Overheating

[Vic Butler]

I'm reviving this topic because today a mate suggested that the overheating could be due to the bottom hose collapsing. The hoses are Kevlar.
I can't quite see how it could be the cause as overheating occurs as soon as the throttle is applied and the engine has to pull a bit harder. I would have thought that if the hose collapsed the overheating wouldn't be immediate..
Despite there being no water loss I still think that somehow the cooling system is being pressurised and even if I slow down and drive slowly on a very light throttle the engine doesn't cool down.
Any ideas? It's not sticking brakes as I can push the car easily.

[Paul Scott]

Did you check the water pump Vic?

If the impellor has shrunk it may not be able to circulate the water quick enough once driving. Is the heater blowing hot air, if cold this could be another sign of the pump being an issue.

I'm no expert.

Paul

[Vic Butler]

I eliminated the water pump because when I run the engine at about 2,000 rpm in the garage it behaves normally. It's only when it has to pull that the temperature immediately shoots up.
I have removed the manifolds (much easier with brass barrel nuts) but it's too cold at present to get in the garage to remove the head.

[Ian F]

Hi Vic. I think I may have said this before, but I suspect overheating under load could be either;

1. Timing not correct - igniting fuel at the wrong point of the cycle will cause overheating. Timing may
be correct at idle but way off when under load at higher revs.

2. Possibly a too weak a mixture under load. Too much oxygen equals too much heat! Less likely than 1., but possible.

Ian F.

[Vic Butler]

The strange thing is Ian that as soon as the engine starts to pull even up a gentle incline the overheating is immediate. Only a few bolts left now and I can remove the head. I suspect a crack because it had to be modified to take MGC inlet valves because one of the combustion chambers was damaged around the valve seat through ingesting something. It wasn't the original head, I got it from a mate. It was free and it was the big valve head.

[Ian F]

Well Vic, hope it's not a cracked head, good luck with getting it sorted out.
Best wishes for the festive season!
Ian F

[Vic Butler]

Thanks Ian. Merry Christmas and a Happy New Year.

[Statler]

I assume that you've checked the overflow tank?
Our Midget 1500 was repeatedly overheating and spitting water out of the overflow tank cap.

We replaced the cap, checked hoses, new water pump and just about everything else suggested. We even changed the head gasket just in case, but none of that fixed it.

The problem was the siphon tube in the overflow tank, or lack of... it had corroded and so the hot coolant was getting pushed into the tank but not being sucked back into the cooling system. Each time there was too much coolant, it overflowed via the pressure relief in the cap and then there was too little coolant, so it got very hot.

A new to us tank with a siphon tube solved the problem.

[Vic Butler]

It's very strange but there's no water loss whatsoever. I've removed the manifolds.and it's just removing the head. I did a compression test and number 4 is down on the others but by only 5psi well within the tolerance but that's where I 'll check first.
In the Land Rover world Elring head gaskets are recommended. Are they available for MGB's does anyone know?

[Statler]

In the MG world PAYEN head gaskets seem to be 'de rigeur' but I couldn't get one when rebuilding the B last year.
They seem to be more readily available now : https://mgbhive.co.uk/product/11-geg116 ... asket-set/

I just used a normal copper gasket and it's holding up ok.