What determines how long glow plug light stays on?

[motomike33y]

 In my 91 jetta NA the glow plug light on the dash stays on about 40 seconds.  I have a relay w/ #60 which, I understand is the medium fast relay.  But..., I tried several other relays from my old 82 rabbits, and the time is still the same.  The plugs glow w/in a few seconds when power is on, because I checked before putting my injectors back in a couple months back.  I haven't hooked up anything to check lately to see if power is on all the time the light is on, but previously when I've checked, it did.  Even when the vehicle has been running, and I shut it off, the light will come on when I turn on the key-my vanagons used to not come on if the engine was warm, and I don't think the rabbits did either.  So, maybe bad tem sender?  How to check?  other suggestions?  thanks. 

[burn_your_money]

Sounds like a broken wire or bad sender. Swap the 2 plugs on the 2 sensors on the coolant flange. If the light stays on for a shorter amount of time and the temp gauge doesn't work then you've just figured it out.

[Vincent Waldon]

Yup, 40 seconds is pretty much the "as long as possible" time for most relays.

Your relay thinks it's really cold out... so as Burn says, either a dead coolant sender or an issue with the wiring between the sender and the relay.

[vwjunkie53]

If the sensor doesn't cure the problem, I would ohm out all your plugs.  I had a weird problem with my engine, all of a sudden the gp light would stay on for much longer than you would expect, even on a warm morning in the summer when it would have normally only lit for maybe 5 or 10 seconds.  It turned out one of my glow plugs had gone bad, but still had resistance rather than having no continuity.  The ohm reading was super high, and for some reason that extra load on the relay made it stay on for a long long time.  I changed the plug and it was back to normal.

Just a thought.

Jason

[bajacalal]

Have a look at the connector for the sending unit. For one thing it's one of those weird button type plugs that loosen easily, it's 20 years old and diesel engines vibrate a lot. It probably isn't making good contact anymore.

[motomike33y]

coolant flange has two two wire plugs coming out, so can't easily try that.  I'll check out the fastener, then see if I have another sender around.  Any differences between the one pin sender unit for this and various other temp senders(same type of connector)?

[burn_your_money]

Aren't the 2 wire style conenctors both the same?

I think there are some ohm vw temp specs in the bentley for testing them

[motomike33y]

nope, the one on the end of the head is the slide-over single wire, and the two on the front of the head are each brown wire plus two colored wire going into a plug(2 separate plugs ie 4 wires) which goes into the flange coming out of the head.

[bajacalal]

the one on the end of the head is the slide-over single wire

IIRC that is the one which controls the glow plugs.

I'm not sure how different the wiring is across model years but I think it's fairly similar.

[burn_your_money]

I was thinking that one was for the A/C.

Are the two on the front of the head interchangeable?

[motomike33y]

yes, it has non-working ac, so both plugs on front are the same-just different colored wires

[burn_your_money]

That's debatable. Some say the same, some say slightly different. They are close enough to be interchangable though.

[motomike33y]

I'll try switching them, but I had placed them based mostly on wire length