Morris Minor Owners Club

myoldjalopy wrote: ↑Wed May 21, 2025 9:12 am "Already somebody has had the first overheat problem. This often seems to happen on the way to the ferry."
If this is the case, I wonder how often these cars are used during the rest of the year? Of course, things can go wrong at any time but this seems more than coincidental. When I was a boy, a Morris Minor driving great-aunt impressed upon me how the cars need regular usage, a bit like exercise

I think that's true. Many cars just bimble about the local village or town most of the time. It isn't until they are a bit more stressed, loaded with luggage and people or stuck in a traffic jam that they have a hissy fit. Last year there was a breakdown in a puddle of oil yards from the owner's house!

As for coincidence, well I take the point but over the last 2 weeks I have had: leaking heater valve (replaced); leaking timing chain cover (fixings tightened, fixed) and a starter motor that would not engage (dirty Bendix, fixed)........All of these could have happened in France or on the way there.

Stephen

Yes, as I said, anything can go wrong at any time but let us hope that your gremlins have been vanquished and that all goes well in France now - good luck!

myoldjalopy wrote: ↑Wed May 21, 2025 11:07 am Yes, as I said, anything can go wrong at any time but let us hope that your gremlins have been vanquished and that all goes well in France now - good luck!

Thank you very much and hoping the OP sorts his issue or at least allays his concerns with a thermometer.

Stephen

myoldjalopy wrote: ↑Wed May 21, 2025 11:07 am Yes, as I said, anything can go wrong at any time

Many months ago I managed to replace the oils in my car, but then ill health prevented me working on it.

Roll on 10 months and I risked moving (pushing) the car, only for all the diff oil to be found on the ground after I'd moved it.

The fact it had been dry under the car for ages after doing the oil changes, makes me wonder why it suddenly decided to unscrew enough to start leaking, so yes "wrong at any time" rings true.

I’m going use my van soon, after a long period of inactivity ——- what’s going to go wrong ?

Hello everyone finally got around to looking at Molly again, I got her good and hot and tried taking various temperatures with new thermometer as suggested, readings as follows,do these sound reasonable, top hose 89c, bottom hose 77c, top of radiator 104c, water in radiator 92c, hose into heater 84c, hose out 77c, air coming from heater 52c, thermostat housing 87c. I closed heater valve and then noticed water coming out of radiator overflow hose and a little around top of cap so slowly released cap, quite a lot of pressure, still need to check timing as soon as I get some time.

What radiator cap do you have fitted?

I'm a bit puzzled by the figures because the top of the radiator cannot be hotter than the top hose. They must be the same temperature or the top of the radiator very slightly less than the top hose. 104 C for the top of the radiator is a hot but 89 C for top hose seems entirely normal to me......

If the radiator is overfilled then the cap will vent to the overflow pipe. The radiator is only filled until the coolant is just above the core pipes inside the radiator but if overfilled it will overflow and find the correct level.

Stephen

I'm with Stephen on this, the top of the Radiator should be similar to the top hose/thermostat housing....
89C is about right for the Thermostat being open.
I've been regularly checking mine, simply to check the calibration of the Temp Gauge I fitted.
I'll be checking it some more this weekend as I've just fitted a new Rad Cap, having realised the old one just wasn't holding any pressure.
With the engine hot I could compress the top hose and when released, I could hear air get back in past the cap, giving a little wheeze/whistle noise.

Incidentally, was a standard 82 C thermostat fitted? I know the OP said it was an 82 but they are marked on the thermostat. There is also an 88 C which is usually only used for winter use when the engine has difficulty getting up to temperature (it also gives a hotter heater sooner). The 88 C thermostat is too hot for warm summer use. ESM sell both 82 and 88.

Funnily enough, before the Minors on Tour trip I noticed that my radiator cap (4 Lbs) was not making a proper seal and I replaced it.

I've never really bothered to think about radiator caps. Presumably a cap marked "4 lbs" is 4 PSI ABOVE atmospheric pressure which is 14.7 PSI. That gives 18.7 PSI at which water boils at approximately 106 Centigrade.

