# MK2 running hot



## in5ane (Dec 17, 2004)

*MK2 "overheating" must have read each related thread thrice*

ok so, my "new" 89 Wolfsburg has run its temperature up to 3/4's on the gauge consistently and stays there without any other issues.

I have just had the shop replace the thermostat when timing belt was being replaced last week.
Shop confirmed water pump is in perfect running order.
I have replaced the cracked coolant expansion tank, no longer any fractures and no signs of leak.
When burping the coolant system on last top up, the coolant was flowing free and clear.

I cannot seem to get the temp to sit at half the way it sits between 5/8's and 3/4's :banghead:
My only other thought is that the gauge is just incorrect. 
Tomorrow my next step is the Coolant Temperature Sender/Sensor (black) 
...could this sensor alone cause this issue? Zero warning lights, no CEL
other thoughts...??


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## in5ane (Dec 17, 2004)

*Update*

After a long enough drive and getting the car back to its usual 3/4 heat, i pulled over and felt the bottom hose of the rad and its completely cold while everything else looks normal.

Is it possible I'm dealing with just an air pocket seeing as how thermostat is new?
Bad Rad?
Should I be concerned that the fan doesn't seem to be kicking in or is this because the rad isn't flowing and therefore isn't hot??


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## in5ane (Dec 17, 2004)

*another update*

when changing out the temperature gauge sender, coolant did not just drip out, it flowed and would have continued flowing if not plugged.

This is with the overflow cap off and a cold engine. Haven't swapped new sender/sensor in just yet, does this overflow indicate trapped air? I've been burping this thing repeatedly and the level never dropped (until I pulled the sensor)

HELP


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## L33t A2 (Aug 5, 2003)

*FV-QR*

sounds like your new thermostat is faulty


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## in5ane (Dec 17, 2004)

L33t A2 said:


> sounds like your new thermostat is faulty


thanks for the only response so far
wouldn't a bad thermostat cause my in-car heating to act up?
I have full heat at all speeds/temps and no a/c to test around with...

another update: found out that the lower rad hose will EVENTUALLY warm up


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## in5ane (Dec 17, 2004)

temp gauge sender now also replaced with the same results..."overheating" on the cluster

this time once the needle pegged almost all the way to the right, we shut er down and popped the overflow tanks cap. Stuck in a cheap meat thermometer and it read about 165 degrees (mind you thats from the tank, not the block.
Is this a high temperature??

Coolants still flowing well. Still no issues with heat in the cabin
I've narrowed it to radiator flow or simply a bad cluster


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## L33t A2 (Aug 5, 2003)

*FV-QR*

If the thermostat is good, it is supposed to open and regulate the temperature at 87*C/189*F.
Coolant flows out the front of the cylinder head and attempts to enter the radiator.
When cold, the thermostat is closed, so no coolant can pass through the radiator.
This leads the coolant into the hose that goes down the front of the block and into the side of the water pump until hot.
The heater core gets its own direct flow from the side of the cylinder head at full temp.
This cycles through the heater core and then travels through the metal coolant pipe to enter into the side of the water pump.
Once the thermostat opens, coolant flows into the radiator and gets cooled either by ambient air flow, or with the assistance of the rad fan.
Once this happens, the lower coolant hose should get pretty hot, but since the coolant was cooled by passing through the radiator, the lower hose won't technically be as hot as the upper hose.
The coolant flange on the front of the head has a couple sensors, the blue one is for the ecu, the black one is for the gauge cluster.
The fan is controlled by a coolant temperature switch, located in the radiator on the lower driver's side.
Additionally if the car was equipped with A/C, there will be a mess of relays regarding the activation of the fan when any of the HVAC controls are set to A/C, including defrost mode.

I like to let the car idle up to temp while keeping my eye on things, this may take a very long time. Sometimes I hold the RPM around 2000 for the majority of this. Idle up to temp, periodically reaching down and grabbing the lower hose by hand to see if its hot. Obviously be careful not to let ANY loose clothing or fingers get near the belt assembly or near the fan blades. The lower hose should get pretty hot, hot enough to burn your hand, and then the fan should turn on. Stock fan switch turns on low speed at 95*C/203*F and run until it cools down to 84*C/183*F
Side note: High speed turns on at 102*C/215*F and runs until it cools down to 91*C/196*F at which point it switches back over to low speed range.
If you can find it in your budget, pick up an infrared thermometer, they run $20-25 currently at harbor freight.
Overheating begins above 215*F


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## in5ane (Dec 17, 2004)

Thanks again
I understand all of this and really am leaning towards a faulty gauge/cluster

There's no way temp gauge should be 7/8s full and the fans aren't on, rads not warm, zero evidence of that kind of heat.


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## in5ane (Dec 17, 2004)

OK, rad and entire cooling system is fine as verified by mechanic.
The gauge is just way off.

Could be bad ground wire somewhere but nothing is actually overheating

It did just occur to me that the PO had a stereo because when he removed it, the wiring kit ends were left loose in the trunk. 

I've capped the wires for now, does this create an open circuit tho? 
Unrelated?


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## ziddey (Apr 16, 2006)

in5ane said:


> when changing out the temperature gauge sender, coolant did not just drip out, it flowed and would have continued flowing if not plugged.
> 
> This is with the overflow cap off and a cold engine. Haven't swapped new sender/sensor in just yet, does this overflow indicate trapped air? I've been burping this thing repeatedly and the level never dropped (until I pulled the sensor)
> 
> HELP


Nope, it indicates you took the overflow cap off.



in5ane said:


> this time once the needle pegged almost all the way to the right, we shut er down and popped the overflow tanks cap.


Don't do that.



Does your fan ever kick on? Low speed? High speed? 

As far as "burping" goes, I've always just driven around for a short while with the cap on but not tight. Our setups aren't really prone to air pockets.


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## in5ane (Dec 17, 2004)

No if u read my last update the fan is working and all is well minus the gauge. 
U quote me out of context. I go on to mention the actual temp was 170 or so

Car has been runnin with temp gauge maxed and u can hold the coolant hoses in ur hand without getting burned. 
Faulty gauge in the cluster or a bad short somewhere.


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## Fat Rabbit (Nov 18, 2001)

Since the temp guage is a thermal resister (thermister) unexpected resistance in the wiring between the sensor and the gauge can cause readings to be off. A bad gauge in the cluster can also cause and issue as can a bad voltage stabilizer in the cluster (although that will also effect other cluster functions). The wiring is easy enough to check. The cluster can be repaired or replaced. But as long as all is well and you know what is going on there should be no issue with just leaving it. I have run into a lt of VW temp gauges that have read high or low. FR


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## in5ane (Dec 17, 2004)

Fat Rabbit said:


> Since the temp guage is a thermal resister (thermister) unexpected resistance in the wiring between the sensor and the gauge can cause readings to be off. A bad gauge in the cluster can also cause and issue as can a bad voltage stabilizer in the cluster (although that will also effect other cluster functions). The wiring is easy enough to check. The cluster can be repaired or replaced. But as long as all is well and you know what is going on there should be no issue with just leaving it. I have run into a lt of VW temp gauges that have read high or low. FR


thank you, it will just take getting used to seeing the gauge that high. I can inspect the wiring closely however the PO didn't exactly leave the engine bay clean and tidy


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