More overheating after dealership visit :(

[joebangle]

So we went to the dealership and explained the overheating transmission concerns driving up mt. washingron which is a paved road with multiple switch backs making 4low risky with drive train binding.
The dealership cleaned off the exterior transmission thermostat because of oil undercoating possibly causing binding? This wasn't covered under warranty of course and was $360. They did say it was refundable if it didn't fix the issue which is good.
Now we drove up mt pack Monadnock which is much less severe but is still paved with multiple switchbacks and the transmission overheated again. It was a sunny 60F day driving up in drive in normal mode with extra light throttle not pushing the engine whatsoever with a 9 year old in the back seat. It took 21 minutes revving the engine in park to bring the transmission temps back down to the middle. If I could switch to 4low without the binding I would have, but these trucks don't allow disengaging the front hubs like the old trucks.
I'm going back to the dealership next week, but I don't know if this is a transmission issue, or programming issue, or cooler issue. The master mechanic said when he tested the transmission the temps spiked up quickly, but the fluid didn't look burned etc when I brought it in originally. I'm worried for obviously the life of the drive train, being able to use the truck for actual work, and to be able to bring my little one on these fun trips with the family. This was one of the big reasons we bought the trd offroad non hybrid model....

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[Tacoma John]

Very interested to hear how this goes. Looking forward to updates. Thanks for sharing.

 

[Cappaworks]

Keep in mind that with an automatic transmission, lower engine RPM will generally create more heat in the transmission when climbing grades. So lugging gears will cause more transmission slip and heat. On long grades, you are usually better off manually selecting a lower gear with a slightly higher engine RPM than taking it easy and lugging the engine and transmission. The higher engine RPM helps in two ways. It develops more transmission pressure and volume pushing through the cooler and the transmission is able to lockup instead of slip. The cooling fan is electric so the higher engine RPM will not increase airflow over the transmission oil cooler.

 

[djevans]

So we went to the dealership and explained the overheating transmission concerns driving up mt. washingron which is a paved road with multiple switch backs making 4low risky with drive train binding.
The dealership cleaned off the exterior transmission thermostat because of oil undercoating possibly causing binding? This wasn't covered under warranty of course and was $360. They did say it was refundable if it didn't fix the issue which is good.
Now we drove up mt pack Monadnock which is much less severe but is still paved with multiple switchbacks and the transmission overheated again. It was a sunny 60F day driving up in drive in normal mode with extra light throttle not pushing the engine whatsoever with a 9 year old in the back seat. It took 21 minutes revving the engine in park to bring the transmission temps back down to the middle. If I could switch to 4low without the binding I would have, but these trucks don't allow disengaging the front hubs like the old trucks.
I'm going back to the dealership next week, but I don't know if this is a transmission issue, or programming issue, or cooler issue. The master mechanic said when he tested the transmission the temps spiked up quickly, but the fluid didn't look burned etc when I brought it in originally. I'm worried for obviously the life of the drive train, being able to use the truck for actual work, and to be able to bring my little one on these fun trips with the family. This was one of the big reasons we bought the trd offroad non hybrid model....

I don’t know that yours is the same problem as mine, but it certainly could be. I have a 2025 Tacoma Ltd. I was towing roughly 5800 pounds. All of mine was fairly flat interstate in middle Tennessee. I was heading east to Gatlinburg from Nashville if you’re familiar with the road. It’s nothing like Nashville to Chattanooga. But anyway, I got about 30 minutes into the trip and I got a heat warning, “transmission only”
on the dash. I was able to pull over easily and wait at a few minutes. The temperature dropped and I tried to go on. I got an overheat warning again, even though I was driving extremely light footed. So we turned around and went back and got another vehicle. (I had to stop four times to let it cool down. I took it in. They kept it three or four days. I haven’t pulled with it since so I don’t know if it’s truly fixed, but this is what they found and apparently it wasn’t easy for them to locate. Oh, and they had to wait for a specialist to come in so keep that in mind.

Ok, don’t shoot the messenger, this is what they told me.:” P070513 found internally shorted Park neutral switch, not allowing proper adjustment for TCM to determine when vehicle was in drive - 832131 Park neutral position switch assembly was replaced”

They literally said the TCM couldn’t determine what gear it was in and somehow that overheated either the torque converter or somehow overheated the fluid in some other way.

