Temp light coming on intermittently, mk2 jetta

[Diesel_Zuk]

1991 ecodiesel, light has been coming on immediately after starting in the morning. Ebgine is still cold. I've checked the antifreeze level, it's good. I shut it off and restart, and it goes away. 30 minutes later, comes on again, shut it off, restart, and it doesn't come back on for rest of my commute. I'm guessing it's nothing major, because it's been happening for about a month now, mileage is still 40 mpg, coolant level still good. Any ideas where to start?

[vanbcguy]

Is it on steady or flashing?

[Diesel_Zuk]

Flashing. I unplugged it and plugged both sensors coming off the head, then treconnecter, and it didn't happen for about a week, but it's now doing it quite often.

[Patrick]

If it's flashing it's probably telling you that there is water in the seperator ahead of the back wheel.

[Diesel_Zuk]

If it's flashing it's probably telling you that there is water in the seperator ahead of the back wheel.

What's that mean? I seriously don't know.

[vanbcguy]

The water separator will flash the glow plug light, not the temp light.

Either you've got a wiring issue somewhere, the probes in the coolant reservoir are bad or your cluster is having issues. Start with the wiring, I had the same problem with mine. In my case the solution was to re-pin the connector at the coolant ball, it was not making a good connection.

[Patrick]

I stand corrected. Mine hasn't done it in a long time.....

[air-cooled or diesel]

check,clean up contacts. the radiator fan switch is at the bottom of the radiator drivers side, check, clean up. i found when this was happening to me , years ago, it was the reservoir sensor, i ended up getting a new reservoir. i use electronic spray for contacts. could be a just low water level? or a restriction , check reservoir return flow, dont let it boil over while checking.

[Diesel_Zuk]

check,clean up contacts. the radiator fan switch is at the bottom of the radiator drivers side, check, clean up. i found when this was happening to me , years ago, it was the reservoir sensor, i ended up getting a new reservoir. i use electronic spray for contacts. could be a just low water level? or a restriction , check reservoir return flow, dont let it boil over while checking.

I don't think it's low, but I guess it is possible. I haven't checked it in a little while.

[fatmobile]

Bad ground on the resevoir sensor?

[Diesel_Zuk]

Just checked coolant level. My overflow tank is so dirty I cannot easily see a line of where the level is, but I think it looks full. It seems odd that if it was just low, that it would only come on at times, and not always on.

[vanbcguy]

Actually that's not surprising at all. Once it detects a low level it latches on until the car is shut off. A quick turn, steep hill or heavy braking or acceleration can slosh the coolant around enough to trigger it if the level is just a bit low.

Also, if your coolant bottle is nasty then there is a good chance the probes are filthy too, making a good connection difficult.

[Diesel_Zuk]

I unplugged the things again on the head, and noticed they felt wet, not sure what from, but I left them to dry, and light hasn't come on since. Not sure if it was just low or what.

[air-cooled or diesel]

hit contacts with electronic spray and let dry, may help.

[TimpanogosSlim]

hit contacts with electronic spray and let dry, may help.

Yup. CAIG De-OxIt DN5 spray. amazing what it'll fix.