Morris Minor Owners Club

Hi,
I just took my car on a ten minute journey and when I got back home, suddenly steam started pouring out of the bonnet. I opened it to find steam and water gushing out of the radiator cap, it had overheated. I waited for it to cool down then had a look at the plugs, they were white. The other day I set the mixture on the carb using the lifting pin technique. I seemed to be running rich so I leaned it out significantly until the lifting pin gave the right result. Judging by the white plugs, the fact that it overheated and the fact that I did lean out the mixture, I assume that I leaned it out too much and it caused the engine to overheat. Does this sound plausible? I really hope it hasn't caused the head gasket or anything else to go. I feel like I'm running on borrowed time with this engine but I'd really like it to keep going until I get the new one in as it's my only car.

So, is there anything I should be checking? Is it likely that it was just lean mixture? What is a reliable method for setting the mixture? The lifting pin technique didn't seem to work for me

It's highly unlikely that a weak mixture would cause that amount of overheating in 10 minutes.. Remember the 'pin lift' is only setting the idle mixture - the profile of the carb needle determines the running mixture, although the idle setting does have a slight effect over the whole range. As ever - check compressions... The Minor radiator is HUGE - in all my years, even with modified engines, I have never overheated a Minor ! Otherwise - could be blocked up radiator and/or block water passages - or (rarely) worn out water pump or even more rarely - jammed shut thermostat. If the compressions are ok - start looking at these other possibilities.

Okay, I'll check the compressions in a bit. I've only just replaced the thermostat and I checked the condition of the hoses recently so that seems unlikely. I also took it on a forty mile trip the other day and it didn't over heat

I've just done the compression test. Here are the results:

1: 130
2: 130
3: 115
4: 130

So, problem on 3?

They are all low - and #3 is poor - but nothing there to indicate gasket problems.

The engine burns a lot of oil and the compressions shoot up on a wet test. All I'm hoping for is that it doesn't completely pack up before I've finished reconditioning the new engine.

Indeed!

It just overheated again. Steam, boiling coolant. I have more clues this time though. Very hot heater, cold radiator, cold top hose. I'm thinking that it's a stuck thermostat or collapsed top hose although I've only just replaced the thermostat.

I've just managed to get it home and, of course, it overheated. This time the coolant didn't quite boil though. The water in the radiator was cool enough to put your finger in. I've checked the top hose and it's fine so I now strongly suspect the thermostat :/ That would be an easy job if the heater pipe wasn't in the way.

James k wrote:The water in the radiator was cool enough to put your finger in.

Suggest you use this method only when the car can reliably reach your local A &E..............

It does indeed seem like a rubbish thermostat. The water pump must be fine if the heater was working well!

I know this might sound a bit daft but is it possible you have fitted the thermostat in upside down, we all have senior moments occasionally

It's certainly possible that I put it in upside down! I can't see that being the problem though as I've done about 1000 miles since fitting it and it hasn't overheated. Now it's overheating every time. Is there any way of changing the thermostat without also doing the head gasket?

The thermostat is located under the aluminium domed cover at the front of the head held with three nuts. No need to disturb the head. When replacing the cover smear some copper grease on the threads of the studs and check the thermostat is placed with the spring at the bottom. You can test the thermostat by placing it in a saucepan of water and heat it up, it should open shortly before the water boils. Before putting the top hose back on the thermostat housing I always smear the outside of the housing stub with some gooey gasket paste (not the rubber type), it helps stop the white powder forming and gives a better seal if there is corrosion present.

I changed the thermostat a couple of months ago and greased the studs so it should be easy enough to get the housing off. The problem is that the heater pipe goes over the housing and is secured to the block under two of the head nuts. I don't know if I can just remove those two nuts without doing the head gasket

I'm not one hundred percent sure but I think you will find the nuts holding the heater pipe is the ones than hold the rocker cover and not the head itself but if I'm wrong there would be no harm in removing those two nuts to change the thermostat as long as you remember to tighten them back up when finished to the correct torque. To solve this problem in the future the next time you remove the head replace those two studs with ones a bit longer then torque the head down and place the heater pipe bracket over them then two more nuts on top. The next time you have to remove the heater pipe you will not disturb the head nuts.

It's definitely the head studs holding it down. That's what I'm planning to do on my new engine, longer studs and two bolts. For the moment though I'm not sure how to get to the thermostat.

I managed to bend the heater pipe bracket out the way and get to the thermostat. I've tested it and it works but I did have it in upside down. I can't see how this could be the problem though when it worked for ages before it started overheating.

I've now put the thermostat back in the right way round. I ran the car for significantly longer that it took to overheat before and it didn't. The heater was warm but not boiling and the top of the radiator got hot in the end. Hopefully that was the problem, fingers crossed!

Problem sorted then, well done. Put it down to a senior moment, we all suffer with it as time goes on