Coolant Thermostat: Buy Online & Save!

Hello.

Today I have a question regarding my coolant thermostat.

'Today I noticed that the upper radiator hose, which runs from the radiator to the cylinder head, was quite hot, while the lower radiator hose, also running from the radiator to the engine block, was relatively cool. According to the temperature gauge, the coolant should be normally warm, and the gauge was in the middle. However, the expansion tank was making a slight gurgling sound. The oil temperature was between 95-100°C according to the gauge.'

Is it normal for the lower hose to be this cold?

Or is the thermostat defective? I would like to test it to see if it's working, but it's not easy to quickly remove and reinstall. Maybe everything is actually okay.

The thermostat has been in use for approximately 6000 km. Today, the outside temperature at my location was 12°C or higher.

It's a Volkswagen Golf Mk3, diesel engine, 1.9L, with the AAZ engine code.

Thank you for your help, and best regards, Mark.

Hi Mark,

That is normal . You only need to worry if the coolant temperature is too high and the upper hose is cold, which means the thermostat is not opening . The hissing sound comes from the pressure valve in the screw cap of the expansion tank (which opens around 1 bar +/-).

Best regards, Christian.