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Old 08-19-2021, 08:43 AM   #1
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External Allison Transmission Cooler Setup

I decided that I wanted to eliminate the factory transmission cooler (which uses engine coolant to cool the transmission) and make an independent setup on my 2000 HR Endeavor (Cat 3126 engine, Allison 3000 transmission, Freightliner XC chassis).

For this, I used two Derale 15875 coolers. This was overkill, but the transmission now cools great and my engine runs cooler. It wasn't a cheap modification to do, but it's cheaper than a new transmission or a blown head gasket. Plus, I long term want to convert the engine to electric cooling fans so this helps to divorce the transmission from the main cooling system, making that easier to accomplish. [Mod Edit]
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Old 08-19-2021, 08:45 AM   #2
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A good idea for operating in 90 degree plus conditions.


Be aware that you can OVER-cool transmission fluid as well as have it too hot.


If driving in sub-freezing temperatures, would see if you can make a cover to block off air flow to the new cooler.
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Old 08-19-2021, 09:02 AM   #3
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Interesting stuff, good video, and a nice explanation of the system. On the thermostatically controlled valve, does it just stop flow at 165 or does it by-pass and return the fluid to the trans? Or is that necessary? Also does engine heat serve to help warm up the trans and if so does it matter that you eliminated that function?

Moving on, when will you install the transmission retarder? Id like to see that video. I spent a lot of time researching this and trying to find someone willing to do the work, but it seems like an unpopular idea, even though it should be relatively simple, and not cause any issues other than creating some extra heat in the trans, which you’ve just addressed.
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Old 08-19-2021, 09:07 AM   #4
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Originally Posted by R.Wold View Post
Moving on, when will you install the transmission retarder? Id like to see that video. I spent a lot of time researching this and trying to find someone willing to do the work, but it seems like an unpopular idea, even though it should be relatively simple, and not cause any issues other than creating some extra heat in the trans, which youíve just addressed.

I am extremely familiar with Allison transmission retarders from my years with Foretravels.


I am not a fan of them IF your engine brake can control speed of descent on those grades.



Turning momentum into HEAT in the transmission vs an effective exhaust brake (like the PacBrake PRXB) or engine compression brake would not be something I would recommend-- even if the cost of the retarder is minimal (and it isn't).
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Old 08-19-2021, 09:22 AM   #5
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Quote:
Originally Posted by wolfe10 View Post
I am extremely familiar with Allison transmission retarders from my years with Foretravels.


I am not a fan of them IF your engine brake can control speed of descent on those grades.



Turning momentum into HEAT in the transmission vs an effective exhaust brake (like the PacBrake PRXB) or engine compression brake would not be something I would recommend-- even if the cost of the retarder is minimal (and it isn't).
Well that’s the thing - I have a VGT engine brake, which on a 6.7 provides only moderate engine braking (I give it a C-) and you can’t run an exhaust brake with it. If I had a 3-stage jake it wouldn’t be an issue.

A little extra trans cooling would take care of the heat issue and having operated fire apparatus with retarders for decades, I both understand them well enough to stay out of trouble, and miss having that assistance on grades. I’d pretty much given up on the idea until I saw Ted’s video - now I’m getting cranked up on the idea again.

Cost would be $4000-$6000 depending on parts sourcing and how much I do myself, and brakes are a lot cheaper, but as a safety measure it would be an added benefit. A little pricey but having added active air, it’s within my new price threshold for mods.

Back on topic:

Ted I have another question: is this placing more load on the fluid pump(s) in the trans and possibly reducing fluid pressure? Also how much did you increase your fluid capacity? That seems like another benefit.
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Old 08-19-2021, 12:42 PM   #6
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Some good questions and points.

Brett, you're correct that it's possible to overcool the transmission. This is definitely something I have thought about and am concerned regarding. Most of our driving has been in the summer/warmer temps. However, cooler temps and overcooling concerns were part of the reason I mounted the coolers horizontally. This way, the natural cooling is minimal and it more relies on forced air cooling, and thus I am not expecting it to overcool. We'll see if that works out or not, but yes, I figure if it presents some issues I can always block off one of the coolers.

