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..

 

[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.

 

[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.

 

[co425]

I’ve had zero issues so far. But thanks to OTT for taking a serious look at it. I’ve had issues in the past that were extremely frustrating with other vehicle makes. Their solution was to throw parts at it and see what sticks. This to me is a horrible way to seriously fix a problem. Too much down time and too many days in the shop for no reason.

Unfortunately most companies have zero desire to actually listen to the customer that may know a thing or two. I thank you for taking the time to gather experiences and actually give it a solid go to fix this for people.

 

[24 TRD OR]

I've had it occur on 3 occasions. Twice when I let my son drive who thinks there is some merit in "only using 4wd when you really need it". Those times it occurred in 2wd. I had it occur to myself on a very long sandy hill with my tires aired down below 10 lbs. They are 255/85r17 (pizza cutters) Mickey Thompson Baja Boss. I was in 4wd low and it was about 90 degrees. It occurred within 15 minutes every time. The truck was in D and normal mode every time. I've found switching to 4L and S1, S2 or S3 helps. The occasions with my son the temp was upper 70s and it was just a slow climb, with a few minor obstacles to drive over requiring to go about 5 mph. I have 3-400 lbs of additional weight on that truck all the time. Sometimes more. Every time was 2 passengers, weighing roughly 450 lbs. total. I am planning on getting the Mishimoto transmission cooler as soon as it's available. It's going into cooler weather now, so I hope they have it out before it gets warmer. I do think this is an issue, and that you always have to be thinking about it and remembering "mechanical sympathy". I keep an eye on the trans temp on any hill now. If you would like a "beta tester", I would happily volunteer. Just DM me.

 

[BudBuilt]

• Transfer Case: 4Hi
• Transmission Shifter Position: “D”
• Drive Mode: Normal
• Vehicle Speed: varying from 5–15 mph depending on terrain
• Duration: Had been riding trails for about 2 hours, mostly in 2wd or 4 hi, trans error on dash and had to shut down and wait about 5 min before proceeding in 4lo. Happened 2x. Just used 4lo the rest of the weekend and never had an issue
• Additional Weight: 3-400#
• Tire Size: 37" with stock gears. Regeared to 4.88 and used 4Lo and never had more issues
• Transmission Cooler: Not yet put I plan on it
• Other Details: My first automatic wheeling rig after 54 years of manual experience. Knowing to put it in 4Lo made all the difference. Will install a trans cooler once bumper is done. Would love a software solution too.

 

[grizzlyoutlaw]

@JustDSM I am tuned from your guy at High Country Tuning. This truck sees daily usage offroad and gets pushed to find the limits. I dont think ambient temperature has as much to do with it. Its also not an issue with slower obstacle focused 4WD usage. It seems more agitated by variation like my two examples.

Red zome temperatures.

• Transfer Case: 4HI
• Transmission Shifter Position: Manual selection - Typically 2-3
• Drive Mode: Sport with some dirt mode
• Vehicle Speed: varying from 10-40MPH
• Duration: 45 minutes
• Additional Weight: 800 LBS
• Tire Size: 285/75/R17 Falken Wildpeak AT4W C Rated
• Transmission Cooler: none aftermarket.
• Other Details: 1 hour of highway driving 500' elevation gain. Followed by 45 minutes of windy washout and switch backed 2500' elevation gain. Stopped when I noticed the transmission hitting red. Very spirited rally style driving. 4HI was used for traction on rocky loose road surface. IE slow way down - washout ruts/switchback then accelerating out. This is where it happens.

limp mode activated

• Transfer Case: 2HI - Some 4HI
• Transmission Shifter Position: D
• Drive Mode: Towing
• Vehicle Speed/Duration: Through city. alternating between stopped to 45 MPH.
• Duration: 15 miles 30 -40 minutes
• Additional Weight: 6K dump trailer
• Tire Size: 285/75/R17 Falken Wildpeak AT4W C Rated
• Transmission Cooler: none aftermarket.
• Other Details: Towing trailer across town. Not watching temps since it was 15 miles. At the end I had to back the trailer up a gravel incline around a corner into a tight spot. Took multiple attemps at going forward, then reversing, maybe 40 feet. May have used 4WD to stop wheel slippage. That high load on converter caused full limp mode activation for cool down.

