Trans coolers

220 for modern ATF synthetics is not hot at all. Warm, but not hot.

The warning chime for my truck comes on around 265 or 270?

You can put another cooler on as you have said but there really is no reason too. The problem also it if you do cool off the tranny then those BTU's will go into the engine coolant stack and that can cause problems too.

Not saying to not put another ATF cooler in the stack, I'm just telling you some of the drawbacks because very few on this site seems to want to talk about those.

220F is the upper limit but not excessive IMO when going up a grade with a trailer.

As long as it cools down again when you are not working it hard, then your current cooler is doing it's job.

Your trans probably has an internal thermostat on it anyway.. So, it'll only cool down so much anyway.. Probably around *190-195 range.

If you do decide to get more cooling for the trans, don't add a second cooler... Get a bigger cooler than OEM and leave it all plumbed the same way.

Good luck! Mitch

I like to see trans temperature reach 220 occasionally. Water condenses in the trans oil and needs to be boiled out occasionally.

I like to see trans temperature reach 220 occasionally. Water condenses in the trans oil and needs to be boiled out occasionally.

Roger10378 wrote:
I like to see trans temperature reach 220 occasionally. Water condenses in the trans oil and needs to be boiled out occasionally.

I like your theory, but in 30+ years of driving and exclusively wrenching on all my own stuff and some for others, I have never come across that issue in any vehicle new or old save for maybe one that was severely neglected.
And if it was even remotely an issue, I don’t believe most auto trans mfgs would design them where they ideally Never reach anywhere near that high of oil temperature.

8 miles at 8% under a load will clean the cobwebs out of most vehicles.
What temps do you run, say on a 4-6% at highway speeds?
Also, 3000rpms is nothing for a LS motor. If you dropped it another gear, the trans would run a bit cooler.
Now if you’re pulling steep grades frequently which you may be, presume a 6 speed suburban has an external cooler, I’d consider a larger cooler. Or another option, deep pan for more fluid capacity and a bit of cooling with a finned pan may yield similar results.

Ideal operating temps for modern Automatic Transmissions are from 170F - 225F.

I wouldn't worry about 220F for a short time, especially when climbing a steep grade where temps tend to rise when pulling hard.

One important step when towing is to change fluids more often. Every fluid, engine oil, Atf, Engine Coolant, and Power Steering fluid take a beating under the heat created by towing.

On my vehicle I change Oil every 5K and ATF/PS/Coolant every 50k. So far my 19 year old truck (2004 Titan) tows my 6,000 trailer up anything I've encountered in the West.

If I were towing with a V8 going up grades in the mountains I shift down to keep the rpm's up. This results in more HP and lower tranny temps. Your V8 probably puts out just over 200 HP at 3000 rpm's. Kick it down, rev it up a bit and you are making close to 400 HP and will top grades at whatever speed you want and the tranny will be cooler.

A couple things to note re: McDonald Pass. Average grade is just under 6% but there is one significant stretch that's 10%.

If the OP is "doing OK" most of the time I'd just gear down and keep moving if back on that road again.