Morris Minor Owners Club

Hi all, my ‘52 MM sidevalve is over heating. Flushed radiator,all clear and water seems to flow through engine ok.Water pump is good,can see flow through radiator.The blades on the pump seem very small,is this correct? It’s been doing this for a few years now but not really a problem.Now bothering me to the extent that I want to stop it.Any help greatly appreciated,John.

A number of things could cause overheating:
Fan belt loose - although would expect battery charging problems as well, with the ignition warning light staying on.
Faulty thermostat - may not be operating at correct temperature or opening fully
Perished or collapsed/clogged radiator hose - check them all
Mixture too weak - although would expect some running issues
Valve clearances incorrectly adjusted - check them
Retarded ignition - again, would expect some running issues
I would suspect the thermostat first, unless there are other obvious running problems, in which case a good tune-up al round may sort it.
I assume it is the correct fan - someone with a MM model will be able to advise better on its size, although I doubt, like the others, that a large fan was fitted.

Over-heating? You don’t give any indication of symptoms. What makes you think it is too hot? Have you checked the actual running temperature with a reliable thermometer?

The fan may even be fitted back to front?

Mixture is good,,,,colourtune,,,,fan belt is tight,,,,no thermostat,,,,,temp gauge fitted ,ignition adjusted ok,reaches 120-140 and boils and steams through rad overflow,so that water does not enter through top hose to engine,new water jacket.It has always run hot but this year is worse.Tappets adjusted ok.Head gasket is new,no sealing problems or signs of water in oil etc.Sorry,should have included all this in original post.Whats the opinion of fitting electric fan between grill and rad?Although I would rather find and cure the problem.

Mixture is good,,,,colourtune,,,,fan belt is tight,,,,no thermostat,,,,,temp gauge fitted ,ignition adjusted ok,reaches 120-140 and boils and steams through rad overflow,so that water does not enter through top hose to engine,new water jacket.It has always run hot but this year is worse.Tappets adjusted ok.Head gasket is new,no sealing problems or signs of water in oil etc.Sorry,should have included all this in original post.Whats the opinion of fitting electric fan between grill and rad?Although I would rather find and cure the problem.

Just a point to consider:-
The water does not circulate from the top of the radiator to the engine but from the bottom of the radiator to the water pump and then through the head, then via top hose to the radiator and then down to the bottom of the radiator to circulate again.

Having a thermostat fitted pushes the water to the back of the block which helps to keep the block cool.

Have you flushed the cooling system - is water getting from to and from the bottom of the radiator to the water pump in sufficient quantity to be of use?
I would check that the radiator and bottom hose which feeds the water pump is not blocked or obstructed with sediment.
Undo the coolant drain and see if there is water or sediment coming out or nothing at all.
Give the engine a good flush out and see what happens and if there is any improvement. Use a engine coolant flushing compound if necessary.

Thats interesting Phil.I will fit a thermostat back in and try that.

I would recommend that you flush the radiator and cooling system as a matter of course and check the bottom hose for sediment - fitting the thermostat will/may only go part way to curing the problem.

Thats interesting Phil.I will fit the thermostat back in and try it.All engine and hoses and rad are completely clear.
Thanks all for your input.

When I rebuilt my engine many years ago I found a huge amount of silt/debris in the block, even found a nail! - presumably from the casting process.
Might need a good poke with wires and rods.

Alan

I know you say you have flushed the rad and it and the engine block are clear, but it may be worth reverse flushing while you are fitting a thermostat. Also, do check (as Oliver90 suggests) that the fan is on the right way round. Does it overheat at speed, or only when moving slowly/idling?

iirr if you remove the thermostat you have to fit something in its place otherwise the water only circulates round the front of the engine and does not reach the back and so causes over heating. I think it is some sort of baffle that you fit in place.

amgrave
This is the baffle plate you are most likely referring too.

http://www.minispares.com/product/Class ... thermostat .aspx|Back to search

If the thermostat is removed from a 803cc to 1275cc OHV engine it is an absolute must that it is fitted to divert coolant to the rear of the block unless other means of pushing coolant to the rear of the block is incorporated.

Only overheats at speed,fine when moving slow or idling.

Check the radiator fins are not blocked and thereby restricting air flow.