 

[lfe]

2024 Tacoma TRD Pro

1st occurrence (limp mode)

• Transfer Case: 4Hi
• Transmission Shifter Position: “D”
• Drive Mode: Normal
• Vehicle Speed: 5mph average
• Duration: 15 minutes - was barely a quarter mile into the trail
• Additional Weight: 900 pounds of payload
• Tire Size: OEM
• Transmission Cooler: N.
• Other Details:
  • https://webmap.onxmaps.com/offroad/...&link_id=01K6G6DHTT9K9F5ECX69HSD18G&mode=dirt
  • Ambient temp ~45*F

2nd occurrence (limp mode)

• Transfer Case: 4Hi
• Transmission Shifter Position: “D”
• Drive Mode: Normal
• Vehicle Speed: 5 mph
• Duration: 25 minutes
• Additional Weight: 1600 pounds of payload
• Tire Size: 35x12.5r17 Toyo R/T Pro
• Transmission Cooler: N
• Other Details:
  • https://webmap.onxmaps.com/offroad/...?link_id=01K6G6N8VYE23CPX11M94F3VH5&mode=dirt
  • (From Highway 88)
  • Ambient temp ~65*F

3rd occurrence (temp gauge at max, but no limp mode)

• Transfer Case: 4Lo
• Transmission Shifter Position: “D”
• Drive Mode: Normal
• Vehicle Speed: 15mph
• Duration: 45 minutes
• Additional Weight: 1300 pounds of payload
• Tire Size: 35x12.5r17 Toyo R/T Pro
• Transmission Cooler: N
• Other Details:
  • https://webmap.onxmaps.com/offroad/...FGWVX5XY0&mode=dirt#12.32/39.05631/-119.84881
  • Took the trail from north to south
  • Drove up to Genoa Peak
  • Kept it in 4Lo from the very start
  • Temps were steadily climbing - when I reached the peak the temp bar looked maxed to me and I expected the temperate warning light to trip but I guess I made it just in time
  • Ambient temp ~75*F

Quite a few outings in between these occurrences and a few notes on how I've been avoiding this being a regular thing:

1. After the 1st occurrence, I came here and read of the other reports of overheating issues so I've been mindful of it ever since.
2. Between the 1st and 2nd occurrence, I tried to keep using 4Hi as much as possible but I spent just as much time staring at my trans temp gauge as I did looking where I was going on trail (needless to say, I was going SLOW) and temps were still spiking. I'd come to a stop and let the temps drop before continuing. I tried manually shifting to no avail.
3. After the 2nd occurrence, I've resolved to only using 4Lo if I need 4x4 and I'm off the highway.
4. Most of my wheeling involves a lot of stopping and spotting (for myself and other group members), so I'm watching the temp gauge hover around 75%, but it gets time to sit and cool off pretty frequently - in general, I'd say trans temps are always an issue, but I've been working around it.

 

[lfe]

>A 1000ft rise over 1.3 miles is a very steep grade, comparable to a 14%

So the beginning of the trail there is super steep but the average is 10% grade, which is pretty steep but not as crazy as 14.

Probably a 4Lo situation.

