icetrayz

Hey everyone,

Hoping someone has experienced this and has an answer for me. I havn't yet found any level of consistency on this issue, typically contradicting results.

In my '07 400h I am having heating issues. The heat will work just fine while the gas engine is running, I can turn it up high and the air gets hotter, turn it low and it gets cooler. Put it on auto and the fan speeds adjust normally.

What is happening is as soon as the gas engine shuts off the air goes cool and fairly quickly. This is most evident while stopped at a red light, as the gas engine just shuts right down. But it also occurs even at highway speed if i hit a section of road with a bit a down slope for a prolonged period. I can see on the screen the gas engine is shut off and sure enough the air gets cool.

On some sites people suggest the rad fluid top up trick. I have checked that and made sure levels are suitable. Some sources indicate these hybrids use an electric coil to create heat in the absence of the engine power, while others indicate the system actually switches over to an electric water pump to continue to circulate the hot coolant through the system.

I've had the vehicle into the Lexus dealership and they have not been able to diagnose the problem, however slapped me with a nice hefty bill to take a look. I still do not have clarity on how the system is supposed to produce heat in the absence of a running engine. Anyone able to provide that answer?

Has anyone experience this heat issue? I would assume it would be a similar system used on the other Toyota / Lexus lineup of hybrids? Any help would be greatly appreciated.

smassey321

The electric heater is a rumor but the electric pump mentioned is part of the system. With that said, unfortunately I have no idea where it is. I did see it was a $500 part.

Here is another clue for you. If you monitor your RPMs with a tachometer, you will see that your engine is not really shutting down while coasting at highway speed. It just slows the engine to an idle. Probably to keep the catalysts warm. If I had a heat issue, I would monitor coolant temperature with something like Torque for Android. This is the BT adapter I use. https://www.amazon.com/Veepeak-Bluet.../dp/B011NSX27A Your issue could be related to a bad thermostat. Unfortunately the thermostat is not super easy to change as it partially under the inverter.

icetrayz

Without diving into your suggestion, I think logic itself would indicate that it is unlikely a thermostat or coolant temperature. If at the flick of a gas pedal the air temperature is hot it can't be heating the coolant from cool to hot and then at a stop light the coolant goes from hot to cool. Additionally, as I mentioned originally, I can control the output temperature while the engine is running, so I don't think it is a thermostat issue on the air control system. The vehicle has a temperature gauge for the engine on the dash. and it acts as normal (starts low and gradually increases).

Ironically enough, since it is now winter here and -26 Celsius this morning, the vehicle operates very little amounts of time on electric only, so I haven't had to worry much about the heat issue, despite it being way below freezing. I'll have to diagnose this further in the spring I guess.