Hi, I put together some old parts into a running engine and tried using one of the old (but didn't look old) glowplugs that had come in the box of parts. The engine ran fine with the ignitor hooked up but died abruptly when disconnected. I know there are reasons why the element will no longer maintain the catalytic reaction, but to be honest this is the first time I have encountered this personally with a seemingly good plug. Besides metal particles ruining the element what else could have caused this to happen? Some type of solvent or penetrating oil?
Thanks, Tim

Usually when that happens, your fuel is bad. Usually when the plug lights
up and fires the engine....it's good.

FBD.

I've seen the exact thing described by Tim and cured it by replacing the plug. This would indicate that the fuel was still good. Of course I've also seen it when the idle was way too rich.

Solvents like WD40 which contain silicone will render a plug worthless if used continually.

Enjoy,

Jim

W8ye, that's probably what it was, since with the new plug everything was fine. I forgot that WD has silicone in it.
Thanks for all the replies.

I disagree with Flyboy Dave. It's not the fuel that's bad, it's the plug. The element is damaged so it won't remain lit. I've seen it happen a lot, and a plug replacement always cures the problem.

For a really tough plug, try the McCoy RC 9 or 59. It's HARD to burn one of these little jewels out.

Dr.1

It probably is not burned out. When you get a coating of a foreign material (such as silicone) on the element, it shields the element from the alcohol so the alcohol can not support a catalytic reaction.

If you are the type that wants the last bit of use out of a plug, you can probably use it for bench running engines as long as you keep the booster connected in lieu of the catalytic reaction. This is handy since modern AB(X) engines throw off some metal particles at first which can partially foul a plug (taters). Save the good plugs for after this initial wear-in.

George

Often, these fouled but otherwise good plugs can be left in the flight box for a few months and sometimes will work just fine after that?

Enjoy,

Jim

I put plugs which still glow, but don't run right, into a film canister of small stuff in my field box. As Jim said above, after several months in jail they run fine again. No idea why.

different Jim

When on a tight budget, soaking the plug in acetic acid (vinigar) cleans off the inactive layer and restores catalitic action.

I'm going to try that since the plug was almost new! Thanks for the tip PE.