Morris Minor Owners Club

Hi, I have been working on my Minor 1000 over the winter and took it out for a good run for the first time today, I noticed the temperature gauge which I have just fitted went up into the red, when I got back home I checked under the bonnet and noticed that all the hoses were hot apart from the bottom hose on the radiator also the radiator was hot at the top but cooler at the bottom, does this mean I have an airlock and if so how do I fix it.
Thanks, Bernard.

Maybe sediment settled at the bottom of the radiator?

When cold, remove the radiator cap and rev the engine, you should see slight movement of the water from right to left.

Were there any actual symptoms of overheating? It's normal for the bottom hose to be cold, especially in this weather, when all the others are hot.

You say you've just fitted the temperature gauge, so do you actually know it's reading correctly? Could it be a faulty gauge, rather than an issue with the cooling system? It's highly unlikely to be an airlock, I would say.

It is possible to develop an airlock if the system is re-filled with the heater valve closed ('cold' setting). With engine cold, set heater to hot. Remove rad cap. Start up and check for coolant movement as above. Coolant level may drop when thermostat opens and coolant flows into heater (check heater for heat output). Top-up if needed. Keep an eye on temp gauge. Until you're satisfied that there is adequate circulation, avoid running it in the red in case you damage the head gasket.

There are more reasons than yet stated, for a high temperature reading on a guage. Wrong value thermistor is one, wrong operating voltage is another. Wrong (or faulty) thermostat is yet another possibility.

First thing to do, as a start, is measure the temperature with a known reliable device, I would have thought. No point in chasing phantom faults.

If you haven't interfered with the water system recently, I think an air lock would be unlikely. If greatly overheating is the issue a clue would be the engine running on after the ignition is turned off. In which case, I would check thermostat as a start.

Thanks for the advice.
Bernard.