You should be running above your stall speed on the highway so I'd expect it to run cooler because of that. I use the stock J6 TC which stalls around 1950-2100 and with 3.9 diffs it doesn't often get over that at cruising speeds.
I run at 1850 rpm @ 100 km/h with TC locked and trans temps coming out of the box just plummet.
I run a big Davies Craig cooler in series with the factory TB45E cooler which, btw, is about half the size of the stock ZD30 cooler so my trans temps are always too low unless I'm towing the caravan.
I've had my trans temp gauge hit 120C on one occasion but that doesn't worry me as it's pre cooler temps and I run full synthetic fluid. It drops quickly when I get the chance to hit the TC lockup button.
The factory trans temp warning light comes on at 140C but most agree that that's already too hot for mineral fluid and clutch damage has already started.
John
2001 GUII TI 4500 - Now converted to TD42T auto with Nomad valve body
@jff45 Thanks for the info. I’ll keep a close eye on the temps for this trip and see how she goes. I’ve got about 10’000km to cover, in a variety of highway/desert terrain.
When I get back I’ll have a look and see if I can shoehorn this in https://www.tuffcarparts.com.au/aero...ansmission-oil
I’ll also change the fluid out to synthetic as they used a Dex3 mineral fluid in it.
2016 GU Legend Edition: 3505Kg GVM Upgrade and Stuff!
You can always manage trans temps with the manual TC lockup. Just engage it when not under load and avoid loading it once locked. You'll see the temps drop quickly.
There are those who are happy to keep their TC manually locked during shifts but I avoid it as does the factory behaviour.
Castrol TransmaxZ is considered the best trans fluid but it costs. I use Nulon multi-vehicle synthetic. The important thing is that they flush the whole trans with it, about 12 lts, not just the 4.5 lts in the pan.
John
2001 GUII TI 4500 - Now converted to TD42T auto with Nomad valve body
MB (26th April 2022), stevemc181 (26th April 2022)