On a much older car, I used to start it with the cap off, heater on max and rev the engine for 10-15 minutes to try to clear any air. Depending on what set-up it is, you can probably give the hoses a squeeze whilst it's running, cap still off, and get the occasional satisfying belch out of it.

Dunno if these are especially problematic for airlocks, but on the Skywing, which seems to be, I jam a series of funnels, champagne-glass cascade stylee in the radiator fill port, to provide expansion room, then I run the engine with the cooling fan disabled until the coolant boils, clearing the air.

A bit alarming, but I feel its safer than running with an air pocket in the system.

The user manual advises to stop the car immediately if the warning light flickers.

Generally speaking, is it safe to run a car when the fan is operative? In the past, I have been stuck in traffic queues when the fan comes on. But not in open traffic as far as I can recall.

Kind of an odd question. The fan comes on when the coolant temperature at the sensor location is higher than a preset. It would be unsafe to run a car when that was the case and the fan was inoperative, because there would be a risk of overheating damage.

In open traffic your forward motion probably induces sufficient airflow in normal circumstances to keep the temperature below that at which the fan would come on.

If this has changed, it suggests either your system isn't cooling so well as it used to, the temperature sensor and/or the control gear, including the ECU, is commanding the fan on incorrectly, or (less likely) the engine is generating more heat.

On old style cars you can bench test the operation of the temp sensor and thermostat using hot water. Dunno about newer ECU-controlled systems.

Heating/cooling many possibilities...clogged radiator (inside or outside), defective thermostat, water pump failure, air pocket, brakes binding, bearing failure, low oil, running lean, engine mistiming, er...head gasket failure. The last is something of a worst case cooling-wise and is not specifically indicated by your symptoms as reported.

At the moment my temp sensor is disconnected and I switch the fan on manually when I drive the car. Doesn't do any harm apart from fan wear and excess electrical demand.

Edited by edlithgow on 13/07/2022 at 11:49