Taking a Deeper Look at Transmission Overheating in 4Hi

[JustDSM]

Hey everyone,

We’ve been following the discussions around transmission overheating—particularly when operating in 4Hi—as highlighted in these threads and others:

• 2024 Tacoma Transmission Overheating on Long Climbs Off-Road
• Transmission Overheating in 4Hi When Going Uphill – Toyota’s Answer (or Non-Answer)
• 2025 4Runner Transmission Overheating on Climbs Off-Road

We (OTT) want to take a deeper dive into this issue, as it’s clearly affecting a number of owners in the community. While adding a transmission cooler is certainly one part of the equation, we’re also exploring whether software-oriented changes could provide a meaningful improvement or potential "fix".

We've been evaluating some changes behind the scenes, but we'd like to better understand where/how this happened to you. As such, we’d love to gather more real-world data from those of you who have personally experienced the overheat condition in 4Hi (or 2Hi if applicable). If you’re willing to share, the following details would be extremely helpful:

• Transfer Case: 2Hi, 4Hi, or 4Lo
• Transmission Shifter Position: “D” or manual selection (S1, S2, S3, etc.)
• Drive Mode: Normal, Eco, Sport, etc.
• Vehicle Speed: An average speed is great, but more detail like “~15 mph most of the time, varying from 5–20 mph depending on terrain” is even better.
• Duration: Approximately how long you were operating in that state before the overheat occurred.
• Additional Weight: Estimate of weight over stock (aftermarket gear, camping equipment, etc.) present at the time.
• Tire Size: If different than OE.
• Transmission Cooler: Fitted Y/N.
• Other Details: Anything else you think is relevant or noteworthy.

The more detail the better—we want to look for common threads and contributing factors.

Thank you in advance for helping us compile this information. We’re optimistic that with sufficient community feedback, we can gain a deeper understanding of the problem and explore a comprehensive solution that extends beyond just hardware.


—OTT

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[Rock Doc]

Having the same issues, 2Hi shifter in D drive in normal mode driving speed under 10 mph going uphill beginner trail green on OnX for 20 min or so but short stops in that time. I am the only person in the vehicle no additional weight stock vehicle the temp seems to get to about 3/4 on the trans temp gauge so last time pulled over and sat for 15 min or so and cooled down rest of trail flat and no issues and driving TRD Pro.

 

[AdFour]

I'd add ambient temp to your list up top. Approx +/-5 deg would suffice.
Elevation too

 

[porkyfly]

Just curious, wouldn’t manually holding a lower gear (or maybe switching to sport mode) fix the issue? The issue (correct me if im wrong) appears to be the transmission holding too high of a gear, resulting in continuous torque converter slippage. I suppose it could also result from the failure of the TC to lock up.

Would it be a good idea to monitor engine RPM and load aswell to ensure an appropriate gear is selected?

 

[timelapse]

I recently repeated the same 3,000 vertical climb outside of Silverton CO. 2 days apart. I'll provide details for my findings as I used this as an opportunity to experiment with the overheating. Worth noting, I've done this one numerous times in my 5th gen with oversized tires and 4Hi or 2WD and had no issues with temps.


3,000' climb on gravel and loose rock: Attempt #1

• Transfer Case: 2Hi and 4Hi
• Transmission Shifter Position: “D”
• Drive Mode: Normal but as we climbed higher, tried to stay in lower gears manually
• Vehicle Speed: ~10-15 mph most of the time, varying from 5–20 mph depending on terrain
• Duration: Transmission temp started to increase past the normal middle within the first 200 vertical feet. Almost instantly. Total climb time was maybe 15 min?
• Additional Weight: no back seat, mostly empty inside. 1 passenger. 2 mountain bikes on 1up rack.
• Tire Size: KO3 275/70/18, e rated 25lbs over stock weight per tire
• Transmission Cooler: Nope
• Other Details: Visible heat increase on the gauge. Never let it overheat or trigger a warning. Had to stop along the way. Ambient temps 70->50 F

3,000' climb on gravel and loose rock: Attempt #2

• Transfer Case: 4Lo
• Transmission Shifter Position: “D”
• Drive Mode: Normal.
• Vehicle Speed: ~10mph most of the time, forced to stay at lower speed even when it wasn't required
• Duration: Transmission temp started to increase past the normal middle within the first 200 vertical feet. Almost instantly.
• Additional Weight: no back seat, loaded down with some camping gear this time. 1 passenger. 2 mountain bikes on 1up rack.
• Tire Size: KO3 275/70/18, e rated 25lbs over stock weight per tire
• Transmission Cooler: Nope
• Other Details: No stopping, no overheating. Only downside was slower speeds due to 4Lo when it wasn't really necessary. Ambient temps 70->50 F. Photo is from the way back down after it rained.

 

[windjunkie]

I did a slow uphill in 4 hi. Hybrid orp. 285/70/17. 2 hours under 5 mph. 4 passengers. In D, drive mode normal. No overheating

 

[timelapse]

I did a slow uphill in 4 hi. Hybrid orp. 285/70/17. 2 hours under 5 mph. 4 passengers. In D, drive mode normal. No overheating

That's good news. How much vertical did you climb in 2 hours? Trans temp didn't budge past the middle? 5mph in 4Hi is very slow lol

 

[Dog4Runner]

Just curious, wouldn’t manually holding a lower gear (or maybe switching to sport mode) fix the issue? The issue (correct me if im wrong) appears to be the transmission holding too high of a gear, resulting in continuous torque converter slippage. I suppose it could also result from the failure of the TC to lock up.

