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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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!

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

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.

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!

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.

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.

+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.