I have an interesting problem on my VW Golf MK3 TDI.
Basically, sometimes the pressure cap on the coolant reservoir lets out some coolant.
Here's what I know:
- It happens when the car is under torque for a while (driving fully loaded on a motorway, or going up a small mountain).
- It doesn't happen when the car is not under torque (we drove about 1500km with light luggage, 2 people and a baby in the car, and no water was lost)
- The pressure is still there when the car has cooled down.
- There is no oil in the coolant
- There is no coolant in the oil.
- Thermostat works, I tested in a pan of water with a thermometer.
- Coolant reservoir (expansion tank) and cap are fine. I replaced them with new ones and the problem persisted
- The engine shows no signs of overheating. The thermostat remains at 90°C except of course if I idle the car for a while.
- The problem has remained the same for at least15000km
- The car is now at 227000km
- The water pump was replaced 2 years / 25000km ago
And here's what I think:
- It can't be the cylinder head gasket because of 4, 5, and 9.
- It can't be bubbles in the circuit because of 3.
- It can't be the reservoir or pressure cap because of 7.
- It can't be the thermostat because of 6, 8, and possibly 1, 2 and 3
I am at a complete loss at this point, as well as everybody I know.