Lexus GS 450h 2010 Face Lift Transmission Fluid

ayrtonsenna · May 14, 2022

Hi every Lexus lovers 🙂

I want to say very big greetings for everyone who take their own time and experience to maintain our Lexus and share their experience on our forum.

Today I spent all day to find a possible way how to fill in a transmission fluid to GS 450h e-CVT transmission. My Lexus reach 110 000 miles and I thought that will be a kind of obvious of maintanance.

It seems like it is not possible. Many of YouTubers, a lot of of forum's says that you wiil need a few tools and some experience. OK... that's all true, but not for my Lexus. My "gearbox" is a e-CVT transmission, which looks like a Lexus improved model, really do not need a transmission fluid change or refill. I attache a photo, maybe not very good quality, but real photo from the face-lift model.

Everything looks good, we have got drain plug, we have got a level plug... but where is a filling plug? Just not exist. Only one possible place, marked on the photo. Can anyone confirm? Very difficult acces... not surprissingly wrong according to no-maintanance gearbox, on the top looks like for allen key ( again ... can anyone confirm a size of tha allen key? looks like 6). Honestly I think to make a serious service with the transmission, I'm going to remove the oil pan, change the gasket and filter, fill in a new fluid. But WHERE IS THE FILLING PLUG?
Another question is... what type of fluid works in the e-CVT transmission? According to any information found on the websites it is a ATF WS... but none of those websites is for 450h, hybrid version.
So... I'm confused still, I have a lot of electro-mechanical skills and experience in maintanance, but Lexus never going to stop surprising me 🙂

Mihanicos · May 15, 2022

There is no filler plug, you have to disconnect the top rubber hose to the oil cooler on the driver's side. ( There are two, flow and return.) Plug the rubber tube to the oil cooler and add about half a litre more oil than the amount you drained. You drain about 3.5 litres.

Make sure the car is levelled on stands. After you add oil, reinstall the rubber hose and go through each gear twice, remaining for 5 seconds in each one. It is important to circulate the fluid so you do not line pressure TDC.

Keep the engine running and observe the transmission fluid temperature. You can read it from a scanner or using an infrared laser thermometer.

You drain the excess oil between 30C and 40C. For uk i would drain at 35C.

Go for a test drive and make sure you have no line pressure DTC. If you have, add half a litre of fluid and repeat the process.

Use Toyota WS transmission fluid. Do not even think about a fully synthetic much better etc oil. The Lexus fluid has electrical insulation properties to protect the high voltage electric motors within the transmission. It is not worth the risk of a flash over in the windings of the motors in which case you will need another transmission.

Chris.

Lwerewolf · May 15, 2022

Electrically insulating trans fluid... yeah, uhhh, sorry, no. Especially the factory fill with all the metal wear contamination. Please.

Here's pretty much all you need to know:

https://slideplayer.com/slide/14432904/ (refill instructions starting at page 28 but I suggest that you go through the whole thing)

TL:DR - prius "transmission" with a 2-speed automatic for MG2.

What ultimately matters is that fluid should be barely dripping through the level plug with the engine running at "idle" (~1k rpm - use maintenance mode, for example) and with the ATF temp being between 30c & 40c. Doesn't matter if you're filling it from the oil cooler hose or from the level plug.

You can't change gears at will on this transmission without techstream - going through the virtual gears does practically nothing. There is also a "reset memory" and a "b1 air bleed" (or b2 air bleed?) function.

ayrtonsenna · May 15, 2022

Thank you everyone trying to help me 🙂

I thought and read about the pipe as an inlet for filling in the new fluid, but couldn't find clear confirmation which one is correct ( top or bottom). There is also a biger pipe on the passenger side, which can be a filling point.

I bought genuine Toyota ATF WS fluid, I know we can't change the full amount of transmission fluid, we only make a mix of new an used fluid, with checking of correct level. Thats the reason of troubles if anybody is changing that fluid to anything different. It is a really electrical insulation fluid, electric motor works between 288 - 650 V AC.

Special thanks to Lwerewolf for very interesting slideshow.

Lwerewolf · May 15, 2022

I've been driving with Amsoil ATF for like 100k km already. Conveniently has better copper corrosion characteristics. Plenty of others have swapped, say, a prius' stock trans fluid (conveniently also ATF-WS) for various other ATFs. No reported failures.

I still don't understand how a fluid which is meant to carry fine metal contamination, including clutch pack wear products, can be expected to remain insulating past the "break-in point" of the assembly, but I guess the OEM Toyota fluid is made out of unicorn blood or something.