Overheating - Whats left?

[BrynWyn]

Hey!
So I have a overheating issue with my 1990 Rev1 Tubby.
The water pump on my car started p1$$ing out so I fitted a new water pump, its stopped leaking but still randomly gets hot now and again.
I fitted a new upgraded aluminium radiator and it was fine for a while then it got a lot worse, so I tried a new thermostat and it was the same. I removed it and it was fine again for a little while then started randomly getting hot again.
I have also fitted a new temp switch but its still the same.
To compensate for all of this I fitted twin cooling fans on the underside of the engine lid, and put the inter-cooler and radiator fans on constant, but still hasn't done much.
I compression tested the engine and it came up with 160psi on each cylinder and there are no signs of head gasket failure.

The only other things it could be that I can think of that I haven't tried yet are the radiator cap (mine isn't in the best condition, so I've ordered a new one).

The heaters in the car don't really blow hot air so that might be connected to the over heating issue.

Any ideas?

Thanks in advance

EDIT:
It doesn't overheat at any particular time. Can be cruising on the motorway doing a steady speed, and then suddenly the temp will shoot up. The same can be said when you are cruising along a 30. If you notice the temp raising, and put your foot down it will normally drop the temp gauge for a bit.

[SonicSW20]

Have you bled the system? Sounds like you've got an airlock.

[craig]

When was the coolant last flushed and refilled with all new coolant? Sounds like it could be a blocked hose somewhere. Old coolant leaves a crusty brown lining on the hoses which can build up, leaving the hoses feeling crunchy when squeezed.

Just a thought anyway.

[Mullen]

Have you bled the system? Sounds like you've got an airlock.

Certainly does.

@OP Follow this guide, ignoring the rad swap bit... www.mr2oc.co.uk/know-your-2-knowledge-b ... bartid=161

[bobhatton]

When it overheats have you lost water?

If so have you checked the heater pipes above the fuel tank, that are a problem and not easy to see when thay leak

[BrynWyn]

Have you bled the system? Sounds like you've got an airlock.

Yes it was bled properly following the guide that Mullen posted.

When was the coolant last flushed and refilled with all new coolant? Sounds like it could be a blocked hose somewhere. Old coolant leaves a crusty brown lining on the hoses which can build up, leaving the hoses feeling crunchy when squeezed.

Just a thought anyway.

Coolant was flushed two weeks ago, and two months ago.

When it overheats have you lost water?

If so have you checked the heater pipes above the fuel tank, that are a problem and not easy to see when thay leak

Nothing has been lost

Any other ideas?

[tiff_lee]

So was the car overheating before you changed the waterpump?
" its stopped leaking but still randomly gets hot now and again. "

So when running without the thermostat it was still overheating randomly?
" so I tried a new thermostat and it was the same. I removed it and it was fine again for a little while then started randomly getting hot again. "

Overheating without a thermostat and no hot air in the car, airlock or coolant flow problem.