Never use air wrench on spark plugs

Dear Mike: My pickup came new with those expensive spark plugs that never need changing. Of course I needed to change them after the engine started to misfire, at about 120,000 miles.

Two of them turned out of the head fine and looked fine. I needed to use an air tool to remove two others, and they looked fine as well. Another came out with the air wrench — and took most of the threads in the cylinder head with it. I’m afraid to turn the others.

My mechanic refuses to attempt to remove them, and I can’t say I blame him. He wants a great deal of money to replace the cylinder head with the stripped threads.

Someone told me about a gadget to fix the threads, but I can tell from the amount of aluminum in the spark plug’s threads that it won’t hold. My mechanic says that the only fix is to pull the head.

Suggestions?

— G.T., Trenton, N.J.

A: As I predicted when those 100,000-mile plugs hit the market, they get mighty attached to the cylinder head after a number of years and countless hot-cold cycles. Note that those plugs are generally rated for somewhat less than your 120,000 mileage, but it’s too late now.

The newer plugs have a plating on the threads to prevent this sort of thing, but my experience in the field has shown that it’s not effective forever.

I’m old school and I like to look, so I pull the plugs every couple of years. I also carefully add a small amount of antiseize compound to the threads. Care is necessary to keep the conductive antiseize away from the electrode, insulator and wiring.

Never use an air wrench on spark plugs. Conventional wisdom says to remove plugs only from a cold engine, probably because mechanics like to tell customers that they’ll need a little time to do a job, but it’s really not about burning their hands. I don’t like to burn my hands either — but, if a plug is stuck good and solid, I’ll try again on a hot engine, because the heat makes the plug easier to break loose.

Now, about your stripped plug hole: Your mechanic has no good reason to repair your ham-fistedness on the cheap, and I don’t blame him either.

A good mechanic or machinist can drill or ream your spark-plug hole for a Heli-Coil or a threaded insert. It probably can be done without removing the head from the engine.

I do this job all the time, but I don’t recommend that you try it yourself on an expensive cylinder head.

Dear Mike: I took my two GM cars to have the antifreeze flushed. Since then two different dealers have told me that I have the wrong antifreeze, and that I need to have the green kind removed and the GM-specified brown stuff put back in.

The shop that did the flushing and refilling says no way — they say that GM’s brown stuff will eat the radiator and heater core.

— C.I., Minnesota

A: GM coolant is orange, not brown, and it’s supposed to be good for as long as 100,000 miles or 10 years in GM cars engineered to use it.

Leave your green coolant in for two years, then decide if you want to go back. Either will work, so long as you follow the manufacturer’s recommendations.

All cars will have issues with corrosion if either the orange or the green coolant is left in too long or if there is some problem with the cooling system.

Dear Mike: The local tire dealer has refused to put two snow tires on the front of my Mercury Sable wagon. He said that I had to have four snow tires to prevent the back end from breaking loose and going into a spin.

I think that, with good all-season rubber on the back and antilock brakes, this situation is unlikely, and he’s using scare tactics.

— G.C., Littleton, Mass.

A: I’ll vote with the dealer on this one. You’d be running the risk of massive oversteer on snow and massive understeer on dry or rainy surfaces. ABS comes into the equation only when the brakes are applied, and it isn’t designed for this time of situation.

My advice? Get four cheap steel-rims at a salvage lot, and swap them back and forth twice a year to save enough to pay for two more snow tires.