Preparing for a long trip and then...high trans temps...

Hey everyone. Hope your 4th of July weekend is going well.

I'm preparing for a long trip across the country and had some alarming trans temps today. Was stuck in traffic in the mountains today (was about 95 out) and my trans reached 220. First time I've ever seen a number like that. Was dead stop and then stop and go traffic up a pretty steep hill with no way off the road unfortunately. Had temps around 210-220 on and off for about an hour.

I'm running a Koyorad and a B&M 70268. I recently did a trans drain and fill and filter replacement (at 300k, which was 2k miles ago). The majority of my driving since the drain and fill has been 100 above outdoor temp. If I'm going through mountains I turn off O/D and I rarely see above 200 even on super hot days.

I'm about to take a pretty long road trip (around 3k miles) with multiple people and lots of gear in my truck and I'm afraid when I'm going through Utah / Colorado I could see numbers peak like this and do more damage to the trans. I haven't experienced any slipping or codes or anything.
Wondering what my best options are here / what you folks would suggest as my next move. My thought is to get a cooler that has a fan I can control or run a second cooler.

220 is getting to the higher end of normal operating temperature for ATF. If you start to see 250 or higher, that's when you're getting into the temp that will start to cook the fluid.
If it was me, I wouldn't worry about a new cooler or fan until you have a 250 degree issue. You were in stop and got traffic in mountains on a hot day, which will put a high load with little airflow over the cooler

How the filter looking? If the screen filter is plugging your fluid volume will decrease causing a fluid temperature increases..

Any change with over drive off or the transmission in ECT pwr mode?

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Thermostat DELETE


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DenverAirport said:

Hey everyone. Hope your 4th of July weekend is going well.

I'm preparing for a long trip across the country and had some alarming trans temps today. Was stuck in traffic in the mountains today (was about 95 out) and my trans reached 220. First time I've ever seen a number like that. Was dead stop and then stop and go traffic up a pretty steep hill with no way off the road unfortunately. Had temps around 210-220 on and off for about an hour.

I'm running a Koyorad and a B&M 70268. I recently did a trans drain and fill and filter replacement (at 300k, which was 2k miles ago). The majority of my driving since the drain and fill has been 100 above outdoor temp. If I'm going through mountains I turn off O/D and I rarely see above 200 even on super hot days.

I'm about to take a pretty long road trip (around 3k miles) with multiple people and lots of gear in my truck and I'm afraid when I'm going through Utah / Colorado I could see numbers peak like this and do more damage to the trans. I haven't experienced any slipping or codes or anything.
Wondering what my best options are here / what you folks would suggest as my next move. My thought is to get a cooler that has a fan I can control or run a second cooler.

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You are doing the right things.You need to know the AT pump is moving oil fast enough thru the cooler and the radiator(an obstruction? I did all the same things and put in a high capacity cooler and New Denso radiator recommended by Timmy as well as a magnefine filter which can restrict flow if obstructed. I use synthetic fluid and never see temps above 175-180 even pulling high long mountain passes on a warm day. I wonder if your tranny is slipping and generating heat. I had a bad torque converter in my Cummins dodge and had temps spike to 240 towing in the hills. Once fixed the temps dropped to max 180. Something is wrong.

Stop and go traffic - no air flow. Your torque converter is in a constant state of slipping as it's never able to reach 3rd/OD and lock up so it creates a lot of heat. No cooler is going to help under those conditions. Put it in Lo and creep along

You mentioned B&M 70268, are you bypassing the radiator or is the trans cooler inline? If you're bypassing, it may not be sufficient to cool the trans at those ambient temps. Since you serviced the transmission recently, I want to say that's suspect, but I don't know where I would start, aside from opening it back up and see if all looks well? Like others said, logically, 220 is within bounds, logically, but it's different when it's YOUR truck and you have a big trip coming up... Keep us posted and good luck!

brillo_76 said:

How the filter looking? If the screen filter is plugging your fluid volume will decrease causing a fluid temperature increases..

Any change with over drive off or the transmission in ECT pwr mode?

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No change with O/D or ECT but like others have said, it was just the driving condition I was in.

Hopeless Diamond said:

Stop and go traffic - no air flow. Your torque converter is in a constant state of slipping as it's never able to reach 3rd/OD and lock up so it creates a lot of heat. No cooler is going to help under those conditions. Put it in Lo and creep along

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I should have put it in Lo. Good point. This seems to be the reality of the situation I was in and I'm overthinking it a bit.

DK327 said:

You mentioned B&M 70268, are you bypassing the radiator or is the trans cooler inline? If you're bypassing, it may not be sufficient to cool the trans at those ambient temps. Since you serviced the transmission recently, I want to say that's suspect, but I don't know where I would start, aside from opening it back up and see if all looks well? Like others said, logically, 220 is within bounds, logically, but it's different when it's YOUR truck and you have a big trip coming up... Keep us posted and good luck!

