Coolant Light Woes

[total stranger]

Hmmm, this is the thing.  I replaced the thermostat when I replaced the water pump.  Do you think that is what is causing the water temp gauge to go the third line?

Seems a possibility. If the temp sits stable at that  point then maybe the stat is set for the wrong temp.

[robw09]

I changed the black temp sender and will see if there is any difference.


The pump and thermostat was done by local garage.

I presume it is this one?  For 6 quid I might just do it myself.  It is by the water pump and I have to move the power steering pump out of way to get to it?  Also noticed a small leak from the coolant flange going into the head.  So, will have to get a O ring for that.  Is that the second link?
 

https://www.vwheritage.com/shop/056121113D/thermostat-inc-gasket-mk1-2-golf-scirocco-corrado-1500-180/#esp_cf=years&esp_filter_ESP_Rational_vehicleAliases=MK2%20GOLF&esp_filter_years=1990&esp_pg=1

https://www.vwheritage.com/shop/037121687/o-ring-for-coolant-flange-t4-90-03-mk1-mk2-golf/

[total stranger]

Before doing anything please read and re read the guide by rubjonny that has been linked to earlier in this thread. The thing most people miss is resetting the ecu after changing the sender.

Your links look right to me.

From memory the stat is at the lower front left of the lump as you stand in front facing away from the car, I did one laying on the floor without jacks once.

[robw09]

I did follow the guide, should have said that sorry.  However, I could not see anything about resetting the ECU??

But do you mean for the blue sender or do you do this for black as well??

"Once the new sensor has been installed, start the engine and disconnect the blue coolant temperature sensor.
Rev the engine through 3,000 rpm three times, each time allowing the throttle to close completely.
This clears the Digifant ECM fault memory."

[total stranger]

ECM or ECU both mean the same.

Quite frankly I don't know as I haven't replaced the black one. I cant see it hurting though man.

[robw09]

So, changed the black sender and reset the ECU.  Guess what?!?

It seems to have worked.  I suspect it now to have been a faulty (replacement) sender.

Temp comes up to just below 2nd line now (just under half way) and stays there under driving conditions.  Bottom rad is still cold.  I then left car ticking over on the drive and the temp rose to the line at which point the bottom hose got warm (presumably as the stat opened).  I get no lights flashing.  So, all appears ok now.  Not had chance to check the fans spins up, but pretty confident it will as it was before hand.

Thanks everyone for helping.  I am off to change the sump & do a service!

Balls.  Spoke too soon.  Temp fine, but light comes on after about 15 minutes driving and then pretty much stays on with it only occasionally going off.  This is bloody frustrating as everything points to it being fine now.  Gauge only goes between below the 2nd line and just on it.

Could it possibly be the sensor in header tank?  Mine has the built in type so it would need the whole tank replacing.

Rob

[total stranger]

At this point I am out of ideas man.