Rx 400 thermostat change

JSeaman · August 31, 2020

Has anyone changed the stat on an rx400 and if so did you need to remove all the hybrid system?

ColinBarber · August 31, 2020

It's a major pain. Wipers and motor all out to remove the top cowling, drain engine and hybrid coolant, disconnect/remove the power steering ECU, remove air box/filter - and yes the hybrid inverter needs to be removed.

I think you want to be sure the thermostat is faulty before doing this, not just replace it on a whim.

JSeaman · August 31, 2020

Wow that sucks, I have the fans kicking in, no heat in the cabin, one cold hose and one hot one so I figure it's the stat

Is there a decent service manual around anywhere do you know?

Herbie · August 31, 2020

Just PM'd you with some info that may help James.

JSeaman · August 31, 2020

That is hugely helpful, thank you so much for that! I'll give it a try and see how I fair, many thanks

welland · August 31, 2020

12 hours ago, JSeaman said:

Has anyone changed the stat on an rx400 and if so did you need to remove all the hybrid system?

Is there a single thermostat, or two: one for each coolant circuit?

ColinBarber · August 31, 2020

16 minutes ago, welland said:

Is there a single thermostat, or two: one for each coolant circuit?

Single. The hybrid cooling system has a separate pump and uses a separate core within the same radiator assembly but there is no need for a thermostat to regulate an optimum temperature as with the internal combustion engine - the colder the better to keep the electronics and motors cool.

JSeaman · September 13, 2020

Well, the stat is changed - not too bad a job after all, only took an hour to strip it all down.

I tested the stat and it opened but slowly and slightly so wanted replacing but wasn't enough to cause the symptoms. Moved over to the other side of the engine and the water pump is weeping so that's now being done along with the timing belt. Thanks again to Herbie for making this a lot easier than it would have been!

Herbie · September 13, 2020

You're welcome James, glad I could help.

JSeaman · September 19, 2020

Well, things were going well but hit a bit of an obstacle. The timing belt and and the water pump are done but it says Check Hybrid System and Check VSC System when I try and start it. I've put a charger on the 12V cell in the engine bay but it's reading 12.3V so don't think it's too low

Brandipity · August 20, 2022

On 8/31/2020 at 9:17 AM, Herbie said:

Just PM'd you with some info that may help James.

Hi Herbie, the thermostat on my wife’s 06 400H has decided to stick open, and I’m looking to replace it. Would you mind relaying this info to me as well? Thing looks like an absolute nightmare to replace.

Herbie · August 20, 2022

8 hours ago, Brandipity said:

Hi Herbie, the thermostat on my wife’s 06 400H has decided to stick open, and I’m looking to replace it. Would you mind relaying this info to me as well? Thing looks like an absolute nightmare to replace.

Hi Brandon,

Just sent you a PM which will hopefully help.

Burtwyn · October 20, 2023

Hi all,

I know this is an old post, but my mechanic thinks my thermostat has failed too. I've had a cracked radiator and the car is still overheating after replacement. The bottom radiator pipe is remaining cold leading him to think the thermostat has gone. @Herbie would you be able to share the details on replacement with me too please. TIA :-)

Herbie · October 20, 2023

2 hours ago, Burtwyn said:

Hi all,

I know this is an old post, but my mechanic thinks my thermostat has failed too. I've had a cracked radiator and the car is still overheating after replacement. The bottom radiator pipe is remaining cold leading him to think the thermostat has gone. @Herbie would you be able to share the details on replacement with me too please. TIA 🙂

Just sent you a PM now Roger, hope it helps.

htyler · May 20

Hi Herbie. I know this is an old topic but I'm researching best method to replace the thermostat in my RX400H. Local garages do not want to touch it. Could you send me the info you have shared with others please. Many thanks

Kev.S · November 14

Hi Herbie, same request please: the thermostat on my 06 400H has decided to stick closed, and I’m looking to replace it. Would you mind relaying this info to me as well? Top hose is warm, bottom cold and no heat in cabin.. Really appreciate your help, not looking fwd to this job at all!

many thanks