Note that this was less than a quarter mile into the trail - maybe 200 feet of elevation gain at that point. So several notes:

1. After I hit limp mode and let it sit for a while (20+ minutes) I shifted to 4Lo and continued up the rest of the trail. I had to stop every 10-15 minutes and let it cool because the temp gauge was pegging near max.
2. Was my first time wheeling this truck, but have been building and wheeling stuff for 15 years now - 4hi would have sufficed for 90% of rigs. The two groups coming down as I was headed in had made it up in 4Hi without lockers and were a mix of 2nd and 3rd gen tacos, gladiators, and 3rd and 4th gen 4runners

 

[JustDSM]

*ATTENTION*

This isn't a discussion post. If you want to chit-chat about this topic please create another thread for that purpose.

Posts that are not relevant to the original question will be deleted.

Thank you for keeping this On-Topic. There are enough dumpster fire posts regarding this, so it won't become another.

Thank you,
Justin

 

[thedaypa]

Hey OTT,

Thanks for posting this and looking into the problem. Sorry in advance for the long post. I have some experience with this issue so I figured I would chime in hopes there is a software fix you guys can come up with for this. OR maybe to provide a temporary solution to anyone who is in a similar situation.

I have never actually overheated and entered limp mode as others have. I monitor the temps closely and pull over if necessary. I do not tow so for me this is mainly been an issue while off roading, but I'd have to say, its happened to me on some pretty simple trails.

My truck is a 2025 Off Road - non hybrid, with about 5k miles on it right now. In it's current state, it sits on 35's and has the OTT Tune done by Q here in Southern CA.

Most of my experience with the truck reaching high temps was when it was in its stock state.
That said, I was still getting to know it then and believe the trans would still hit higher temps and overheat with my current mods. I have seen the temps climb a bit on trails since completing my mods, but I have just learned how to adjust my driving style accordingly to prevent this from happening. Although I'm sure it is slightly affecting it, I've really not seen any significant trans temp differences due to 35's for anyone wondering.

It's worth noting that I did perform a break in period for the first 1k miles on the truck and did not have it off road during the initial break in. At 1k I performed the first oil change and started hitting some trails.

Here is my experience with the truck in it's stock state.

• Transfer Case: Temps rise in 2Hi and in 4Hi, never 4Lo
• Transmission Shifter Position: Temps are an issue in D in both 2Hi and 4Hi. If you manually control shifting in 4Hi, and stay in in lowest gear possible (usually just S1 and S2) trying to keep RPMS between 2k-3k, it's good. Anything off road, while climbing, with ambient temps above 80 degrees, 2Hi begins to overheat whether you're in D or S shifting mode.
• Drive Mode: Normal
• Vehicle Speed: 5-20 mph through forrest road
• Duration: 10-15 mins into the drive, 2.2 miles on OnX, about 900 ft elevations change (map below)
• Additional Weight: 200 lbs (camping gear, dog, girlfriend)
• Tire Size: OE.
• Transmission Cooler: N
• Other Details:

Coming from my old 2nd gen Tacoma with an UltraGauge installed, if I saw temps above 235ish, I would start to consider pulling over and letting her cool. 250 was the hard stop on that truck for me. This was a rarity in the 2nd gen.

In the 2nd gen, I would commonly do trails in 2WD and only shift into 4 if necessary. In the 4th gen, I've learned, DO NOT do trails in 2WD. If you are on dirt, it needs to be in 4WD and shifted manually or the temps begin to rise. I feel for those who tow with these trucks and need to keep them in 2WD while towing up a grade.

I also found this video very helpful/interesting from TFL. Their gauge is reading temps into the 270's and it hasn't overheated yet. Clearly these 4th gens and the oils being used are capable of handling much higher temps than previous gens.
.

I first noticed my temp issues on the Black Mountain trail outside of Idyllwild, CA. It was a hot day, about 95-100 when coming up the mountain roads, and about 85 when we reached dirt and got on the trail. This was the trucks 2nd time out for a quick overnight camping trip. It's first trip was the week before. I drove it up Coxey road on the back side of Big Bear CA, in even warmer temps, alternating between 2Hi and 4Hi, in D position, and did not experience this issue. Weird, but that trail has a bit less grade to it.

