I have a couple of questions about the glow plug system. The car starts and drives fine. But sometimes the glow plug dash indicator blinks after start up and it also only stays lit for approximately 2 seconds. I recently tested the glow plugs and they tested fine. I replaced them any way and bench tested the new plugs prior to install. I believe that the glow relay is the culprit but I am not sure. I guess my questions are
1) How long should the dash light stay lit?
2) When the dash light goes out should the plugs still be getting voltage?
3) Is there a test procedure for the plug relay?
4) Would the blinking dash light be an indicator of a bad glow plug relay?

Thanks in advance.

Here's a good link that explains how to test the entire glowplug system. I found it very helpful.

http://dieselgiant.com/glowplugrepair.htm

Let us know how you do.

Bert

that is the same basic test procedure that I used everything test ok but I still only get about 2 seconds of dash light and it blinks (sometimes) after start up
Thanks

I hope for your sake that your car can take one of the new Bosch upgrade Relay Kits that run about $100... otherwise you could be looking at over $200 for a replacement relay.

IF you are facing an expensive relay replacement, another option is to change over to a much simpler relay system that is far less expensive and more reliable. With such you would manually operate the glow plugs using either a spring loaded or push button switch on/under the dash. It uses an very simple and thus reliable relay. Let us know if you want more info on this upgrade to an old style system.

On a lark I recommend you remove the fuse on your relay and then re-install it. This can some of the time show that your fuse has "embrittlement" and needs replacement. It can cause your relay to act up and nor work also.

Good luck,
Sam

Good pointers from respondents.

My glow plug light blinks now and then. It has been doing this for years.
Coincidentially, it blinks more when there is moisture in the air.

The real purpose for the blinking is to warn you that a glow plug is weak. But then again, gremilins!

__________________
1979 300D 220 K miles
1995 C280 109 K miles
1992 Cadillac Eldorado Touring Coupe 57K miles SOLD
********************
1979 240D 140Kmiles (bought for parents) *SOLD.
SAN FRANCISCO/(*San Diego)
1989 300SE 148 K miles *SOLD

Thanks for all the input. I was able to find a used relay fo 45.00 so that will at least give me one to play with. To answer the question as to the new bosch kit that would be no the wiring harness is different. The manual idea sounds intresting. Point me in the right direction please. I would like to make the original work because this is my wifes car and I am not sure if she would go for that. She isnt very daring when it comes to her baby!
Thanks again

one more thing
the realy does cut voltage to the plugs at about 25 seconds but the dash light goes off at about 2 seconds.
Cant find a good electrical schematic but I was under the impression that the dash light indicated that voltage was being supplied to the plugs. Is that wrong?

to the best of my knowledge... is MBZ/Bosch's designed-in "guestimate" of just how soon you can actually try to successfully crank over the engine... based upon temperature sensors on the engine block and on some models I think there is actually an actual air temperature sensor. Leave it to the Germans to over-engineer such things.

As to the manual up/down-grade old fashioned relay kit, you can find one version by going to www.**************.Com and then use " manual glow plug relay ". His are a bit pricey so you might want top "Google-around" for a better price. I think there is remember a THREAD on this FORUM's WebSite.... hmmmm... here it is:
http://www.peachparts.com/shopforum/showthread.php?t=155464&highlight=%22manual+relay%22

Ain't this FORUM great!!! They get as much of my parts business as "practicable" from now on!

Regards,
Sam

The relay does continue to power the glow plugs after the light goes out. On my cars the plugs are energized for about 40 seconds (you can hear it click and see the dome light change). The amount of time the light stays on is just a guide to tell you when to start the car.

When my GP light started acting up a few years ago, I just replaced the relay and the problem went away. I would resist the temptation to hack up the system and make it manual, you may actually want to sell the car someday and some future owner will just have to fix it correctly.