sounds like the blend door, which mixes the hot air with the cold air, might be malfunctioning. But the chances of this happening three times in a row are questionable.

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 motormouth.tribune@gmail.com.