Tip on blow-out spark plugs: Don't overtighten either

GeorgeSanJose

Last Car Talk one of the callers had a problem where his spark plugs were popping out. Tom and Ray said the reason was that they were'ent installed tight enough in the first place.

Home handyman mechanics: Don't interpret this as a message to tighten the spark plugs as much as you can when you install them. Use a torque wrench and tighten them to specification, no looser, and no tighter. If you don't have a torque wrench, buy or borrow one. Too tight is as bad or worse than not tight enough.

I always coat the plug's threads with a very thin layer of moly grease prior to the install. Very thin layer, just enough to coat the threads and no more. You don't want grease getting dripping onto the firing tips of the plugs. I find doing this makes it easier to put them in with the correct tightness, and more importantly, to take them out at the end of their life span.

MikeInNH

I've NEVER EVER used a torque wrench to tight down spark-plugs. I have one...just don't use it for this. And NEVER EVER had a problem. I've never used grease...but have used anti-seize (especially on aluminum heads).

mleich

Some people have "calibrated fingers", some don't. Personally, I am in the same situation as Mike, but would recommend George's advice for others.

DfromSD

I know some engines are infamous for blowing out spark plugs even from the factory. My business had a HD Ford F450 truck that blew out two of them in the first couple months we had it.

the same mountainbike

I don't know why, but it seems that whenever anyone posts here that their plug blew out, it's always a Ford.

We've had long debates about the use of torque wrenches for plug. For many years I never used one, but I go back before aluminum was everyehere. Now, after having seen so many complaints about stripped threads, I believe in them and use one myself. Some here, very experienced people, don't believe in them.

I never use lubricant or antiseize on plugs. As a matter of fact I'd wonder if a coating would adversely affect the ability of the treads to ground out properly by creating a resistive junction. Sparplugs do electrically ground vis their threads. Like others, I've never had a problem.

GeorgeSanJose

The big advantage of using a little lube on the threads -- as I see it -- occurs when removing the plugs 2-3 years later. If the threads on the plug stick to the aluminum threads in the cylinder head after the've been in there in that harsh environment for several years, sometime you damage the threads in the cylinder head simply by unscrewing the spark plug. And if that happens, you can end up with a big and time consuming and possibly expensive job ahead of you. I learned this the hard way. I've been using a little lube during the plug install on my cars for years, and I've never had that problem occur since doing so.

mark9207

I also have never been one to use a torque wrench on spark plugs, and thanks to my father, neither is my younger brother. When he was 16, our father insisted on helping him change the spark plugs in his first car, and insisted he use a torque wrench to do it. He didn't want to because the car had an aluminum head and was quite old, and he was more comfortable going by feel. Our dad put a torque wrench to it anyhow and tore the threads right out of that head. I wasn't home at the time, so he had a friend of mine install a different spark plug and Heli-Coil for him.

I think the reason many of the blown out spark plugs we hear about are on Fords is because the Triton engines are notorious for it due to their rather shallow plug bungs. Not all of them have been Fords, though. Remember that Toyota (Matrix, I think) the dealership replaced the entire engine in over this?

Like Mike, I am a believer in anti-seize compound, as well as dielectric grease on the wires. Both make future disassembly go easier.

oldtimer 11

I also use anti-seize and tighten by hand using a 3/8 ratchet and holding only by the head of the ratchet, not the handle.

Many years ago I had a 71 VW Bus and every time I changed the plugs they felt like they were cross threading or stripping. Never did though. I knew guys who raced with flat 4 VW engines and the first thing they did was drill out the plug holes and put heli-coils in. Made changing plugs much easier.