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Old 07-24-2020, 10:04 PM   #1
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Tranny temp, what’s yours?

I have an Allison Md3060 that seems to run cool. Too cool??
My maiden voyage in June 2018 from Ohio-Alaska tranny temp was steady at about 130-140* Fahrenheit. This was running 60+mph ALL day (limited to 5 gears). I saw 180* once In some hard Canadian mountain passes and once running the PTO-driven 25kw generator. Here in Alaska it is driven almost daily April-October and the tranny rarely gets much over 100*. Most trips are less than an hour, but it’s not unusual to drive 60 miles at 65-70 (now that I have 6th gear unlocked😃). Ambient temps here are typically 50-70 Fahrenheit in the summer, though 2019 we saw 80-90 (heat wave!😄). The truck weighed 19k pounds coming up, and about 23k as currently loaded.

Up to about a year ago I assumed this low temp was normal (and panicked a bit on the 180* occasions). Bit most people have mentioned 180-200* as their “normal”.

Heat kills our trannies, but Any problems associated with cool tranny temps?

Also, It’s time to see if anyone else has a similar experience. If this is unique to me then either my gauges are lying or SOMETHING is funky.

What is your “NORMAL” tranny temp? What are common “WARM” or “HIGH” temps that you see.

If known, please mention your transmission model. Vehicle weight and driving conditions are helpful too.

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Old 07-25-2020, 12:16 AM   #2
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Quote:
Originally Posted by concrete View Post
I have an Allison Md3060 that seems to run cool. Too cool??
My maiden voyage in June 2018 from Ohio-Alaska tranny temp was steady at about 130-140* Fahrenheit. This was running 60+mph ALL day (limited to 5 gears). I saw 180* once In some hard Canadian mountain passes and once running the PTO-driven 25kw generator. Here in Alaska it is driven almost daily April-October and the tranny rarely gets much over 100*. Most trips are less than an hour, but it’s not unusual to drive 60 miles at 65-70 (now that I have 6th gear unlocked��). Ambient temps here are typically 50-70 Fahrenheit in the summer, though 2019 we saw 80-90 (heat wave!��). The truck weighed 19k pounds coming up, and about 23k as currently loaded.

Up to about a year ago I assumed this low temp was normal (and panicked a bit on the 180* occasions). Bit most people have mentioned 180-200* as their “normal”.

Heat kills our trannies, but Any problems associated with cool tranny temps?

Also, It’s time to see if anyone else has a similar experience. If this is unique to me then either my gauges are lying or SOMETHING is funky.

What is your “NORMAL” tranny temp? What are common “WARM” or “HIGH” temps that you see.

If known, please mention your transmission model. Vehicle weight and driving conditions are helpful too.

Good question, I don't have an answer for you but I'm curious to learn what the answer is.


edit: I like your truck, BTW. Ex medium duty ambulance?
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Old 07-25-2020, 01:47 AM   #3
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Thanks!
My truck is a ‘95 IH 4900/fire department Heavy Rescue. I bought it from the fire department in Wooster Ohio. Only had 34k miles on it two years ago! They took great care of the ole beast! After seeing how some departments “retire” their equipment I’m very happy to have purchased from them.
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Old 07-25-2020, 08:41 AM   #4
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The hottest I've ever seen mine go to is around 200°F, but that was when it was 90+°F ambient doing 70 mph on the interstate with coolant and oil temps around 230°F.

I don't see a situation where I could have gotten it hotter then that. So I'm fine with where it was running.

My trans is the AT545, and my trans temp gauge is an electric unit from autometer with the probe placed in the outlet of the transmission(post converter) going to the cooler. Theoretically, that should be the hottest part of the fluid chain aside from localised hot spots inside the torque converter itself.

The heat your trans can take depends on the trans and the fluid you're using. If it's an older trans with high mileage and conventional atf, you need to baby it more then a modern trans with synthetic fluid.

I'm not sure if I'd say there is a minimum temp that your trans should operate at. Ideally you want it hot enough that moisture in the fluid boils off, but the only source of moisture in the transmission is from condensation, so it's minimal. Most fluids can operate over a broad temp range, especially synthetics, so I wouldn't be all that concerned of minimum temps.

Your temps of 140 while cruising seems fine/normal. Mine will run around 150 doing 55mph all day long.
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Old 07-25-2020, 10:11 AM   #5
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i run on the cool side.

i added a trans cooler and now i have a hard time getting my trans up to 180. they sell a temperature bypass valve you can install on the cooler lines to help you get up to temp but i havent gone done that rabbit hole yet.

prior to the cooler, mild hills would smoke my trans fluid so.... this is better than the prior solution. im easily 20k miles on the cooler setup. no issues yet.

if you are in Alaska, you may need to add the bypass for winter driving.

good luck
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Old 07-25-2020, 12:17 PM   #6
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Originally Posted by Booyah45828 View Post
The hottest I've ever seen mine go to is around 200°F, but that was when it was 90+°F ambient doing 70 mph on the interstate with coolant and oil temps around 230°F. My trans is the AT545, and my trans temp gauge is an electric unit from autometer with the probe placed in the outlet of the transmission(post converter) going to the cooler. Theoretically, that should be the hottest part of the fluid chain aside from localised hot spots inside the torque converter itself.
Mine will run around 150 doing 55mph all day long.
Thanks Booyah. I’ve heard of scary temps with the at545, but yours sounds like a very healthy setup. Did you do anything with your system to control the temps (other than the auto meter gauge)? And any idea of the weight of your rig?
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Old 07-25-2020, 12:26 PM   #7
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Originally Posted by turf View Post
i run on the cool side.

i added a trans cooler and now i have a hard time getting my trans up to 180. they sell a temperature bypass valve you can install on the cooler lines to help you get up to temp but i havent gone done that rabbit hole yet.

prior to the cooler, mild hills would smoke my trans fluid so.... this is better than the prior solution. im easily 20k miles on the cooler setup. no issues yet.

good luck
Thanks Turf.
Did you get your cooler from the local parts store or was it a special order?- I ask because they are not all created equal and it sounds like yours solved a real problem.
And any info on which tranny and bus weight?
Thanks again for posting!
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Old 07-25-2020, 01:39 PM   #8
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Quote:
Originally Posted by concrete View Post
Thanks Booyah. I’ve heard of scary temps with the at545, but yours sounds like a very healthy setup. Did you do anything with your system to control the temps (other than the auto meter gauge)? And any idea of the weight of your rig?
I have too.

I've got my theories on why some do, and why mine doesn't.

My engine operates a few hundred rpm higher then most diesel engines, so there is less torque converter slippage in my setup. I also have a properly adjusted modulator cable, which is a big thing to preventing trans slippage. My fluid is clean, filter is new, radiator clean, etc.

Essentially, my system is working like it's supposed to, which is why the temps are normal. I've done nothing additional, no extra coolers or anything like that.

Yes, the AT545 has it's flaws, and isn't the best trans option out there. But most failures can be attributed to either a lack of maintenance or wear. Transmissions do have a life span, and when they reach the end of that repair or replacement is required.

Oh, and I have no idea on bus weight. Maybe 15k lbs? It's a full sized bus that has a simple conversion, so it isn't necessarily light or heavy either.
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Old 07-26-2020, 12:26 PM   #9
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I ran across a thread in another RV forum discussing this subject. Mostly 3000 series Allison 6 speeds from the early 2k years. Temps varies a lot. Some averaged 135-145*, others 10-30* above engine temp, others the same below. Various theories propounded, but nothing definitive. That forum is more silver spoon��, less hands on/diy, which is why I concentrate my questions here��.
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