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Old 05-05-2021, 11:28 PM   #1
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Join Date: Aug 2019
Location: Auburn, WA
Posts: 651
Year: 2000
Coachwork: IC / Amtran
Chassis: 3000 / 33' Flat Nose
Engine: IC T444E / Allison MT643
Rated Cap: 72 Kids / 48 Adults
Aux oil and tranny cooler questions

I'm planning to add auxiliary oil and tranny coolers to my rear engine bus. The question is where to place them. Their placement also determines if I include fans on the coolers or not.


1) My research has alluded to, yet not specified, about the importance of flow and PSI when adding a cooler.

If anyone knows how to figure this out, please share.

2) The placement of the transmission cooler is suggested to be on the return line. This way the fluid is going back in already cooled.

The oil cooler uses an adapter that goes between the oil filter male port and the oil filter itself. The adapter also has the ports for the cooler lines.

3) Per the placement of the actual coolers. Attached our pictures of my radiator. I removed the back cover and measured the gap between the radiator and the back cover, which is 2.75".

I believe this is more than enough space to place the actual coolers. Included in the pictures show a channel, one on each side of the radiator, that provide great access to the oil filter and hopefully the transmission return line.

While they coolers would block about 4" of the radiator, they would be down low and not interfere with the intercooler, which I believe sits up high.

4) I researched the types of coolers and feel that the stacked plate coolers provide the highest cooling effect. If I do place them in front of the radiator, I won't use a fan. Otherwise I will use a fan.

5) I have not done any research on how to control the flow to the coolers. I'm sure there's some type of thermostatic valve? I'll research it, but any input is welcomed.

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Old 05-05-2021, 11:29 PM   #2
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Join Date: Aug 2019
Location: Auburn, WA
Posts: 651
Year: 2000
Coachwork: IC / Amtran
Chassis: 3000 / 33' Flat Nose
Engine: IC T444E / Allison MT643
Rated Cap: 72 Kids / 48 Adults
Ooops, forgot the pictures.
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File Type: jpg IMG_20210505_203628778.jpg (138.5 KB, 2 views)
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File Type: jpg IMG_20210505_203707481.jpg (151.7 KB, 2 views)
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Old 05-06-2021, 09:22 AM   #3
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Join Date: Nov 2014
Location: NM USA KD6WJG
Posts: 783
Year: 1991
Coachwork: Bluebird
Chassis: All American RE 40 FEET
Engine: Cummins 8.3
Rear engine buses have marginal radiator / air flow issues. Depending on where you live this becomes a larger problem. You live in the PNW and can get away with a lot of things I can’t. With that being said it is possible that you may go some place where it is hotter that the hinges of Hades. Good engineering practices will take that into account. The bottom water of the radiator cools the Allison and the engine oil. Adding an oil cooler in front of that will give off that heat from the auxiliary cooler to the radiator and to the rest of the system. By moving the cooler out of the radiators air stream all the heat removed by your new cooler helps your radiator capacity. Most of the hoses on the Allison MT 643 cooling are 100 R 5 spec. and use #12 JIC flare. This hose is in fact 5/8” hose. If you buy reusable hose ends and bulk hose you can make your own. Replace all the hoses. Flow from converter out fitting (top of transmission) to OEM oil to water cooler already installed then to auxiliary cooler then to filter and to the pan fitting. It is done this way in case anything happens with trash accumulating in the cooler circuit not getting back the transmission. Put a temp sender in the return line before the filter and you will be able to monitor better. Install a fan switch on the cooler in line to engage the fan on the auxiliary cooler set to 200-215. I used 215. It could have been 200 and would have worked better. My radiator is left side mounted freshly rodded out, new hydraulic fan motor and on 100 degree days with a hard wind coming from the right it was marginal on flat ground at 60-65 MPH. The auxiliary cooler dropped radiator bottom temperature about 5 degrees. I have a temperature gauge on the bottom of the radiator too. Your bottom temperature is your early warning devise for upcoming problems. Sorry for the long post but...
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Old 05-06-2021, 12:51 PM   #4
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Join Date: Aug 2019
Location: Auburn, WA
Posts: 651
Year: 2000
Coachwork: IC / Amtran
Chassis: 3000 / 33' Flat Nose
Engine: IC T444E / Allison MT643
Rated Cap: 72 Kids / 48 Adults
S2, excellent post! Thank you!

I have a space above the radiator that will not block the OEM coolers. I'll measure that area and see what aux coolers are available to fit in there.

I'm still concerned about oil and transmission pressures and flow being affected by the addition of the aux coolers.

Should I simply get a cooler that has equal to or larger than ID pipe/hose to assure the pressure and flow are good?

How does additional fluid and distance that fluid travels affect the OEM oil and tranny pumps?

I'm really trying not to screw this up and 1) waste money on coolers, piping and fittings, 2) wreck my engine / tranny.

Ignorance sucks!
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Old 05-06-2021, 01:31 PM   #5
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Join Date: Nov 2014
Location: NM USA KD6WJG
Posts: 783
Year: 1991
Coachwork: Bluebird
Chassis: All American RE 40 FEET
Engine: Cummins 8.3
RE buses have shorter transmission cooler lines than FE buses so I don’t think the added length is going to amount anything. It is the elbows and tees and the like that can be problems. If you use gradual bends, in the end your filter will be your biggest restriction. It will not hurt to oversize the cooler to #16 or 1 inch fittings on the cooler to lower restriction. 2 pressure gauges teed into the start and end of the system will tell you every thing you need to know. But I don’t think it will be needed. I changed my filter to one of the newer higher flow Allison filters used on the larger transmissions. These systems are not marginally engineered.
And by the way, ignorance is just an inconvenience. Stupidity sucks.
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