97 jetta td over heats only at higher speeds (over 100km/hr)

water pump impeller slipping?

That, or an old hose on the suction side collapsing under negative pressure. More common than you might think. Some hoses back in the day even had coiled springs inside to keep them from collapsing.

Peter Wieck Wyncote, PA

When driving on the highway and the temp. is high or hot : Try running the heater with the controls on the hottest / high setting as a test. Let us know the results.

I have changed the rad, thermostat, fan. The temp. is fine threw town, fan works good, no coolant leaks, it's full......Head gasket is new!!! I need help, I'm stumped!!!

Hoses? Did you read my post?

Peter Wieck Wyncote, PA

Was it the correct head gasket? How do you know? You compare the old gasket with the new gasket before you put it on. You compare water and oil passaged on the block and the head.

You did not mention replacing the thermoswitch. You do not mention running the bypass test of the thermoswitch.

You do not mention replacing the water pump.

Yes it was the correct head gasket.....Wouldn't the watter pump show other signs if it needed changing? ie: leaking, making noise....it's pumping when driving threw town aslwell...could you also expand on the thermoswitch, and bypass test please. thanks

Um... have you checked the hoses? Really, really, old hoses on the suction side will collapse under some conditions (usually at high speed), displaying exactly the symptoms you describe.

Peter Wieck Wyncote, PA

On my Rabbits there was a thermoswitch on the radiator. You remove the wiring plug and put a jumper wire on it. If the fan turns on it suggests the fuse and realy are good.

The plastic impeller could be slipping or maybe it slips more when the water gets hot. No signs of leaking as it is an internal problem. I do not recall any mention of mileage.

Note that you do need to make sure you check Peter's suggestions. Collapsing hoses are sort of hard to discover.