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General Information => Troubleshooting => Topic started by: Diesel_Zuk on October 22, 2014, 07:11:16 pm

Title: Temp light coming on intermittently, mk2 jetta
Post by: Diesel_Zuk on October 22, 2014, 07:11:16 pm
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?
Title: Re: Temp light coming on intermittently, mk2 jetta
Post by: vanbcguy on October 22, 2014, 08:57:53 pm
Is it on steady or flashing?
Title: Re: Temp light coming on intermittently, mk2 jetta
Post by: Diesel_Zuk on October 23, 2014, 07:58:43 am
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.
Title: Re: Temp light coming on intermittently, mk2 jetta
Post by: Patrick on October 23, 2014, 01:22:53 pm
If it's flashing it's probably telling you that there is water in the seperator ahead of the back wheel.
Title: Re: Temp light coming on intermittently, mk2 jetta
Post by: Diesel_Zuk on October 23, 2014, 08:57:41 pm
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.
Title: Re: Temp light coming on intermittently, mk2 jetta
Post by: vanbcguy on October 24, 2014, 08:10:06 am
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.
Title: Re: Temp light coming on intermittently, mk2 jetta
Post by: Patrick on October 25, 2014, 04:10:19 am
I stand corrected. Mine hasn't done it in a long time.....
Title: Re: Temp light coming on intermittently, mk2 jetta
Post by: air-cooled or diesel on October 27, 2014, 04:22:23 am
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.
Title: Re: Temp light coming on intermittently, mk2 jetta
Post by: Diesel_Zuk on October 27, 2014, 03:15:30 pm
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.
Title: Re: Temp light coming on intermittently, mk2 jetta
Post by: fatmobile on October 28, 2014, 12:51:49 pm
Bad ground on the resevoir sensor?
Title: Re: Temp light coming on intermittently, mk2 jetta
Post by: Diesel_Zuk on October 28, 2014, 07:02:06 pm
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.
Title: Re: Temp light coming on intermittently, mk2 jetta
Post by: vanbcguy on October 28, 2014, 08:21:39 pm
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.
Title: Re: Temp light coming on intermittently, mk2 jetta
Post by: Diesel_Zuk on October 31, 2014, 09:54:11 am
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.
Title: Re: Temp light coming on intermittently, mk2 jetta
Post by: air-cooled or diesel on October 31, 2014, 03:21:08 pm
hit contacts with electronic spray and let dry, may help.
Title: Re: Temp light coming on intermittently, mk2 jetta
Post by: TimpanogosSlim on October 31, 2014, 11:10:42 pm
hit contacts with electronic spray and let dry, may help.

Yup. CAIG De-OxIt DN5 spray. amazing what it'll fix.
Title: Re: Temp light coming on intermittently, mk2 jetta
Post by: Blocksmith on December 04, 2014, 01:40:39 pm
My brother's mk2 does this intermittently, and I've found that cleaning the probe ends in the overflow tank resolves the issue, at least until they get dirty again. And like Vanbcguy said, if your coolant tank is dirty enough that it's difficult to see into (like the one on my brother's car), there's probably sludge in the coolant system that's built up on the probe.