Odd overheating problem SOLVED

My '05 B5.5 started acting weird about a month ago. When towing a snowmobile, the temperature gauge start climbing but only on the highway. I would have to control it with the cabin heater. The funny part was that the needle dropped to normal when I hit a traffic jam or slowed to less than 80km/h. This only happened when I was towing the trailer with the sled on it. Last week when the weather started to warm up, the symptoms returned even without the trailer in tow. Again, all would be normal when I came off the highway and the speeds got lower. Saturday it started doing it even during city driving and I would just keep the gauve in control with heat. The more I thought about it the more the thermostat started to look like the problem. I figured it must only partially open so yesterday bought a new one with a new gasket and pulled it. I put the old one in a pot of boiling water and to my suprise, it didn't open AT ALL. Looks like these diesel engines generate so little heat that they don't need a radiator in the dead of winter. One the new thermostat went it and vented the heater core got vented, the temperature gauge went back to mormal.

That's why it's handy to keep a Scanguage II attached at all times. Then you see the temp readout.

The factory gauge showed the temp readout too so the only thing a Scangague would have done was to prove that the temperature sensor is working. The issue was either a clogged/blocked radiator, faulty thermostat, low coolant or too much air in the system.

imo000 said:

....The more I thought about it the more the thermostat started to look like the problem. I figured it must only partially open so yesterday bought a new one with a new gasket and pulled it. I put the old one in a pot of boiling water and to my suprise, it didn't open AT ALL. Looks like these diesel engines generate so little heat that they don't need a radiator in the dead of winter. One the new thermostat went it and vented the heater core got vented, the temperature gauge went back to mormal.

Click to expand...

Had the same issue. Was also surprised I could drive around with a stuck closed thermostat.

Thread of the original problem
http://forums.tdiclub.com/showthread.php?p=4497502#post4497502

Single Post of the thermostat issue in the same thread.
http://forums.tdiclub.com/showpost.php?p=4506875&postcount=25


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