Rover V8 overheating - Expansion tank dry

[Chuck21]

Hi folks. My buddy has a Cobra rep on a Rover V8. It overheated on a drive, no issues driving but water temp through the roof. Took a look and no obvious leak but expansion tank dry. Is most obvious issue a minor leak from a hose or similar that wasn’t noticeable as it would just evaporate in/from the engine bay?

Any advice welcome, thinking we just fill up from the header tank, start her up and watch for leaks?

[Wanchaiwarrior]

Have you checked the oil, to see if the coolant has mixed with the oil ?

[Chuck21]

Yeah, oil is all clear.

We drained it from the rad bottom hose (not a lot came out) and re-filled then ran it for a good while. There was the odd spike but overall it stayed in range. As you say I think the next step is to fully pressure test to make sure there aren't any other issues.

[sospan]

Is the pressure cap ok?
After the refill are you sure the system is fully cleared of air/airlocks?
What antifreeze is in it? Mixing types can cause blockages.
Is the water pump ok?
I have a later Rover V8 in a Morgan . Gems management not carb. It is sensitive to airflow through the rad but the fan kicks in.
How is the airflow through your mate’s rad and is the fan ok? Check the temp sensor switch that controls it. In older Rover V8’s this is an Otter switch that is known to pop out.

[jhonn]

It's likely to be a head gasket that's gone; the Rover V8's are prone to this. When running, the engine pressurises the cooling system through the leaky head gasket and pumps the coolant out of the expansion tank.

There are three rows of bolts bolting the head to the block - it's the outboard row that 'cantilever' the head and eventually cause the gasket to fail.

When it happened on my V8 LR 90 I replaced the gaskets and didn't install the outboard row; I never had any issues after that.