I bought my 83 300D from Turbodiesel approx. 1 year ago.

To date, its been a great car with a few minor cooling system problems.

Around december of last year, it had a mysterious coolant loss problem, whuch disappeared just as soon as it showed up. An oil analysis revealed no coolant in the oil, and a coolant analysis revealed no hydrocarbons in the coolant. Head gasket? nope.

Just yesterday, about one block from my house the temp gauge climbed to 120C and held there. gotta be the gauge, so I shut it down and jump out. Top coolant hose is cool, but under enourmous pressure. I can hear coolant boiling in the engine. Engine is extremely hot.

So I remove the thermostat and test it. Its fine, its stamped 176C and was opened almost fully by 190C. Several tests of the thermostat revealed it was operating just fine. So I removed the water pump. It wasnt leaking and it also appears to be in great shape. its kinda jerky when you turn it, but nothing that would alarm me. the fan belts and fan clutch were operating fine and werent loose.


I cannot figure out what the heck is wrong. thermostat is fine, water pump APPEARS to be fine, new radiator, nothing else wrong, just random overheating. any ideas?

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Matt
2003 Jetta Wagon TDI 145,000MI
1999.5 Jetta TDI 287,000MI
2001 Suzuki SV650S 26,000MI
2008 Yamaha Vino 125 11,000MI
http://www.crazymatt.org