On Black Mountain, I had the truck in 2WD since the trail is quite easy. There is some grade to it and it slowly switch backs up the mountain. Only about 10-15 mins into the drive and 2.2 miles according to OnX, the trans temp display in my gauge cluster was getting very close to the redline, prob about an 8th of an inch away from redline on the gauge. By referencing the TFL video above, I would estimate I was around about 260-270 degrees at that time. I pulled over and let it cool for about 5-10 mins. That location is the end point of the red line on the map below.

When we resumed the trail still in 2WD, the temps quickly rose back to that same position, and it felt as if the gears were slipping a a bit, so I pulled over again to cool. As we resumed again, I shifted to 4WD and left it in the D position, although slightly better, the temps rose quickly again so we pulled over. Finally as we neared the first group of yellow post sites of that trail, I figured out that if I had it in 4Hi and kept in mainly in S1 and S2 as needed, the temps would stay in check and not rise further. Since the trans was already hot, I was never able to get the temps back to the center position under the gear icon in the cluster, but I was able to keep them from rising further as we made our way to the end of the trail and camp. Coming down the mountain the next day, I did not have any issues.

I was bummed after this trip. My mind quickly raced to the worst case and horror stories I had heard about the 4th gens transmission issues. I called Toyota just to document the issue while the truck was in it's stock state so I that I would have some proof of the issue being present before the mods I had planned were complete.

The next week, we ended up back at the exact same trail in ever warmer temps so turned out being a really good opportunity to test of the issue again in almost identical conditions. This time, I kept it in 4Hi from the beginning but in the D position to start. Temps again rose, not as high as the previous week, but I'd say about 75% of the gauge was full. Once I changed into S mode and shifted between S1 and S2 accordingly, I was able to normalize the temps in the gauge and complete the trail without even coming close to overheating. I had my buddy behind me in his 24 TRD Sport iForce Max Hybrid, and his temps were doing the exact same thing as mine. We both shifted manually to keep the temps in check.

Since performing my mods which include true 35 x 12.5 E load Toyo RT Pros, full sliders, skids, OTT tune, CB exhaust, etc... I have seen temps get slightly above there center position on the gauge, maybe just to the right side of the little gear icon or slightly beyond that, but no higher. So I believe the same issue would arise again, but I have just learned to shift manually and make sure I am in at minimum in 4Hi while off road to avoid it. Several more trips deep now and have not experienced anything close to overheating while driving like this in above 80 degree temps, up steep grades, for long durations up to 8-10 hours days.

On road, I've driven up many of our steeper passes here in Southern CA like the Grapevine and Cajon pass, as well as many mountain roads, all under the same load of about 200 lbs, and have not seen the temps go past the gear icon. I've only experienced one issue on road which was on a pass which is called Nine Mile Canyon that leads up to the Kennedy Meadows area. It goes from about 2k feet to around 7k very quickly and in 2Hi, I did see the temps begin to rise. I put it in S mode and just made sure I was in the lowest gear without getting the RPMs too high and although it was getting hot, I did not exceed I would say that 75% mark on the trans gauge. The higher speeds and air flow we get on road I imagine are helping out tremendously with keeping temp in check. It was also hot this day. About 100 in the valley below, then dropped to 75 by the time we hit the Kennedy Meadows area.

One thing that stood out to me is that anytime you are in 2Hi or 4Hi at lower speeds (under 20), while off road, if you shift from the D position to S, it always shows I'm in 3rd gear. Whether I starting from a complete stop or have some momentum already. If that's truly the case and it's actually in 3rd gear, then I can see that engine and trans are working too hard to generate the torque needed on trails and that is why the temps rise so fast. The truck needs to default to the appropriate lower gear in these situations and do it normally in D mode.

All this to say that this issue can be managed with manually shifting and adjusting your driving style in these 4th gens. Do I think we should have to do that. Absolutely not! I hope you guys can find a fix for us.

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