Hello all. Yesterday I was doing a trail in Bishop. The first 6 miles were a largely flat fire road with a slight incline at times. Got to the steep part, gained about a 1000 feet of elevation in a third of mile when suddenly notice the warning light. Was able to pull off trail immediately and put rig in park.

Didn’t smell anything burning nor find any leaks anywhere. After about five minutes the light went off. Not wanting to take any chances we turned around and went home. Light didn’t come on again during descent nor since.

Was driving in 4wheel high. With AC on. Temps outside in low 90s.

I am always diligent with all service to the rig and take care to keep ride in excellent mechanical condition.

Anybody have experience with this? How big of a concern? What should be of concern or inspected?

I'm curious to know what the actual temp got to. I'm assuming you didn't have a scangauge going at the time so you don't know the temperature? I've been loaded down before and climbing mountains in 100 degrees but never got a high temp warning. Trans temp has gotten up into the 230s and 240s. Since you're light did come on, I would check the tranny fluid to see if it's still good. Once that fluid gets too hot it will break down and not provide the proper cooling/lubricating necessary which will result in future transmission damage and eventually failure. Get it checked ASAP.

Also one thing to note is you should climb at a constant speed in one gear. I do not use "D". Usually it's S4 or S3. That will keep the tranny from hunting and keep the torque converter locked more resulting in less heat buildup in the tranny.

With high daytime temps and a steep hill, maybe 4L would be better.

That happened to me going up to cerro gordo (lone pine) 5k feet climb in 7 miles, consider putting in a tranny cooler

I did Cerro Gordo last weekend and I had no problem. I used 4H and manually navigated between 1st and 2nd all the way up. No AC of course. A guy in a jeep going up overheated and had to stop.

Great stuff here. Thanks.

Will look into scangauge. You have any recommendations?

I use the Amsoil Signature Series ATF (blue top) fluid and add 1/2 bottle of Lubegard Red and this has kept the trans fluid temp down in even the most demanding situations. Not a believer in just use Toyota WS, not saying it’s wrong just better options out there. Toyota 0w20 oil on the other hand is quite amazing. I would also double check your engine coolant and radiator make sure everything is working it’s best to keep everything cool. It could also be the start of a sensor going bad so if it happens with just simple driving from here moving forward you could keep that in mind. Any codes thrown?

Any chance you were going up the access road to Telescope Peak? Was there a lot of wheel slip while you were climbing?


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No. I was about 7 miles or so up- Silver Canyon Road heading up to White Mountains road. Had just gotten to the third or switch back of the steep section, about 3.5 miles from the peak.

No wheel slippage. In fact, the rig was driving great. And driving home to L.A yesterday, there were no issues, despite most of the drive being in about 110 degree weather.

I had the same thought as I was coming down the hill.

5th generation 4runners come standard with a transmission cooler as part of the two package. Are you suggesting an additional one, after market, or something else?

I've seen some Tundra threads similar to this. It looks like long slow uphill climbs in high ambients, in 4 high can lead to this. Many threads on this site and other sites like FJ and ih8mud.

On Tundras the light is triggered at a temp of 302F. This is the AB60F transmission.

On 4runner A750F I believe the light comes on at 302F as well.

The consensus I've read to alleviate this without having to add an aux cooler

4 Lo
4 high in 4S ( to ensure TC lock up schedule is most aggressive)
4 high in 1st for brief periods, 4S

Good thing you knew enough not to shut off the truck and you let it idle for awhile in Park.
I only got my ScanGuage a few months ago. It takes a bit of time and reading to get stuff programmed and it’s pretty limited with only showing 4 gauges at once, but it’s still very much worth it.
At fast highway speeds, 75-90mph, the transmission cruises around 145-175° Depending on ambient. On long steep highway grades in warmer weather I’ve seen over 200° transmission temps but nothing over 210° yet. I always shift to 4th and usually keep it around 65mph on these. I would probably back-off if it gets any higher than that. I can’t even remember what temps I was seeing in 4L , I’ve only done a couple miles at a time so far with the gauge, but I guess it was unremarkable.

This is my jury rigged setup. I’m using a velcro strap around the steering column.

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Had the same exact issue last weekend. The temp was over 100 degrees outside, got the warning on the dash when the temp peaked 300 degrees in the transmission. I had to stop and let it cool down. I was in s3 and 4H. After cooling down went to 4L and the temps stayed down. Needless to say once I got home from the trip I ordered a trans cooler. Going to install it before the next trip, hopefully this fixes the issue.

higher rpms will move the fluid more keeping temps down. Consider an auxiliary cooler to add in line with the OEM one (is the OEM one inside the radiator and acts as a warmer as well for cold climates?)