Hi all,

Maybe someone seen this issue before and knows the root... When car driven for a while, i notice that when running on battery power like in traffic or at red light, my heat stops producing hot air... When gas engine kicks in, everything is back to normal.

TIA

 

I think there is an electric coolant pump that keeps the hot coolant circulating to the heater core when the gas engine is off. You may want to check it.

 

Pump is belt driven all the way through 2018 models. I even posted picture of 2018 V6 hybrid engine with clearly showing belt. It's auxiliary belt, one and only on hybrids. New Camry Hybrids have electric pump.

heat is not produced because:
1. pump is not spun
2. engine does not operate. Engine is the only heat producer. Camry Hybrid has PTC heater.
I'd not say mine does not produce heat at all, but when I mostly in EV mode, heat falls down and changes to lukewarm. Watch temp gauge. What does it show? Mine will drop down to almost nothing, as it's cold outside.

 

RX400h coolant is pumped with a timing belt driven pump and an additional electric water pump.

https://www.lexussouthatlantaparts.c...720048020.html

The engine temp gauge is measuring coolant temperature in the block. If it goes down at the same rate as the level of heat, the electric pump is working.

 

Ukrkoz, I believe you are wrong. The RX400h has 1 belt, and it is the timing belt. Yes, the main engine water pump runs off of the timing belt as well, but it is not visible at all, as there are protective plastic shrouds hiding it from view (even if you pull all the plastic engine covers off first). The Rx400h also has an electric auxiliary water pump that pumps heated coolant through the heater core when the engine is not running. As smassey321 has suggested, I would ensure that it is functional. There is probably a way to activate it using Techstream...

 

Engine is not running there is no heat produced. Pump it all you want to, does not make it any warmer. They should have done same set up as on Camry Hybrid - install PTC heater before heater core, so ICE running or not - coolant in core is hot. That is one thing I really miss from my TCH.
I also keep forgetting that older V6 hybrids had belt, not chain. My 2012 3.5L hybrid has auxiliary belt just for the pump.
Here's 2GR-FXE for RX450H


2GR-FSE



And 2GR FXS used on late RX Hybrids


They all appear to have a water pump belt.
I mean, I get it - there is additional mini pump to circulate coolant. But if engine does not run, what is producing heat?

 

It looks like when they switched from a timing belt to a chain they didn't have anything to drive the water pump anymore, so they put it on it's own little belt. Cool. I didn't know that. I also just assumed they put PTC heaters in like the Prius, but after searching I find no sign of it being in the Rx400h. I guess the V6 warms up a little quicker, so they didn't need it.

 

Thank you all for chiming in.

The actual solution was much easier and cheaper than expected Adding about 1/3 of a gallon of coolant to the system solved the issue for me. I can't believe I didn't think of checking radiator level first... Duh