Strange overheating problem.

temporarily stuck thermostat

Sorry, didn't concentrate enough on the info: Actually the heater stopping points to an air lock, so unless you have recently filled the system then the likely fault is either a leak which the header tank didn't refill (seen on Japanese stuff usually) or a blown head gasket.

In the absence of leaks get a header tank gas test done to rule out the head gasket if possible.

Never experienced it myself, but it certainly matches the symptoms. If I were the OP I'd cancel the pump order. and buy a thermostat. If it overheated again I'd fit it. Mike.

Which van? I've seen a loose water pump impeller behave like that.

I dont think it's the head, as the water level hasnt changed.

Suzuki Supercarry.

Thanks for the replies. Alan.

That has probably got the pressurised coolant system with an unpressurised header bottle (which is common on Jap vehicles, so it is possible to have low coolant in the engine but the bottle level stays the same. get the gas test done, no coolant change does not prove the head gasket is OK, I have changed head gaskets on those, also there is a tiny core plug under the cam that gets holed if the coolant is not regularly changed.

I've not seen a system where the thermostat regulates the coolant flow to the heater.

John

Saab 900 and 9000. 3 stage thermostat. Wouldn't cause the the symptoms described, but the third setting cut off the flow to the heater to avoid the passengers being burned if/when the engine overheated.