Would it be a good idea to monitor engine RPM and load aswell to ensure an appropriate gear is selected?

That's exactly how they taught us to use 4L years ago. If not it caused overheating.

 

[k9Hiken]

Just curious, wouldn’t manually holding a lower gear (or maybe switching to sport mode) fix the issue? The issue (correct me if im wrong) appears to be the transmission holding too high of a gear, resulting in continuous torque converter slippage. I suppose it could also result from the failure of the TC to lock up.

Would it be a good idea to monitor engine RPM and load aswell to ensure an appropriate gear is selected?

From my understanding that is what owners are being told to do. Manually shift it instead of leaving it in one gear.

 

[timelapse]

From my understanding that is what owners are being told to do. Manually shift it instead of leaving it in one gear.

Yep that will help. It's mostly just annoying for anyone who switched from a 5th gen. You didn't have to think about any of that with the prior gen. Everything just worked.

 

[Rock Doc]

I also watched a video explaining that you should use 4low for that reason will try that on my next trip.

 

[porkyfly]

Yep that will help. It's mostly just annoying for anyone who switched from a 5th gen. You didn't have to think about any of that with the prior gen. Everything just worked.

I agree this issue is annoying and absolutely should not happen. This needs to be resolved by Toyota ASAP free of charge.

I was just guessing the issue is most likely software related, whether it’s failure to stay in an appropriately low gear or failure to lock up the TC. It is very unlikely that the transmission cooling system is mechanically inadequate.

 

[6GenChad]

Hey everyone,

We’ve been following the discussions around transmission overheating—particularly when operating in 4Hi—as highlighted in these threads and others:

• 2024 Tacoma Transmission Overheating on Long Climbs Off-Road
• Transmission Overheating in 4Hi When Going Uphill – Toyota’s Answer (or Non-Answer)
• 2025 4Runner Transmission Overheating on Climbs Off-Road

We (OTT) want to take a deeper dive into this issue, as it’s clearly affecting a number of owners in the community. While adding a transmission cooler is certainly one part of the equation, we’re also exploring whether software-oriented changes could provide a meaningful improvement or potential "fix".

We've been evaluating some changes behind the scenes, but we'd like to better understand where/how this happened to you. As such, we’d love to gather more real-world data from those of you who have personally experienced the overheat condition in 4Hi (or 2Hi if applicable). If you’re willing to share, the following details would be extremely helpful:

• Transfer Case: 2Hi, 4Hi, or 4Lo
• Transmission Shifter Position: “D” or manual selection (S1, S2, S3, etc.)
• Drive Mode: Normal, Eco, Sport, etc.
• Vehicle Speed: An average speed is great, but more detail like “~15 mph most of the time, varying from 5–20 mph depending on terrain” is even better.
• Duration: Approximately how long you were operating in that state before the overheat occurred.
• Additional Weight: Estimate of weight over stock (aftermarket gear, camping equipment, etc.) present at the time.
• Tire Size: If different than OE.
• Transmission Cooler: Fitted Y/N.
• Other Details: Anything else you think is relevant or noteworthy.

The more detail the better—we want to look for common threads and contributing factors.

Thank you in advance for helping us compile this information. We’re optimistic that with sufficient community feedback, we can gain a deeper understanding of the problem and explore a comprehensive solution that extends beyond just hardware.


—OTT

Took my TRD ORP on a moderate trail.

Transfer Case: 4Hi

Drive Mode: Had it normal with MTS on auto

Speed: I averaged about 9-13 MPH on the trail

Duration: Temps started to climb as I we got higher in elevation. Around the 3,000 mark. As soon as I got to the 4500 mark, it was climbing high and almost into the red. I switch to 4Lo and temp started to go down.

Weight: Besides myself and recovery, no additional weight.

Tire Size: Stocks Falken’s 265/70/18

Trans Cooler: No

I wasn’t going over any crazy obstacles. Had my air own on low and one bar of power with a temp of 89° outside.

 

[Vincenzo]

I will start by saying this is my very first four wheel drive vehicle. The boat ramp will most likely be the only time I use it. No one has mentioned what degree of incline they‘ve been navigating. There might be a multitude of factors contributing to this problem. I’m curious to know if those shutters are open or closed when the overheat is occurring. Is it torque converter slip? Does it require a larger transmission cooler or a supplemental one? Increased fan size? It appears that the engineers failed to put the vehicle through the proper paces. Right now, I think 4Lo is your friend. I have a ScanGauge that monitors engine parameters. It works well. The factory temp gauge is a joke.

 

[timelapse]

I agree this issue is annoying and absolutely should not happen. This needs to be resolved by Toyota ASAP free of charge.

I was just guessing the issue is most likely software related, whether it’s failure to stay in an appropriately low gear or failure to lock up the TC. It is very unlikely that the transmission cooling system is mechanically inadequate.

Agreed— this on Toyota. I’m not going to pay for an OTT tune. If an old Prius can fly up a 2000’ ft gravel forest service road without issues yet a 2025 4R needs to go slowly in 4Lo or manually keep the transmission in lower gears, it’s just embarrassing.

Luckily, I haven’t had any issues going up bigger paved climbs yet.

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