tdi 300

The coolant system in the disco tdi300 seems to be pressurizing.

Have changed thermostat as thought was gone due to getting hot,
It looks like the water is being pushed out from the thermostat housing back into the black bottle and when take the cap off water comes out and has pressure,

with the cap off I can undo the top screw on housing and after a couple of seconds the water returns into it and bottle goes back to normal Hight.

This will happened if disco is ran on drive for 10/15 mins.

Radiator will get warm,

No hot air in cab that can feel from Heaters.

Question is what could be causing this? Head gasket breaching to alow some gas into system?
water pump gone?

Sounds like an airlock in the heater matrix hoses.

does the water level alter at all when you rev the engine whilst watching in the expansion tank?

not looked, if leave cap off it over fills header tank. Even when just sat there on drive on idle.

would a blocked matrix cause it to pressurize?

Possibly water pump but does sound like HGF

big red 300 said:

The coolant system in the disco tdi300 seems to be pressurizing.

Question is what could be causing this? Head gasket breaching to alow some gas into system? water pump gone?

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It certainly a symptom of a head gasket failure, the water pump is just a circulation pump it won’t pressurise the system.
It could be an air lock in the system, but only if you have changed the coolant and it’s a result of not having refilled the system correctly.