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2002 Passat V6 overheating. Check my troubleshooting

8K views 21 replies 7 participants last post by  PZ 
#1 ·
Hi Guys!

I am the original owner of a 2002 Passat V6 with 254,000 mileage. Thanks to this forum my goal is to get over 400,000 out of this wonderful little German.

I have reviewed posts about overheating and I would like to know if I am on track to repair this issue. On Friday the temperature guage shot through 190 degrees or the 12 o'clock position heading to the red. I turned on the heat to high and this brought the guage down to about 210 degrees so I was able to get home. This was first drive in the morning.

The fan clutch was weak and the original so I replaced with a Miely from ETS. This did not solve my problem. The water pump was was replaced at the last TB change at 170,000 miles at the VW dealer. Last October I changed out the overflow bottle. I have no coolant leaks. The CTS was replaced at 237,000 miles. I have always used the G12 Coolant. I have no coolant in the oil or oil in the coolant. I am not blowing steam out the exhaust. I have no coolant loss. I have no CEL. So I have eliminated a failed head gasket.

So I am down to two suspects, the water pump or the thermostat. I have eliminated the water pump because I am able to lower the coolant/engine tempature by running high heat in the cabin. My thought is I would not have water circulating through the heater core without an operating water pump. This leaves me the thermostat stuck in a closed position.

I apologize for the long verbiage. I just wanted to lay out the facts. I know this is a high mileage old car but for her entire life I have kept her perfect mechanically and cosmetically. I just want to find her ailment.

thank you!
 
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#2 ·
Your post was not too long, in fact it laid out the situation pretty well. A few questions: Did you have any physical indication that the engine was really overheating? This would be things such as gurgling in the coolant tank, or even overflow from high cooling system pressure. How about the electric fan; was it running at high speed? Was air blowing from the fan abnormally hot? Radiator hoses- top and bottom hoses hot or just warm? And do you have access to VAG-COM, as it would be useful to see what the second temp sensor in the coolant temp sensor assembly is reporting to the ECU. It's possible that your CTS, which is pretty new, is defective.
 
#3 ·
thanks for responding Yl, I did not hear any gurgling upon shutting the engine down. I did hear the aux fan running at high with the A/C off. I removed the CTS from the equation because I saw the temperature needle do the normal climb then descend when the cabin heater was turned to the high position. As I understand one side of CTS sends/tells the temperature guage what to do and the other side tells the ECU engine temperature condition.

The top radiator hose was warm/hot, I really do not know what would be normal. I could not check the bottom hose because I could not get to the hose with out removing my still intact belly sheild. With a failed thermostat should one hose be cool and the other hot?
Am I correct the engine hot water to the heater core will flow into the heater core via a by pass of the thermostat?
 
#4 ·
Correct, the heater core is not in the path of the thermostat, and if you've got a good supply of heat from the vents, the pump is likely OK. You should be feel both heater hoses being pretty hot, if the core is flowing coolant, and especially if the heater is not being used to blast heated air into the car. If the thermostat were to fail closed, then the radiator and both upper/lower radiator hoses would probably be fairly cool, since the coolant in them would be stagnant.

Regarding the CTS, you are correct that one of the sensor pair is for the "gauge', the other is for the ECU to compute fuel delivery. Using VAG-COM, you can check what the ECU's sensor reports, and compare that to what your gauge is showing. The gauge's sensor may not be correct.
 
#5 ·
thank you again Yl!
my first step should be to get the engine up to operating temp then see if upper and lower radiator hoses get hot. If they get hot then replace the CTS due to a sensor failure. If the hoses do not get hot then the thermostat has most likely failed in the closed position.

Are these the steps you would follow?
 
#7 ·
hi Tom, thank you for your help. My last timing belt change was in Feb 2010. Dealer replaced all associated components. I drive the car like an old lady, 80% is highway at 60MPH. The last I heard VW says change at 105,000. I plan on TB change at 260,000 in Nov of this year. This will mean 90,000 on this belt in less than 5 years. The previous belt and components showed little or no wear.

If replacing thermostat and or the CTS does not solve my issue then I will do TB and water pump. Living with this car for so long and she throws me a curve ball out of the blue is just driving me nuts.
 
#9 ·
Some non audi/vw sensors tend to have a different run temp load. I have done so specifically on my B5 S4 where the temp sensor kicks starts the pump at a much lower temp so when I turn off my car the pump still runs when the car is off so my turbos cool and not cook. Your cts may be defective if near to over heating.
 
#11 ·
While I would not rule out a sensor problem, it sounds more like the engine did get hot indeed. If you get good heat inside (especially with the car at idle) the pump is most likely good. At this point (assuming you had enough coolant and all the basics are covered) IMO the thermostat is the only possible culprit. But to replace the thermostat, you need to get to the timing belt, so plan a complete job anyway. TB kit, water pump, thermostat etc.
I would still replace the sensor first before it's a cheap way to start.
Just curious, did the car overheat when you were driving or idling?
 
#12 ·
Hi everyone, Following the advice given in this thread I will be doing the timing belt next week. Thank you all for steering me in the corect direction. I will also be replacing the cam and crank seals. I was able to contact the the mechanic who has serviced this car for the past ten years to do this job. He is retired. Could anyone direct me where I can get cam lock rental tools for this job? Thank you Guys!!
 
#13 ·
Blauparts has very complete TB kits, and also offers tool rentals. For your V6, the kit with coolant pump etc. is about $320, tool kit rental is $55. Their tool kit is a lot more than just cam and crank locks; it includes the sprocket puller and seal removal tools too.
 
#16 ·
You may also need to replace the thermostat plastic cover. They tend to break down right where it pushes against the seal, they it leaks when the thermostat is replaced.
 
#17 ·
thanks for the tip Pz. I will pick up a cover. My mechanic bailed on me, with phatcats TB instructions I will be doing this myself. I have a cam locking bar and the crank locking pin. I have done timing belts before on the Volvo 5 cylinder, but for some reason I have always been shy of this V6. I will also do the snub mount and valve cover gaskets while I have the car in service position.

thanks to all of you for your advice and help
 
#18 ·
Kahl
While phatcats TB instructions are very good step 48 where he states that he does not remove and re-set the cam sprockets is not the best way to go. You need to pop the sprockets loose to install the the timing belt correctly. There are specific puller made for this, but most people just use a 2 jaw gear puller. With the cam locking bar installed loosen the cam sprocket bolts about 4 turns and then use the puller to pop the sprockets loose. And they do Pop loose this is why it is better just to loosen the bolts and let them hold everything in place. i can post links to instructions showing this if you would like.
Here is a cheat sheet of torque specs I made up you may find helpful.

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#19 ·
Land vehicle Vehicle Car Volkswagen Motor vehicle
Hi Guys, I. Just replaced my timing belt!!!! Following Phatcats instructions and additional info from 2002GLXV6 it went on perfectly. Pz thank you for the heads up on the thermostat cover. The old timing belt was slightly stretched and in my humble opinion was ready to fail. I put the old thermostat in boiling water and it was frozen shut. The camshaft and crank seals were clean of oil so I did not touch them. Thanks for your advice Yl and Tom.

For what it is worth prior to doing this job I called the VW dealership to see what they recommend TB intervals, I was told 105,000 miles. Tom hit the nail on the head that TB should be changed before 80,000 miles.

Here is a picture of my now filthy Passat. She is 12 years old with 254,760 miles.

Thank you Guys for all of your help!!!!
 
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