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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[Vidman]

So great that OTT is looking to possibly sort out the trans overheating issue.. that would be a game changer for the people that have had issues. I have had no issues as of yet so I cannot contribute any info at this time good luck getting something in one of your tunes that will solve the problem..

 

[james cole]

Subds!

 

[tacorancher]

Never been an issue for me, but I have not really loaded my truck up that much and I’ve also maintained a wheel entire package that is roughly the same diameter and weight as OEM. I’ve checked the temperature many times using the OBD port during strenuous 4 hi off-roading for several hours in the Texas heat, and never a single problem. I think the highest I’ve seen is 230.

 

[james cole]

@JustDSM can you also take a look at the Transmission feeling like a cvt or an old 80s 4 speed?

This feeling might be connected to high temps, as you guys know too smooth of a transmission leads to heat and accelerated wear.

Thanks!

 

[wire4money]

@JustDSM can you also take a look at the Transmission feeling like a cvt or an old 80s 4 speed?

This feeling might be connected to high temps, as you guys know too smooth of a transmission leads to heat and accelerated wear.

Thanks!

This is the high stall torque converter. I believe this is why some are having trans overheat messages.

 

[MT-Taco]

3 days and counting in MOAB. Zero overheating issues. I’m not trying to be rude but the issue is user error. 29K miles probably 10K is in dirt and never had a problem! You just need to know when and what to use 2, 4Hi, or 4Lo.

 

[izzy]

Figured I'd contribute, since the unmentionable other site has.. issues.

• Transfer Case: 2Hi, 4Hi, or 4Lo - 2Hi then 4Hi, then 4Lo
• Transmission Shifter Position: “D” or manual selection (S1, S2, S3, etc.) - S2 in 2Hi, S1 in 4Hi, D in 4Lo
• Drive Mode: Normal, Eco, Sport, etc. - No drive mode options on SR
• 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. - Trail was 10mph towards the bottom and 5-7 mph towards the top
• Duration: Approximately how long you were operating in that state before the overheat occurred. - Entire drive was 4hr, no overheat occured
• Additional Weight: Estimate of weight over stock (aftermarket gear, camping equipment, etc.) present at the time. - Full CBI skids, one passenger, some water, Diode light rig, maybe 200lb of stuff, full tank of gas
• Tire Size: If different than OE. - 265/70/17
• Transmission Cooler: Fitted Y/N. - N
• Other Details: Ambient temp was about 87, saw 85 to 90F depending on where we were on the mountain.

Orange section on map was 2Hi, poorly paved road/dirt, black dot was the switch to 4Lo when trans temp hit 240F. Trans temp stayed 230F when in 4Lo to the peak. So 1560ft in 3.9mi (elevation and distance) at the black caused the trans temp to hit 240F in mix of 2Hi/4Hi. Approx 7% grade at 10mph.

I'm not really interested in aftermarket solutions here for this but hopefully this data is useful. Just interested to see what you guys find out

First half of this is correct, after the peak the app died.

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