How does the cold kill glow plugs?
 

Glow plugs work fine and start our diesels but when temps go down to 2 degrees, the cold zaps the glow plug and they go bad. Why doe this happen? If the weather then turns back warm, do these glow plugs remain bad after the cold zapped them? Curious to your thoughts, thanks.

Becuase the glow plug relay keeps them on for a longer amount of time in order to heat up enough to start the engine.

Have a great day,

Also when it is warmer, the car will likely start with one, and maybe two glow plugs out. When cold enough it will not start with any of them out.

The glow plugs are a resistance coil of some shape or other inside the steel tube. The longer they run, the hotter the coil gets, and eventually it will sag or twist and weld to the side of the tube. It will still heat, but the tip of the plug doesn't get hot anymore, so the engine is hard to start. Champions will break the filament off the tip weld, leaving a nice little hole.

Once the GPs are bad, they stay bad.

Peter

You might ask: Why do common light bulbs give out earlier in cold climes vs. warm?

The reason: Too many cycles combined with too harsh starting temperature conditions.

That is why there is there are less glow plug failures in FL. vs. VT. Glow plugs are, after all, only filaments.

Very interesting, thanks guys. "I see," said the blind man.

Yeah, I learned that lesson in Canada -- you had to buy top dollar headlight bulbs, or the temp extremes caused the filament to break early -- -40F to incandescent two or three times a day is rough on that little wire....

Peter