[Alexander Vitmer]

Constant loss of coolant in a 2002 Golf TDI, with 170000 miles. New radiator, thermostat and thermo-switch. Car heats up when driven aggressively, otherwise stays cool in traffic, as long there is enough coolant in it. Suspecting a cracked head gasket. No coolant in engine oil. Possibly engine pressure is pushing coolant out of overflow reservoir? Smell and micro-traces of oil in the reservoir. Any thoughts?

 

[pearlgolf]

It sounds like you found the problem. Try this: on a cold engine, open the reservoir and then close it. Start the engine and let it run, then open the reservoir again. Is it pressurized on the cold engine? If so, the pressure is coming from somewhere.

The EGR could also be leaking. This wouldnt explain the heat though.

When was the timing belt last done? If the water pump shaft separates it could cause overheting with no other apparent cause: http://www.myturbodiesel.com/forum/f5/always-replace-water-pump-cam-belt-4714/

 

[Keithuk]

Welcome to the forum Alexander. welcometomyturbodies

So at that mileage do you know the service history as it should have had 2 timing belts by now?

So your main problem is overheating rather than over pressurizing. Now I don't know what you spend on kit for your motors but you can get a CO2 detector kit that will analyse the gas in the expansion bottle to see if CO2 is present.

CO2 detector kit leak engine coolant

Save you buying a kit you could goto a garage and have them check it for you. I would say you could use an emmissions tester as that will test for CO2 but don't suck any fluid up with it.

The other thing is the water pump (it doesn't pump anything, bad name) working or has the impellor fell off?

As pearlgolf says just depressurise it and see how quick the pressure builds up again.

 

[pdq]

A quick test of waster pump impeller problems is to use the heater, if the impeller os stripped it will not circulate coolant and the heater will cool because of that. If there is good heat, there is good circulation, in which case I would suspect headgasket issues causing your overheat.