Just throwing it out for whatever it’s worth.

 

[djevans]

Oh, on edit, it took three or four maybe five days more for the part to come in

 

[Ragin Rabbi]

Why were you in 4 wd on a paved road out of curiosity?

 

[GSPHerder]

At lower 1500 RPM where the Taco likes to live the torque converter isnt fully locked and will slip and cause overheating issues. I found that once i hit 2k rpm or higher the tranny temps drop and are stable. Higher RPM and manual shift mode is your friend.

 

[joebangle]

Why were you in 4 wd on a paved road out of curiosity?

The truck was in 2wd the entire time.

 

[joebangle]

Oh, on edit, it took three or four maybe five days more for the part to come in

Thank you for the insight. Did you have a Jerky 2-3 shift first thing in the morning? I still do and wonder if that sensor you mentioned is causing the overheating and the weird shifting possibly?

 

[joebangle]

At lower 1500 RPM where the Taco likes to live the torque converter isnt fully locked and will slip and cause overheating issues. I found that once i hit 2k rpm or higher the tranny temps drop and are stable. Higher RPM and manual shift mode is your friend.

So apparently these trucks are doing excessive data capture with how the truck is driven etc. You would think they would also be recording engine and transmission data as well? These vehicles are so electronic they even know the angle of the vehicle. Wouldn't they know to change the shift pattern to hold gears or lock up the converter if you are on an incline? Or even better if the transmission temps are rising wouldn't the computer tell it to lock up the converter to prevent excessive heat? Or is this just crazy talk for them to design something to do this?

 

[joebangle]

Keep in mind that with an automatic transmission, lower engine RPM will generally create more heat in the transmission when climbing grades. So lugging gears will cause more transmission slip and heat. On long grades, you are usually better off manually selecting a lower gear with a slightly higher engine RPM than taking it easy and lugging the engine and transmission. The higher engine RPM helps in two ways. It develops more transmission pressure and volume pushing through the cooler and the transmission is able to lockup instead of slip. The cooling fan is electric so the higher engine RPM will not increase airflow over the transmission oil cooler.

Good insight with the transmission temp. I sped up the rpm in park at the top to increase the volume of fluid going through the liquid to liquid transmission cooler. Because the engine wasn't overheating I assumed it would help cool the fluid off if that makes sense?

 

[djevans]

Thank you for the insight. Did you have a Jerky 2-3 shift first thing in the morning? I still do and wonder if that sensor you mentioned is causing the overheating and the weird shifting possibly?

The truck has always shifted "slightly" different, cold than when warm. But, after a couple of blocks of travel, I don't recall anything other than perfectly smooth shifting. That initial "cold" shifting definitely seems to me, transmission or TCM related. (not caused by the engine) When home, the Tacoma is always in a temperature controlled garage, and is never put in to any gear until after the initial engine warmup RPM drops down. (about 20 seconds) This is by far the best behaving truck I've even owned or driven. I "baby" this thing and never abuse it FWTMBW. (well, towing might be considered at least "demanding use." - Even then I try to be as gentle as possible I'm looking for 250K to 300K miles before anything major)

 

[Cappaworks]

I’m not sure of the plumbing of the Tacoma transmission and if that makes difference, but simply letting the vehicle idle in park is all you need to do to cool off the transmission fluid. There is no need to rev the engine in park.

 

[Ragin Rabbi]

The truck was in 2wd the entire time.

Sorry, must have misread it.

 

[Someguysomewhere26]

I have a whole forum explaining in more detail however super short explanation.

My transmission went out at 7000k

I had the overheating issues I did notice that switching to s and locking it at 2 or 3 depending helped with the heat off-road I have NOT gone on a trip since it’s been replaced.

I DID have the shift jerkiness after a cold start that COMPLETELY went away after being replaced.

So far anyways been a couple months and 2k miles


The trans overheating issues has been mostly thought to be the torque converter not locking up the way it’s supposed to so switching to s helps lock it.

Or they are bad time will tell hopefully we all find out more eventually but who knows

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