Classic mini engine temperatures?

The engine temperature should mirror the thermostat rating temperature which can be found in the specifications page in the glove compartment manual.

Buy a $5.00 coolant/antifreeze hydrometer from any auto parts store to check the coolant freeze temperature ASAP. One quart of the incorrect antifreeze will not provide adequate freeze protection.

Certainly don't bother testing the thermostat, because all the symptoms point to it having jammed in the open position. One thing about the good old models like the Mini is that the parts are cheap. Last time I bought a thermostat it was about £3. Probably about £6 now. It looks like a small bed-spring with a rod in the middle and two brass ends. It lives under a domed housing next to the cylinder head, and one of your cooling hoses connects into that housing. You will also need a new gasket (they are paper, and pennies - buy a sheet of gasket paper and cut one of your own if they don't have one, and use some gasket paste with it). You will also need more antifreeze, as you will lose some when you open the system.

As said in another answer, buy a Haynes manual (try and get one secondhand if you can) as it will be worth its weight in gold to you.

Well done on checking the fan-belt and the coolant for antifreeze.

buy a haynes manual ( you will need it later for other jobs), and a thermostat and gasket,

follow the manual, job done

with a fault like this its often cheaper to replace the suspected part, rather than mess about with diagnostics and tools

i would also consider draining ALL the water and replacing with the correct mix ( if not a lil bit stronger) as you will partially drain the system anyway,

while your under the bonnet, check the rad itself for signs of corrosion and damaged fins, check all the clips are tight and no cracking to the ends of the rubber pipes

classic minis are great as they are simple to work on, parts are easy enough to get, just watch for skinned knuckles and rust

I would remove thermostat and simply get a gas stove, get a pan of cold water, dip thermostat in and heat it up. If it does not open or is already open but won't close then its broken and needs replaced.

You can get thermostats at any vehicle parts shop.

Edit

Remains open, keeps engine colder

Remains closed engine over heats

Sorry don't know where it is but a Heymans manual should

Take it and get the thermostat changed and get the anti freeze topped up to the correct strength.

This is classic 'Thermostat'.

Don't bother farting about 'testing it' in a pan of water !......Just replace it (or have someone do it for you). Job done !

One litre of antifreeze would not be enough