R.Wold, what I have is a thermostatic switch that controls the fans, it doesn't control fluid flow. The fluid is always flowing, and then it turns on the fans when it detects 180F (on) down to 165F (off). I have considered adding a thermostatic valve that would actually bypass transmission fluid flow if I have overcooling issues, but I'll first see how things go as the temps drop.

To your other questions (out of order), I'm not certain exactly how much fluid I gained. I didn't track how much fluid came out, and I ended up adding 6 quarts to get it back to the computer telling me "OK." As far as the extra load on the pump, this is the biggest reason why I did the two coolers in parallel. I ended up buying the coolers I did (which have -10 AN ports) for two reasons. First, The fitting with a built-in fitting for thermostatic switch I bought only went up to -10 size, and two I found a good Amazon Warehouse deal on the -10 sized cooler. So two in parallel means I run -12 hoses from the transmission to the coolers (same as factory) and then just T them off and do reducers to -10 from -12 at the coolers. Additionally, these coolers are "rated" (per Derale) up to 30k lbs, which is pretty close to what I run. Knowing that I would mount it horizontally and thus not have any help on cooling from natural airflow, I figured this would make sure this would work. If you wanted to save some money and do another option (like a manual switch or something else machined for the thermostatic switch) you could do the -12 version of this cooler and I suspect it would be fine. You don't want to run the fan 100% of the time due to the overcooling concerns Brett mentioned above.

The transmission behaves well so I am feeling pretty confident I haven't hurt anything.

As to the retarder question, that's an interesting one. If you have some documentation I'd be interested in looking at it. On the 3126B (which is a 7.2L engine) I have an exhaust brake which I replaced last year and it does work. The engine braking between the transmission's automatic downshift function and the exhaust brake is decent. That said, on the Teton Pass (which is extreme at a 10% grade) I was in first gear, torque converter locked, exhaust brake on, and even then I had to use the service brakes some to keep it slowed down, which I wasn't super happy about. Since I am planning on eliminating the mechanical fan in favor of electric fans, that will be reducing the inherent engine drag and thus hurt my engine braking. I really wish I had proper Jake brakes on this thing, but they were never available on the 3126/C7 series, and a C15 won't fit (although I think a C9 would... which also doesn't have Jakes but does have more displacement and thus would have better exhaust braking).

Again, I'd be interested in seeing what documentation you found as it could be a worthwhile safety upgrade. I really like being able to stop my bus. I'll also be honest that for $4-6k that's probably outside of what I'm willing to spend on the mod, unless the OEM or some other sponsor wants to give me a discount on parts to sponsor a video (I've done this before on my Harley upgrade, and on the diesel engine swap I'm doing on my Land Rover Discovery).

Oh, and if you're interested in other interesting stability upgrades (like your Active Air), I'm going to be welding up some mounts to the rear suspension to use my old front anti-roll bar on the rear - my Freightliner XC didn't come with a rear bar at all, and I think this will help a lot.
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Old 09-07-2021, 03:20 PM   #7
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Before my trip this weekend, I tried insulating the hot side transmission cooler lines as well as putting insulation around the thermostatic switch. The hope was that this way the thermostatic switch would see the actual temperature of the fluid, rather than getting cooled by the surrounding air.

