No heat coming from heater

[Gareth]

Hello all iam hoping you'll shed some light as iam pulling my hair out I bought a vw sharan 2.0tdi 2008.
Driving around all fine temperature goes up to 90c and stays there went on holiday I put the heater on a bit of warm air came out. Drove at 70mph for 5 mins heater went cold and car over heated. Its had a new waterpump done and the electric pump to. So I've changed the thermostat and unblocked the restrictor valve in the little pipe to the expansion bottle still no heat in car. I've tested the feed to the electric waterpump and it's dead no live feed I've checked all fuses does the feed come from a relay.
Any help would be great thanks

[johnnyroper]

I would say you have 2 faults going on. 

Electric water pump wonââ,¬â,,¢t cause lack of heat from cabin the engine pump should provide sufficient flow to the heater matrix. The electric pump is used to boost circulation to the rear heater. Not sure on the control side of things with the 2.0 would need a drawing to see whatââ,¬â,,¢s in the circuit and what controls it. I would assume thereââ,¬â,,¢s a relay involved.


The issue you describe sounds like head gasket related to me, does the cooling system over pressurise after a run?

[Gareth]

Hello no you can drive it all day below 70mph and it stays at 90c and even if stuck in traffic doesn't go above the temp. I was think of head gasket I had a vacuum test done to coolent no vacuum loss. No pressure In radiator in morning when cold.

[johnnyroper]

Thatââ,¬â,,¢s classic head gasket failure symptoms on a modern diesel, will run normally but push the speed up and it causes issues. Combustion gasses passing in to coolant ways causing air in cooling system and loss of heat and over temp. Whatââ,¬â,,¢s more traditional HG tests donââ,¬â,,¢t show up an issue as the leak only happens when engine is under load driven at speed.

[SirDavidAlhambra]

So much expertise here, amazing how you guys know all this stuff