A/T overheating. (1 Viewer)

[Glenn Bartlett]

Was towing my boat (2 tonnes double axle trailer) long distance recently with my '92 HD-T auto. There's one very steep and long hill on the trip. Was crawling between 2nd and 3rd gear for most of the hill keeping revs at about 2200. About 2 kms from the top the A/T temp warning light came on. I couldn't stop (no kerb) so pressed on till I got to the top but was a bit worried. But all has seemed well subsequently.
I only do this trip once or twice a year so dont really want to go to the extent of a transmission cooler. Am I likely to do damage with this brief temperature overload?

The tranny is a 4 stage auto, it seems the 4th gear is a lockup overdrive gear (thats what it sounds and feels like). Am I right that overheating is caused by slip in the viscous coupling under load? If this is the case would it be better to move to low ratio and try to get into locked 4th gear to prevent slip? Would this prevent overheating? or am I talking noobspeak?

BTW all the other 80s I have driven have a 3 stage auto with a button activated O/D. Is this the same tranny as the 4 stage but with a different shift mech or a totally different tranny?

 

[lacruiser]

Heat is the biggest killer of automatic transmissions, so you definitely want to avoid this situation. By getting the fluid hot, you've greatly decreased its service life. You need to get that fluid out of there.

First off, do the "rodney flush" (search here on mud for the procedure) and by all means, USE SYNTHETIC FLUID. It's much more heat-resistant. Amsoil is good, there are others.

Yes, dropping down to a lower gear will help a lot, even in high range in say, 2nd gear (if necessary), you're generating a lot less heat then you are (at the same speed and load) if you're in 3rd gear.

I don't know if the trans locks up the Torque converter in low range, never actually tried that. If it does, sure, you could hit low range and 4th gear, why not?

Yes, overheating ATF comes primarily from slip inside the torque converter. lockup will mostly eliminate that source of heat.

Don't know which trans you've got. What market is the truck from? (where are you located?) Mine is also the 4th gear with no overdrive button, and it's a fully-hydraulic unit (no computers, non-electronic).

 

[Glenn Bartlett]

Cheers for that, are you saying that the tranny fluid will be screwed up by overheating and no longer function correctly? Do some tranny fluids have higher operating temperature tolerances?
Its a ex Jap truck (I'm in New Zealand). Same as yours I guess. No computers or electronics.

 

[lacruiser]

Ok, then you've got the fully-hydraulic A442F probably.

Yes, the high heat will oxidize the fluid and kill some of it's protective properties. You should change it.

Rodney is close to you, in OZ, he's a wizard with these auto boxes, and a fount of knowledge.

Wholesale Automatic Transmissions

He also recommends synthetic fluid. You may want to inquire about his extreme valve body. Folks here who've used it swear by it.

that, along with a good thorough exchange of fluid with synthetic will probably be fine for you.

 

[7schulz]

Use TranSynd it's the best HD syn transmission fluid on the market. Allison Transmission recomends TranSynd for all their transmissions. It will hold up better to the heat.

 

[ShawnTRD]

All oil loses some quality from being overheated. When is the last time you changed the fluid? If you have to think about it, it's time to change it. Like lancruiser said you best to do the flush.

https://forum.ih8mud.com/80-series-tech/19299-transmission-fluid-exchange-writeup.html

 

[Cañonero]

Mine is also a 1991 HDJ81 with the hydraulic A442F.

I've had similar problems and you already got the best advices:

1- Change to FULLY synthetic fluid.

2- Fit in the biggest aftermarket cooler you can. I have Tru Cool Max and it's cheap and cools the hell out of it, Rodney also sells very good quality coolers, more expensive in my case, that's why I got tru-cool max, but being in New Zealand, you may be better with his.

3- Consider Rodney's extreme Valve body kit and transmission temperature gauge (this last one saved me from blowing mine again).

