VR6 cooling problem.

[KarmannVR6 0]

Just done a search, cant find anything.

 

Reacently changed the thermostat housing due to leakage and replaced the thermostat while i was there. The car ran ok for a week or so untill yesterday when the temp gauge went of the chart and the coolent light started flashing. I left the car for a couple of hours and started it again but the temp was still of the chart even though the coolent was cold.

 

Now the temp gauge dosent even move but the light still flashes.

 

Any Ideas?

[Roger Blassberg 0]

The light is not a temperature sensor, but simply a level indicator in the header tank.

 

It sounds as though you have an air lock in the cooling system which is causing all sorts of spurious readings/signals.

 

When you refilled the system after the thermostat change, did you disconnect the top hose from the radiator end pour the coolant in through it into the block; if you just connect it all together and pour coolant directly into the header tank you risk getting air trapped in the system.

 

Best wishes

 

RB

[KarmannVR6 0]

Thanks for the reply. Yes i refilled it through the header tank. Do you know the best way to get the traped air out?

[RW1 0]

You have an electrical fault. That symptom usually occurs when the temperature sensor or the signal wire to the dash guage has grounded somewhere. Check the wires and more likely, check the sensor for a short on the pins.

[Roger Blassberg 0]

To check if it is an air lock or a coolant level problem, does your heater supply hot air properly and is the coolant level correct in the header tank? If not I would disconnect the top hose from the radiator and the cap from the header, then pour coolant into the hose until it runs out, reconnect and then top up the header.

 

It could well be an electrical fault as RW1 says; you may have disturbed a wire when doing the thermostat job.

 

Best wishes

 

RB

[KarmannVR6 0]

Thanks for the advice guys. Coolent level is ok but the heater isnt blowing out hot air, just warm i would say.

 

I'll get to work on the air lock but as for the electrical fault i have tested the resistance of the blue and black sensors and im getting no reading. Is this normal?

 

Also what are the for: Blue Black Yellow?

[Supercharged 2]

All the senders should show resistance weather they are hot or cold - test them again, they can't all be dead!

[KarmannVR6 0]

ok, i just tested all three sensors with the multimeter. The yellow four pin sensor seems to be ok as does the blue two pin sensor. The black one is giving me no reading, so i guess its shot.

 

What is the black one for?

[Roger Blassberg 0]

I thought it was something to do with air conditioning - do you have that?

 

Have you also checked the wiring and connector continuity.

 

Best wishes

 

RB

[KarmannVR6 0]

No i dont have air con. Checked the wireing, seems to be ok.

 

Any ideas if this black sensor is the cause of the problem?

[Roger Blassberg 0]

Try swapping the connectors between blue and black sensors to see if that brings your temp gauge back into the land of the living - I think that the sensors are both essentially the same. If the black sensor is dead it will fail to give the ECU the correct water temperature info and your start-up may be a bit difficult due to this.

 

If the level in the header is correct, then there should be no flashing light. The level sensor is very sensitive, so even a cm. or so below will set it off

 

Sensors are cheap, probably less than £10; if you replace one make sure you change the rubber o-ring as well.

 

Just in case you didn't know, use G12+ coolant to be on the safe side. G11 and G12 react with each other to form a cloggy mess, G12+ does not and is safe to mix with either of the other two.

 

Best wishes

 

RB

[KarmannVR6 0]

Thanks for all the advice folks.

 

Gonna replace the sensors and see what happens.

[Roger Blassberg 0]

You are welcome.

 

Please be sure to let us know what the outcome is.

 

Best wishes

 

RB

[Henny 0]

I thought that Black was for the gauge, Blue was for the ECU and yellow wasn't used unless you had air-con?!?

 

Dead gauge and dead black sensor would seem to back this up too...

 

Check that your water level IS spot on in the header tank, it doesn't need to be a lot lower for it to put the light on. You may wish to test that it's not a wiring fault by disconnecting the multiplug on the header tank and seeing if there's any difference on the dash. You could then short out the 2 pins in the wiring connector and see if that makes the light go on/off (don't know if it's designed to make contact if it's too low, or if it's correct)

 

Good luck! 8)

[Roger Blassberg 0]

The Gospel According to Mr. Bentley shows as follows; blue 2 point sender to ECU, yellow 4 point sender to control fan run-on and aux water pump, black (if fitted in place of blanking plate) for aircon.

 

So where the h**l is the gauge sensor??

 

I feel a Kevhaywire moment is needed at this point...........

 

Best wishes

 

RB

[Kevin Bacon 5]

One way of checking would be to connect VAG-COM and disconnect all 3 senders in turn (with the ignition on) and see which one kills the coolant temp signal when looking at the measuring blocks.

 

However, AFAIK, 2 of the 4 pins on the yellow one feed the aux pump controller (fans run from the radiator thermo switch) and the remaining 2 feed the temp guage.

 

There are no other senders on the engine other than those, oil pressure/temp and the rotational and knock sensing ones, so it has to be the yellow one, assuming the black one is a 'dummy' on non-air conned engines.

[RW1 0]

OK, offside to nearside on thermostat housing. Yellow is dual - 4 pins. Radiator fan control & dash temperature gauge sender.

Pins 1 & 4 are the radiator fan (thermoswitch). Pins 2 & 3 are the dash temp sender - reasonable resistance (variresistor). Wiring colours are different for each model year.

 

Middle sensor - blue 2 pins, is the ECU temp sender.

 

Nearside is a blank unless Aircon is fitted. If fitted it is a 4 pin brown sensor.

[KarmannVR6 0]

Coolent level in the header tank is just below the max mark so something else must be making the light come on.

 

My C dosent have air con but does have the black 2 pin sensor. Took it out and tested it but got no reading so im thinking its broke.

 

I got the part number off it and ordered a new one from the stealer.

 

Should be here friday, so i'll let you guys know the outcome.

 

Thanks for all your advice.