erratic temperatures...or erratic guage?

[Sundancer]

Pulling my hair out trying to diagnose an issue which seems to defy logic....


Temp gauge swings rapidly from 12 o clock to one bar before red...and back to 11 o clock, no heat at defrost,

Thought maybe thermostat, but if so it is opening and closing at will, not stuck,
thought fan, but it goes up and down whether at highway speeds or not...

thinking temperature switch? Is there any correlation with the gauge, and the valve that cycles to provide flow for the interior heat? I don't hear the usual clicking from the flow valve for lack of a better term, so maybe its not opening? could this somehow manifest itself as the swinging gauge?

[Timm]

If you have no cabin heat you are probably short of coolant - parts the cabin heater (such as the pipework) is the highest point of the cooling system so usually suffers first. The cabin heater is not affected by the thermostat (unless the complete system fails to reach temperature) and is in a separate loop.

All explained here:

[Sundancer]

You were correct...I put the front end up about 50cm, it took almost two litres of coolant, appears to be operating normally now...thx

[TedBobo]

You were correct...I put the front end up about 50cm, it took almost two litres of coolant, appears to be operating normally now...thx

Where'd the missing coolant go?

[Sundancer]

That...

is a very good question...

Investigation to follow....