Glow plug questions

Another quick question... and BTW appreciate all the help so far... Have a .47 GMS aircraft engine. Should the glow plug be removed and cleaned after every use? If so what should I clean it with? It seems to get mungy after several uses... More questions: How often should the glow plug be replaced with a new one? How do they typically last? Should I a have a stash of extras? Thanks again ahead of time...

I have never seen castor oil gum up a plug either, I fly about 98% RC and the rest CL. The only times I have fouled a plug is when breaking in the engine and running too lean. When running rich the raw fuel actually seems to clean the plug, not foul it. Though the face does turn darker, the important part, the wire, stays clean and bright.

No. With the proper treatment and air/fuel mix, a plug should last a long time with no maintenance.

It's ok for the plug to discolor. If it's getting "mungy"(?), the I'd suspect the mixture is wrong. The element should be clean and not fouled with deposits. Nor should it be whitish and "burned-looking". In the first instance, your mix is too rich. In the second, it's too lean.
Dr.1 Driver
"There's a Hun in the sun!"

On my GS.45ABC, if I ran it rich (using only castor oil in the fuel, as per the racing regs here), it would gum the plugs up in short order. Lots of dark crap around the face of the plug and in the recess where the element is. I got a lot longer out of a plug if I ran it leaner, but not too lean of course.

Mind you, do you idle your G51 at all? My .45 would run perfectly fine at full noise (rich) with the gummed up plug, but wouldn't idle worth a damn.
Didn't even want to run below about 1/4 throttle, unless I changed the plug for a new one. All would be well again, until the plug gummed up. After it was fully run in, I didn't run it that rich anymore, so no more gummed plugs.

Hi there, Depends what you mean by 'mungy'. If you mean you're getting loads of dark crud all over the place, it's probably due to running too rich and/or having castor oil in your fuel. Even with castor though, it shouldn't 'gum up' after only a few flights......most likely, it's just too rich. On the other hand, if the element is 'frosty' and white, you're running way too lean. The element should stay clean and sort of shiny.

The best way to know if you need to replace the plug is to observe what happens when you remove the glow clip after you start the engine. Taking the plug out of the engine all the time is *not* a good idea......sooner or later, you'll end up with stripped thread in the head, unless your engine has a brass thread insert and not just plain alloy threads (don't ask me how
I know). If you remove the glow clip and the engine loses lots of revs and/or stops, your plug is buggered. This is assuming the engine is tuned correctly of course. The 'losing lots of revs' thing is also a symptom of a too rich idle mixture. Commonly, the engine will 'load up', slow down and splutter to a stop. However, if your engine is tuned ok and it stops when you pull the glow clip off, the plug is finished. Basically, it means the platinum in the element is no longer sufficient to keep the plug glowing without the aid of external power.

How long a plug lasts is determined by how you treat it. Lean runs kill plugs in short order......one lean run is often enough to ruin a plug (bad idle behaviour etc). Running too rich is nowhere near as bad, but will still eventually 'gum up' a plug, particularly if you use castor oil in your fuel. I've got a couple of 4-strokes (YS .91FZ's) that have the original plug still in them after more than 12 months of regular use. Still run perfectly. If you look after them, the plugs should last ages.

It's always handy to have some spare plugs in your field kit. Nothing worse than having a plug finally die (after endless months of fault free service)
and not having a spare! When I'm getting down to my last couple of spares,
I buy a whole card of new ones......keeps me going for a loooooong time and means I've got some left in case some unfortunate soul doesn't have a spare at the field

Straight fuel (no nitro), 4:1 methanol:castor mix and the standard muffler that came with the engine.