Glow plulgs cycle after engine is started?? Why

[rdragoo]

My glow plugs seem to cycle once or twice briefly during a cold start after the engine has already began running. Is this normal? What tells the glow plug controller that the engine is running and GP operation is no longer needed? thanks to the group.

 

[mangus580]

Very much so normal. There is a temp sensor, as well as time.

 

[mangus580]

oh.. missed the why part. To assist in warming the combustion chamber and eliminate unburned fuel.

 

[rdragoo]

That all makes sense. I guess I was worried that GP operation with the engine running would damage the glow plugs.

 

[ARMYMAN30YearsPlus]

Mine Cycle in both my 6.2 CUCV and my 6.5 Suburban with no ill effect, Mike hit this right on the head as the plugs are designed to withstand the extreme temps and pressures of combustion. If they stayed on without regulation that would be bad as they draw a lot of current and they would burn out.

 

[CUCVFAN]

It was almost a "cosmetic" thing to help reduce the white smoke on start-up by warming the chambers up quicker. Civilian trucks do it too.