Temperature gauge fluctuating & heater not blowing cold.

[OldStoat]

I've owned an RX400h for a couple of years and still find it a real pleasure to be in.

Recently there has been some quirky behaviour from the cooling/heating systems, including the previously rock solid temperature gauge fluctuating between just below 'norm' and nearly into the red.

Eager to wick some heat from the engine I opened the windows and turned the heating up full - but the air was at most ambient. The gauge gradually returned to a more reasonable temperature again.

I think that a failing thermostat would be fairly binary in its affect - it would either work or not work, not work a bit sometimes. I don't think blockages in the heater core - because I know the car has been very well maintained.

There are some comments on the US site about air-flow servo - accessed via the glovebox (is that driver side for UK models?). 

Can anyone comment on the symptoms please - or advise about sensible course of action?

 

[CJJH]

Hello. First thing I would do is warm the engine up and touch the radiator in the middle to make sure it is hot. If it's the same temperature in the middle as the edges then the radiator is ok and not blocked. Then check the top radiator hose which should be hot also. This would indicate the thermostat is opening. Thermostats can fail in all manor of ways. Stick open or closed or not open all the way etc...

As for the stepper motors either side of the center console. You will have one that controls the vents on L/H side and one to control R/H side then one that changes cold to hot.

You can remove them and turn the bar manually to check vent function and also look at the motor wheel for smooth and full movement when you adjust controls on that particular side. (Plastic cogs).

I don't think it is these as you had strange temperature gauge readings.

I would change the thermostat and make sure ALL the air is bled from the cooling system. It's really important.

Hope this helps.