Before, at low speeds the fans were coming on at 185-190F, and at high speeds it was going on at 200-205F. Now, it's consistently coming on at 186-188F and off at 170-175F. Perfect temperatures. Works great. I am still very happy with this upgrade.
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Old 10-18-2021, 01:18 PM   #8
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As an engineer after thinking up an idea, and checking total cost, not prices, I add in opps. (Very scientifically). Then I actually justify on a return on investment basis.
I found in almost every case if a project isn't real inexpensive it just won't FLY.
Example Only: a K&N filter usually a $30-50 part won't pay for itself even in 25-50k miles, by given me .1 - .3 more mpg. But then I don't have to service or replace as often. And what are the long term effects. I've killed many many not well thought out ideas.
Can you really justify pending thousands?
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Old 10-18-2021, 02:40 PM   #9
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For the trans cooler or retarder? Iíll tell you from that perspective I definitely could not have justified $9,999.83 for Active Air, but it makes driving so much more pleasant, not to mention more safe. But cost effective? Probably not. Just a nice upgrade and slightly more useful and practical than an expensive watch or a short luxury cruise.

The retarder pretty much fits this category as well. A vaguely tangible safety enhancement, somewhat less brake wear, but primarily just more enjoyable and easier to drive. Essentially just finishing the coach to the standard at which it should have been built. IMHO...

The coach is also worth about $30k more than I paid for it, so that rather ensures that I wont lose on these little projects short term should I tire of the thing and sell it. But thats not likely with all these spiffy upgrades.
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Old 10-20-2021, 05:12 AM   #10
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Quote:
Originally Posted by Fiesta48 View Post
As an engineer after thinking up an idea, and checking total cost, not prices, I add in opps. (Very scientifically). Then I actually justify on a return on investment basis.
I found in almost every case if a project isn't real inexpensive it just won't FLY.
Example Only: a K&N filter usually a $30-50 part won't pay for itself even in 25-50k miles, by given me .1 - .3 more mpg. But then I don't have to service or replace as often. And what are the long term effects. I've killed many many not well thought out ideas.
Can you really justify pending thousands?
I'm not sure whether you're referring to the brake retarder discussion that R.Wold and I were having or the transmission cooler project in general.

I agree when you're looking at a number of these projects, they won't necessarily pay for themselves in terms of improved efficiency. But they may pay for themselves in other ways that are probably harder to quantify such as expected improved reliability or improved driving characteristics. In the case of the transmission cooler modification I did, that keeps the engine and transmission running at their optimal temps more often (all the time for the transmission), which is a good thing and can only help longevity. Doing something like a brake retarder helping safety, there's a benefit.

So the real question comes down to whether you want to do it and find the benefits worth the cost, not necessarily whether it's worth the investment cost. That's a personal decision, one I don't have to justify to any bean counters outside of my family. And my wife likes the work I do to the thing.

I don't expect that I'll be doing the brake retarder - although I would like to. The complexity and cost are both too high I think. But I am doing the electric cooling fan conversion.
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Old 12-27-2021, 03:03 PM   #11
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If you have a 6.7 Cummins with the VGT exhaust brake, you can add the PacBrake Loadleash P-67 engine brake to it. This will increase the engine braking power of the 6.7. The P-67 runs in conjunction with the VGT exhaust brake, it can not be used without it.
I have only driven Jake type engine brakes. I am getting a MH with the 6.7 and VGT exhaust brake. I will give it a try, but if I feel that it is not safe enough I will upgrade. Of course, the MH is not over 100k GVCW either.
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Old 12-27-2021, 06:32 PM   #12
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It appears that the P-67 may have been discontinued. Perhaps the 6.7 valve train was not up for the job. I emailed PacBrake, so I should find out for sure. If not, I'll land line them.
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Old 12-28-2021, 06:00 PM   #13
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I have a 3126B and an exhaust brake (butterfly valve) already.

Really, the engine braking works pretty well with this setup and the Teton Pass is the only time I ever felt it was marginal. I have enough other projects of higher priority that I don’t see myself attempting the transmission retarder, but maybe one day.

The transmission cooler continues to work perfectly. On our current winter trip we’ve been driving in temps in the mid teens (F). While I already knew the system would cool to my expectations, I wondered if it would overcool in the winter. This is part of why I mounted the coolers horizontally. The answer is no, they don’t overcool and the system continues to work great.
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