Thread: quick inquiry.

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Is there a difference between a spark plug and glow plug?? Sorry to bother such a stupid question.

Yes, one glows and one sparks.

a spark plug sparks when the ignition fires...a glow plug is for diesel engines. This response is over simplified...but I'm overly simple..

A glow plug provides a concentrated point source of heat to ignite diesel when the engine is cold. Once running, the heat of combustion and residual heat in the cylinder ignites the fuel/air charge on compression alone. Carbon deposits in a high mileage gas engine can cause similar hot spots, causing the gas engine to "run on" or "diesel" after the ignition is shut down.

Glow plugs for diesel don't ignite the mixture---they are not located in the combustion chamber

Glow plugs however are used on model airplane engines to lite off the initial fuel mixture and build up heat before disconnect

And jet engines for lite off

Originally Posted by jerry clayton

Glow plugs for diesel don't ignite the mixture---they are not located in the combustion chamber

Glow plugs however are used on model airplane engines to lite off the initial fuel mixture and build up heat before disconnect

And jet engines for lite off

Jerry, you're 100%. My description is more for jets & models. In the diesel they pte-heat the block.

Actually some diesels do have glow plugs in the chamber. Usually lower compression, gas engine-based automotive diesels.
Field-Marshall two-stroke single cylinder diesel engine had a wick! You got a cigarette-sized roll of nitrate-treated paper burning and screwed it in a hole like a spark plug hole, and cranked her up! It could also be started by firing a shotgun shell in a little chamber with a BFH, but that's another story.

Originally Posted by R Pope

It could also be started by firing a shotgun shell in a little chamber with a BFH, but that's another story.

Brings back memories of the old Flight of the Phoenix movie - six shells to use, and the engine lit on the last one. High drama, that!!

......and I can assure you in cold weather a diesel WILL NOT start without glow plugs - as I can relate when my tractor wouldn't start last winter after a snow storm when the beasties that camped out in the engine compartment thought the glow plug the insulation was better food then scrounging some spilled bird seed. Killed all three glow plugs plus a chipmunk who was still there when I tried to start it up to use the blower.

Now - if I could have used one of those starting shotgun shells

Originally Posted by IC2

......and I can assure you in cold weather a diesel WILL NOT start without glow plugs - as I can relate when my tractor wouldn't start last winter after a snow storm when the beasties that camped out in the engine compartment thought glow plug the wire insulation was better food then scrounging some spilled bird seed. Killed all three glow plugs plus a chipmunk who was still there when I tried to start it up to use the blower.

Now - if I could have used one of those starting shotgun shells

used to have a diesel rabbit - always ate glow plugs.
many times started it with lots and lots of hot water
poured over the cylinder head.

I've worked on diesels my whole life..... a few corrections here:

Mr Clayton, glowplugs are often in the combustion chamber. Indirect injection diesels have a seperate combustion chamber with the glowplug and injector in it.

Many diesels can start without glowplugs. It is all dependant on the style of injection, combustion chamber, etc. Many direct injection types will light off just fine with no glowplugs. Many of the engines I work on will have block heaters and other forms of ignition assistance but will often fire off just fine with nothing. (2 stroke detroit diesels are a fine example).

Tool, old VW's, internationals diesels, and many Indirect injection type would eat/destroy glowplugs if the fuel injection timing is way too advanced. The combustion is so instantaneous that it'll shatter/erode the glowplugs.

Drew

Kinda think of a glow plug as a sparkplug that has a full time low level fat spark. Nope, not a good analogy , try a glowplug is like the element in your electric oven. It provides a glowing heat source for starting as long s electricity is supplied to it. Running the plugs in a warm running engine will quickly destroy them.
Tip for starting your diesel in cold weather. Remove he air filter and direct air from your knipco or other larger heat source into the intake tract. Diesels rely on heat from compression to run and warming the air makes it easier for this to occur.