Check this out:

https://forum.ih8mud.com/80-series-tech/261256-transmission-oil-temperature-problem.html

https://forum.ih8mud.com/80-series-tech/351778-toyota-atf-type-t-iv.html

 

[Glenn Bartlett]

Shawn I've only had the truck <6 months. Its done 235000 kms and I have no service history because I bought it from a dealer who had traded it but its in good nick in general. I'm getting the front axle serviced next week, so I'm working thru the various items that probably need to be serviced. The tranny fluid looks OK, its red with no smell, no residue or fragments on the dipstick so I'm wondering how critical the change really is. That link to the tranny fluid exchange seems a bit of a stopgap as I would have thought that if there is any residue from wear or overheating it would collect in the tranny pan, and wouldnt necessarily flush out without a full dismantle. Also you can't change the filter unless its pulled apart. I think I'll see if I can get the guys to do a tranny filter and fluid change when they do the axle. Should probably do both myself but I've got a mechanical warranty for 3 years that stipulates only qualified mechanics do the servicing/maintainance.
Thanks for everyones help -this site rocks.

 

[Glenn Bartlett]

Hmmm, after reading all this stuff it seems I should also fork out for a tranny oil cooler before I do some damage.

 

[Scalci]

Hi, I have the same issue, and everyone told me to do the Valvle Body conversion that Rodney have. I am saving up now to do this. I have an aftermarket Oil cooler on, but it still overheat, but I am also saving to get the Tru-Max one from the USa.

 

[Tools R Us]

The US (not sure of other markets) FZJ80's came with a very nice trans cooler setup. It is very well mounted and proven, if this factory setup is available (used?) it would be my first choice for an upgrade.

 

[Glenn Bartlett]

Scalci, what sort of coin are you looking at for the valve body kit?

 

[Scalci]

Hi, the valve body cost about $750 Aus. While I got my transmission overhauled, I asked them to fit the valve body as-well. But I still have cooling issues. The previous owner fitted an aftermarket oil cooler, because the LC’s in the UK did not come with an oil cooler, So I stay in South Africa and the temperature is quite hot by nature.


Can someone please post a photo of the original Toyota cooler and where did they mount it?

 

[Scalci]

We took the tranny out again, and can't see any issue with the overheating. I removed the valve body and will send it back, as I could not feel any difference, under load or pulling my trailer.

I got another tranny and will install that with a new torque converter to see if that solves the issue.

What is happening, when I drive in traffic, and the tranny switch from 2 to 3rd, it overheats, when it is in final drive it is fine... So I don’t know anymore..

 

[mmuthart]

We took the tranny out again, and can't see any issue with the overheating. I removed the valve body and will send it back, as I could not feel any difference, under load or pulling my trailer.

I got another tranny and will install that with a new torque converter to see if that solves the issue.

What is happening, when I drive in traffic, and the tranny switch from 2 to 3rd, it overheats, when it is in final drive it is fine... So I don’t know anymore..

The Extreme Valve Body from Wholesale will let the torque converter lock in 3rd gear. Typically when the tranny down shifts to 3rd (like when climbing a grade on the highway), the torque converter unlocks and generates a ton of heat. The 3rd gear lock up is very noticeable and easy to detect when starting from a stop. When the torque converter locks it feels like another gear, RPM's will drop a couple hundred RPM.

If your tranny fluid is getting super hot while in 3rd gear, sounds like the 3rd gear lock up is not working as you suspect. I'd want a tranny fluid temp gauge to verify that's what is happening...

 

[Scalci]

The Extreme Valve Body from Wholesale will let the torque converter lock in 3rd gear. Typically when the tranny down shifts to 3rd (like when climbing a grade on the highway), the torque converter unlocks and generates a ton of heat. The 3rd gear lock up is very noticeable and easy to detect when starting from a stop. When the torque converter locks it feels like another gear, RPM's will drop a couple hundred RPM.

If your tranny fluid is getting super hot while in 3rd gear, sounds like the 3rd gear lock up is not working as you suspect. I'd want a tranny fluid temp gauge to verify that's what is happening...

This is why I am not happy with the valve body, mine does not lock in 3rd gear... the moment my tranny gears down to 3rd gear, the tranny overheat...

I spoke to Rodney and he say I must send it back, but the issue I have I dont have a spare valve body. That forced me to buy another tranny...

I have the temp gauge from Rodney on, the temp goes over 150 Deg C....