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turf 07-10-2016 05:06 PM

adding a transmission cooler to my AT545
howdy folks,
i've been bitching about my transmission on other threads so i finally did something about it. i'm adding a transmission cooler.

i found a used transmission cooler on the internet and ordered it. here is the picture off the internet.

it came a day or 2 later and i still needed to disassemble a few parts from it.

i want to mount this under the front passenger seat of the bus, right next to the transmission heat exchanger.

this is peaking in front of the front passenger tire on the flat nose bus. where the cooler is going to go:

and here it is with the bracket made for the frame rail:

and now the bracket for the outside.

that cooler is hanging solid!!!!

gonna take a few days to get it plumbed and wired. its good to have friends that fabricate for a living. i can weld, but visualizing what needs to be there takes some experience.

Elliot Naess 07-10-2016 06:14 PM

An extra cooler can't hurt -- so long as you plumb it correctly. You want the new cooler between the transmission and the original cooler that interacts with the engine water.

Reason is that the transmission needs to get up to a certain minimum temperature also. The original cooler brings it up to operating temperature by heating the transmission fluid as soon as the engine warms up. And in cold weather, the extra cooler could over-cool the fluid.
So the engine-water transmission cooler should always be the last cooler in the transmission's cooling circuit.

Another thing while I'm here, and this applies to any bus. We covered this in an other thread a little while ago, but....

When I installed a manual switch on Millicent's engine fan (bypassing the thermostatic switch on demand), I discovered that running the engine fan had a major cooling effect on the transmission -- even though the engine water temperature gauge did not move.

This is because the thermostat regulates the temperature in the engine. But what the transmission sees... is the water coming out of the bottom of the radiator.

turf 07-10-2016 06:35 PM

hmmmm very interesting......

my only source of info is a youtube video but they stated the opposite. i was planning on it down line from the (i'll call it the) heat exchanger, right before the transfilter on the return line of the cooler.

their rational was that if the engine is hot ~ 220ish, the heat exchanger wasnt enough cooling for the transmission.

perhaps the cooler doesnt work well without the fan running on it? its got a fan and thermostat. not sure how im gonna plumb it now.

the cooler's purpose is for my summer climbs into the rockies. not much winter use for the bus.

On a different note.... the transmission was marked as a Allison AT545RE. is that RE "retarder" how do i make that work?

thanks for all the help

turf 07-19-2016 03:22 PM

i finally got the parts and hoses to get the cooler plumbed today. it comes out of the heat exchanger and into the cooler. plumbed into the return line back to the filter and transmission.
3 qts of fluid got me to full after running the engine a bit. i took it on a test drive and no leaks, shifts fine. engine temp gauge never quite got to 190 on a real hot day.
i still have a fan to add, but liking all so far.

Booyah45828 07-19-2016 05:04 PM


Originally Posted by Elliot Naess (Post 154921)
An extra cooler can't hurt -- so long as you plumb it correctly. You want the new cooler between the transmission and the original cooler that interacts with the engine water.

I also think this is how it should be done. The water to oil cooler will do more for cooling then the air to oil one will, so long as your cooling system is functional.

If you notice, the water sourced for the cooler is at the bottom of the radiator which won't be 220. It should be substantially less(<140 or even less would be better)
I see it often where people will eliminate the cooler from the radiator and replace it with a big finned job in front of the radiator and end up puking all the trans fluid out of it. I've seen it in cars, pickups, and motorhomes.

Not sure if I'm reading this right, does your cooler have a thermostat bypass on it? If it does, you shouldn't have to worry about warmup in the winter, but it sounds like your not too worried about that to begin with.

turf 07-19-2016 05:42 PM

there is no bypass that i put in. its all in line.
i believe that i tapped into the return line of the trans cooler, post cooler.

after Elliot's comment, i looked a lot online and every source i found says to put an aftermarket transmission cooler after the vehicle's own cooler. i respect your's and elliots wisdom more than most peoples, i just could find nothing to confirm that installation.

does the transmission have an internal thermostat and fluid pump, or does the the pump always circulate trans fluid?

i think changing the order of coolers would only be a matter of moving the hose from the bottom of the heat exchanger to the top of it. how cold is too cold for the fluid?

i have been abusively towing with the 545 and after the last trip over a 10,000 ft pass, feel lucky it still runs. im going to give this set up a run for a bit, probably change fluids in a few hundred miles.

Carytowncat 07-19-2016 08:52 PM

i'll be darned i always wondered why the old GMC truck had the trans fluid cooling through the radiator. Never knew it needed a little warmth and a little coolz.
kinda like Goldilocks; looking for a temp that"s ahhhh just right. :)

jazty 07-20-2016 11:12 AM


Originally Posted by Elliot Naess (Post 154921)
An extra cooler can't hurt -- so long as you plumb it correctly. You want the new cooler between the transmission and the original cooler that interacts with the engine water.

I haven't looked into it much for larger vehicles, but the discussions I was reading last fall on adding transmission coolers to Subarus seem to agree. You don't want the transmission running cold, but you don't want it running too hot either.

It seems there are a few different configurations that will provide a consistent operating temperature.

- A separate radiator for the transmission fluid with a thermostat and a bypass.
- Using the stock transmission cooler/heater that is built into the radiator and a separate radiator for transmission fluid. The Subaru experts strongly recommend putting the standalone radiator first to super cool the trans fluid, then bring the fluid to the stock cooler/heater to make sure it is up to normal operating temperature. The stock heat exchange on the Subarus is on the colder side of radiator.
- And a couple other more complicated ways :)
^ That post has real nice diagrams, by the way

In a moderate climate it probably doesn't matter much either way. With the cold winters we have up here I would be running it through the stock cooler/heater before heading back to the transmission.

turf 07-20-2016 01:13 PM

thanks for the info.

i promised myself i wouldnt drive the bus in snow. however, i can see a cold weather problem, potentially, but that is not when this bus is driven. i try to tow my atv up and down the Rockies during the summer as many times as i can. its a summer use rv, when it freezes it sits.

i could return it to stock in a few minutes for winter driving if needed.

i need to take the bus on a test run and check temps. the bus only has the water temp gauge, but i'll find a thermometer to check the cooler and radiator.

here the cooler installed, just peeking out in front of the front tire.

turf 07-23-2016 11:35 AM

i took the bus out for a test run yesterday, maybe put 50-60 miles on it with just the cooler hooked up. no electric fans yet.

the bus ran great!!! on the interstate i hit 70 a couple of times which is real rare. before i thought my top speed was ~67mph, but i gained a bit of power/speed with the cooler transmission.
temps this week and last are right around 100f everyday, and the truck was running good and cool. the truck did get hot enough to kick the fan clutch in once, but overall, it was running cooler than expected.

this morning, i finish up the install of the cooler by adding 2 fans to the cooling system. one fan pulls air through the cooler, and the other fan i just mounted to the front of the intercooler to blow air when temps get up there.
i also wired the fans through a relay so that i can have them run off of a thermostat or i can turn them on manually in the cab with a button on the driver's control panel.

here's the fan one the trans cooler:

here's the new fan on the bus:

i got the fans from JEGS, they were cheap enough that i got 2 to make sure i got the right size. i knew i'd find a use for fan #2.

if i was gonna redo this, i see in the JEGS catalog, the have some nice coolers from Derale called "hyper cooler remote cooler", i'd probably start with that instead of what i did.
i'm done with the cooling system, gona see how this runs for a bit, probably update if i change fluids.

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