4.9L six cylinder...new spark plugs continue to loosen. What causes this, and what should I do to prevent it?

 

Use a Anti-Seize Compound like Never-Seez. Maybe some else has a better brand name for anti seize compound.All your plugs get loose? What brand of spark plugs are you using? This never happened to me, never heard of this happening.

 

Most of the plugs loosen. Never-seez was not used during the install. I've seen one other truck with a single loose plug but that was many years ago.

 

What brand of spark plugs are you using?

 

i get this problem too. when i bought my truck i noticed on inspection that i had loose plugs. tightend them backup and they have not come loose within the last couldple of thousand miles. but i have no idea why they would turn out.

 

I changed my plugs a few weeks back, and most were not real tight, and one was not even HAND TIGHT. Autolite 5125's. The threads were rusty, too. I gave the new plugs a little coat of oil to stop the rust, and snugged them down (also Autolite 5125s, came up recommended in the Advance Auto computer).

The oil on the threads may have been a bad idea. I'm going to pull and inspect the plugs soon, and hopefully an R&R will clear up any oil-carbon fouling on the threads that may or may not be hurting ignition.

Why would they turn out? My engine was running real lean for a while, and the added heat/vibration might have had something to do with it.

 

Just be very careful you don't over-tighten the plugs and strip the threads on the head.

 

Yes, of course. That would be bad.

It's a cast head, right?