Glow Plugs and Dash Light

[dougand3]

My dash gp light used to light for 10 secs for many months, then for 5 secs for a few months, then recently no light. Found all 5 gp's were dead.

Today, I changed out glow plugs (and as most have said...it's hard as hades - "inventing" socket tools, wobble extensions, pliers, losing nuts)

The 300SD now starts great. And the gp dash light illuminates again....BUT only for 3 secs. When I listen to the relay click - the cycle is always 28 secs.

Why the different gp dash light times? Is there some cylinder temp feedback to gp relay? Or is this one of those 617 "things"?

Thanks, Doug

The GPs always glow for the same amount of time (usually about 40 seconds), but the time of the light is controlled by temperature (usually at least 10 seconds when cold). Your times seem a little short, maybe the relay is acting up.

[dougand3]

Thanks, Craig. I'll just watch how it behaves in various outside temps.

[Dee8go]

I always assumed that the period of the glow plugs warming up would vary depending upon the ambient temperature. Are you saying that they do this for 40 secs all the time?

Originally Posted by Dee8go

I always assumed that the period of the glow plugs warming up would vary depending upon the ambient temperature. Are you saying that they do this for 40 secs all the time?

Yup, the dash light varies with the engine temperature, the timing of the GPs is fixed. Unless you have a post-glow relay, they will time out in about 40 seconds (try it and listen for the click or watch the dome light) or the will shut off when you crank the engine. If you have the post-glow relay, they will stay on for about 3 minutes after the engine is running.