RX400h Auxiliary Water Pump Issue

[Ridgeback]

Has anyone had similar experiences?

As long as the engine is running (not idling), the heater works, but if stationary or deaccelerating the heater blows cold as the auxiliary water pump is not doing its job

Thanks in advance

[Herbie]

Could be an airlock or low coolant level.

[Greisingel]

Had same experience. Herbie is almost certainly right. Drain and refill, engine running (with heater, lights, the works on). Use a filling chamber on neck of filler to make sure every last air lock is removed.

[Ridgeback]

Thanks for your advice