So if the top of the radiator really is 104 C it is rather close to boiling. Too close I think. But if it is actually 89 C as the top hose temperature is reported that's fine......

By the way, a properly functioning heater IS rather hot. It's quite a powerful little heater. Powerful enough that I drive my convertible top down in the winter with the heater on and get a useful blast of heat.

Stephen

Maybe the op is measuring the top of the radiator that's not in contact with coolant so gives a higher reading. There can also be a variance in reading due to the reflectivity of the surface when using a temp gun.

Water boils at 212°F (100°C) at sea level. 

Coolant and antifreeze:

A 50/50 mix of coolant and antifreeze has a boiling point of 223°F (106°C) at sea level pressure. 

Pressure and boiling point:

Each pound of pressure raises the boiling point of the coolant mixture by approximately 3 degrees Fahrenheit. (1.67 C)

4lb cap:

A 4lb radiator cap will raise the boiling point of a 50/50 coolant mixture to approximately 236°F (113°C). 

Bill_qaz wrote: ↑Sat Jun 07, 2025 12:01 pm Maybe the op is measuring the top of the radiator that's not in contact with coolant so gives a higher reading. There can also be a variance in reading due to the reflectivity of the surface when using a temp gun.

Water boils at 212°F (100°C) at sea level. 

Coolant and antifreeze:

A 50/50 mix of coolant and antifreeze has a boiling point of 223°F (106°C) at sea level pressure. 

Pressure and boiling point:

Each pound of pressure raises the boiling point of the coolant mixture by approximately 3 degrees Fahrenheit. (1.67 C)

4lb cap:

A 4lb radiator cap will raise the boiling point of a 50/50 coolant mixture to approximately 236°F (113°C). 

Ah I forgot the antifreeze raising the boiling point....

When I get a chance I will take some readings on my car.

In answer to the high temperature at the top of the radiator, yes the temperature was taken above the waterline on the outside too of the tank. The cap is a 4lb cap and the new thermostat came from ESM and is marked at 82 degrees.

In my opinion assuming your running a water antifreeze mix or ready mixed coolant then it all seems fine. As stated previously don't overfill the radiator and check daily when cold during use so you know you are not losing water. If you are concerned then fit a temperature gauge for peace of mind. Drive it and enjoy.

Above, Svenedin states "The 88 C thermostat is too hot for warm summer use".

May I say that I've successfully used 88C thermostats (and even one of 91C) for all seasons over some years. Currently I've been using for a few years a 85C thermostat and will in due course raise it back to the 88C item. I've no trouble on my 1098 Trav even when driven hard for long spells (i.e. 60-65mph true) in hot weather.

Regards from MikeN.
PS As a digression, a higher coolant temp needs a smaller radiator to lose the heat (Newton's Law of Cooling shows that heat loss is proportional to the temperature difference) and this point was particularly important in WW2 liquid cooled aero engines. By 1942 the Merlin coolant was running at 125C while German engines were at 115C which allowed the Merlin radiator to the just over half the size of the German requirement with the commensurate reduced air drag penalty. The German discussion of this topic is at page 296 of "The Secret Horsepower Race - western front fighter engine development" a book which I thoroughly recommend.

Jonessa wrote: ↑Fri Jun 06, 2025 3:33 pm do these sound reasonable, top hose 89c, bottom hose 77c, top of radiator 104c, water in radiator 92c, hose into heater 84c, hose out 77c, air coming from heater 52c, thermostat housing 87c.

All except the Top of Radiator being 104C, when the water is 92C.....
The metal not in contact with the water 10% hotter than the water that's providing the heat...
That just doesn't make sense.... unless you had achieved such a high temperature and then stopped the car, left it running and opened the bonnet to check the temps. If the water was still circulating, it would rapidly cool down the whole cooling system, leaving the un-wetted metalwork to rely on just ambient air to cool it.
But then how did you open the radiator cap to check the 'water in radiator'...
Or are you saying all measurements were taken with the Radiator Cap in place and these are temperatures of the external metalwork at various locations...

This small anomaly aside, there seems to be nothing wrong with your findings, so stop worrying.