Losing coolant

[Martyn]

Went on 100km drive today. Coolant temp gauge initially just below 90 once warm, but dropped to 50 by end of trip. I probably lost up to 2 pints of coolant.

Will look for signs of leaks in week, but any ideas of cause of combination of low temp and low coolant?

Thanks in advance.

[GeorgeT]

Weak spring in the radiator cap may be the cause. Also, check your thermostat to see if it is stuck open.

[bobplyler]

Also, when the coolant is low, it doesn't reach the temperature sending unit, so it won't report the correct temp.

[fiatfactory]

.

[Martyn]

This makes sense. I have discovered a bead of coolant on water pump, but no staining on garage floor, which is odd, but maybe loss greatest when driving and coolant is under pressure.

No sign of gasket damage (yet?). Oil looks OK, no exhaust water. Will get pressure tests done and then consider next steps I think.

Thanks for all the help in diagnosing issue.

[Martyn]

This afternoon I discovered additional symptoms. The car heater doesn't work. The lever control only goes halfway but no heat at all.

After topping up coolant (about 1 litre) and bleeding the system the temperature gauge rose to ~ 60c after running the engine for 15 minutes. But the pipes to the heater were cool. Could an air blockage in this part of the system be a cause?