Mk1 Thermostat Temperatures

[Afndiesel]

My Mk1 tdi temp gauge gets to 3/4 then just stays there. Could it be the thermostat although new not opening enough. It doesn't go any higher and won't boil so I guess it's working to a point it's just disconcerting.

I recently changed the head, water pump and thermostat due to gasket going and this has happened ever since. Got annoyed and no matter what I do it won't boil. I just wonder if a cheap thermostat is faulty.

[BrianH]

It could be a dodgy sender - I've only got the petrol model to compare to, but there is two sensors on that, one that drives the gauge and another that is used by the ECU.

 

You can view the ECU one with torque on the petrol ones, might be able to do the same with VCDS to check how hot the coolant actually is?

 

Otherwise maybe consider changing the sensor? (I discovered this when the gauge sender for mine went faulty, and just read randomly anywhere between cold and boiling depending how it felt - checking the sensor in torque showed expected temperature of approx 80-95 degrees once it was warm and stayed there)