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Responding to this because I think it's important for search results but the aluminum Koyo doesn't have a trans cooler so I'm just using the 70268.

Just took a 3 hour trip today as a "warm up" and drove on some mountain roads and never saw above 200. Was around 180-185 the whole time and was 90 degrees out so I'm feeling good for now!

DenverAirport said:

Responding to this because I think it's important for search results but the aluminum Koyo doesn't have a trans cooler so I'm just using the 70268.

Just took a 3 hour trip today as a "warm up" and drove on some mountain roads and never saw above 200. Was around 180-185 the whole time and was 90 degrees out so I'm feeling good for now!

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Air flow over that cooler really makes the difference. When you're not moving very fast (under 30 MPH or so) it's not enough airflow over the cooler to really cool it down. Good job installing a cooler in the first place as that pretty much guarantees that it will not overheat. Drive confidently.

DenverAirport said:

No change with O/D or ECT but like others have said, it was just the driving condition I was in.

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When was the last time the external screen transmission was changed?
Clean filters lower transmission fluid in driving conditions. As the volume of fluid drops when the filter plugs. Just a thought if Temps keep going up under certain conditions.



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brillo_76 said:

When was the last time the external screen transmission was changed?
Clean filters lower transmission fluid in driving conditions. As the volume of fluid drops when the filter plugs. Just a thought if Temps keep going up under certain conditions.



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Oh sorry if I ignored this question earlier, I had it in the post. Put in a new filter 2k miles ago when I did a drain and fill.

I will say that today I experienced some shuddering while backing up and end of day got a P0770 code so not looking good. I've noticed my trans to bit a bit louder than usual over the last 10k miles which is why I made sure to get a drain and fill at 300k. Still no whining or significant slipping.

The last 30 miles of my day today made me a lot less confident about my trip.

gamefreakgc said:

Air flow over that cooler really makes the difference. When you're not moving very fast (under 30 MPH or so)...

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+2, an electric fan, manual or otherwise really makes a diff in those situations which is like crawling under 5mph, the roughest cooling wise. Helps A/C too.
Airflow is King.

Pop it in neutral when you're at a red light. That will take the load off your transmission and let your engine idle a little higher, which will spin your fan faster = cooler temps.

DenverAirport said:

I will say that today I experienced some shuddering while backing up and end of day got a P0770 code so not looking good. I've noticed my trans to bit a bit louder than usual over the last 10k miles which is why I made sure to get a drain and fill at 300k. Still no whining or significant slipping.

The last 30 miles of my day today made me a lot less confident about my trip.

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Ok, that changes things a bit. If your torque converter is not locking up then you will definitely see higher than usual temperatures. There's a driving test you can do to see if the torque converter is locking up correctly.

1. Drive around a bit until the fluid temperature starts to rise. Normally that's about 2-3 minutes of driving.
2. On a flat road that allows slow acceleration to over 50 MPH, drive from a stop and slowly increase your speed.
3. Count the number of shifts. We have a 4-speed auto with torque converter lockup so there should be 3 gear shifts and then a 4th 'shift' at 50 MPH when the torque converter locks up under light throttle. If you are under moderate or heavy throttle it will not lock up. It will also never lock up and shift below 50 MPH on stock tires and gears. Please adjust as necessary for larger tires or shorter gears.

You should be able to count the number of shifts to 4. Also once the torque converter is locked up and you apply a little bit more throttle the RPM remains flat and only increases with speed. If the torque converter is stuck in the unlocked position the RPM's will rise but speed will not rise immediately.

If the torque converter locks up as expected then the shift solenoid E needs to be replaced as it may be faulty. However the shuddering when backing up is a bad sign and there may be damage to the torque converter itself. My torque converter and planetary gears failed in my transmission last year. Some of the signs I had was increased noise as it started to whirr and then it felt like the 4Runner had dragging brakes or driving through mud. Started taking more and more throttle to keep the same speeds. It never threw a code though which means there might be hope for yours as it did throw the torque converter solenoid code.

DenverAirport said:

Oh sorry if I ignored this question earlier, I had it in the post. Put in a new filter 2k miles ago when I did a drain and fill.

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My bad.. Sometimes i loose track. at 2K its a non issue.

2021nightshade4x4 said:

Thermostat DELETE


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Not exactly sure what pulling the thermostat is going to do with transmission temps? However, ok..

Without a radiator cooler in series.. I could see temps creeping while setting still.

This video helps explain the Torque convertor.
THIS Is the Most Underrated Car Invention in 2023 | The Torque Converter - YouTube

So we have 300K on a transmission and its getting hot. The TC is probably getting got warm a few times and might have the lock up section warped slightly.

If its starting to whine, quiet in natural and seems to need more beans to get it moving. The TC maybe on its way out. :-(

That's a gamble, as if the TC is bad, its possible the Transmission is going too..:-(