Dual Derale Transmission cooler upgrade

[Pudgy Camper]

BACKSTORY........Last year after I purchased my 04 Windsor, I became obsessed with getting it up to date on maintenance and correcting any issues that were present or could become a problem in the future. One of the first items that received an overhaul was the engine cooling system. This included a new water pump, thermostat, hoses, tubing and expansion tank. The factory cooling design included a transmission fluid cooler/heat exchanger connected with a couple of short 90 degree hoses and a couple coolant tubes. For those that aren't familiar with this style of transmission fluid cooler, they have an internal core that the trans fluid runs through and depends on the surrounding antifreeze/engine coolant passing over it to cool the trans fluid. This design works well but is lethal to the transmission if an internal leak ever develops and contaminates the transmission. I've never been a fan of this style of mixed fluid cooling and decided go ahead and upgrade to a stand alone fan controlled remote cooler. In doing so, I was able to simplify the hose/tubing layout and keep my transmission fluid separated from any chance of engine coolant contamination. Here is the old equipment vs the new equipment. 

 Before I go any further, I should give credit to numerous members on this forum ( especially jacwjames), others on IRV2 and also Ted from the YouTube channel 'Teds Garage' for the encouragement and tips to making this cooling system work like it should. Ted has a great video on how he did this mod on his Allison 3000 and explains everything way better that I can.

Anyways ...I ended up using a Derale Hypercool Extreme part #15876 for the cooler. It was the only one I could find with 12AN fittings (same as my Allison 4000 transmission). I had new hydraulic lines built to run from the transmission to the new fan. I mounted the fan on the frame of the coach, rearward of the radiator stack. I used a snap disc temp switch mounted to the side of the Derale cooler to control the fan along with a relay to power the fan. I ran wiring to cockpit with a LED light to show me when the fan was running and an override switch to be able to turn on the fan manually if needed. This setup performed good, but had a few flaws. The snap disc switch was inconsistent and I found myself using the over ride switch as the main temp control and usually just let the fan run constantly. Last summer when retuning from up north back to Phoenix, it was 115 ambient temp and my transmission temp was staying around 198 with the fan running non-stop. Not bad, but I knew I could improve the whole setup.

Fast forward to summer 2024....after discussing with Ted, I decided to add a second fan. I was also able to find a Setrab 12AN fitting with a internal thermal couple to use as a switch instead of the snap disc. This style temperature switch is in direct contact with the trans fluid. The next challenge was to find space for both coolers. I ended up building a custom frame to fit up in the rear corner of the coach, behind the radiator stack but in front of the air filter. I had to have my hydraulic hoses fitted with straight fittings (instead of 45s used with my single cooler build) and also a short jumper hose built to connect the two coolers. I added a second relay to control the second fan and both fans can be manually tuned on at any time by the over ride switch next to the drivers seat. Here's some pictures of the final product.

 

Here's the parts I used:

(2X) Derale Hypercool Extreme Cooler #15876

(1X) Setrab SET31-TS180-12

(2X) 12v Automotive relays

12vdc switch, 12vdc LED

2 New hydraulic hoses to the transmission and 1 short jumper to connect the 2 new coolers.

Total cost.... probably around $1100, a lot of sweat and many, many hours!

I will report back after a trip up to the mountains next month. I could have probably gotten by with the single cooler and just ran the fan full time, but I feel more confident in having two and I'm hopeful the new Setrab switch will be more consistent with only turning the fans on when needed.

 

 

Edited August 8 by Pudgy Camper

[jacwjames]

I had a single Derale mounted in series with the cooler in the radiator.  I was performing well.  On a trip last year in UT the core on the Derale started to leak.  I had pulled off the highway near Mohab and stopped at a campground.  At the time I did not know the cooler was leaking.  By chance I had trouble with my jeep and there was a mechanic at another campground who agreed to look at it and I made arrangements to move there, it was 1/4 mile away, but when I went to move the tranny would not shift out of 1st gear.  Parked my rig and went around back and found the leak.  I ended up bypassing the Derale cooler, but had to add 3 gallons of oil, luckily no damage to the tranny.  Continued my trip ~2500 miles home.  Took an oil sample and it came back good, I got lucky.   But no more Derale for me. 

I ended up buying a used oil cooler normally used on a rear radiator coach.  These are HD  built.  I did use the fan from the Derale.  Works great, I set up data logging on my Silverleaf to monitor the temps and they ran between 165- 175. 

Edited August 8 by jacwjames

[jacwjames]

For the owners of coaches with the internal cooler, there was a recall on several models of coaches in ~2001-2003.  Attached is a TSB with serial number ranges of coaches by model. 

Last year I know of 2 coaches that had failed internal tranny cooler requiring new radiators and tranny.  ~$$$$$ repair.  The failures are instantaneous, no real tests can be done to predict or prevent.   

Although the original poster had an external tranny cooler it still needs coolant running through it to work so there is a possibility of cross contamination.  He has come up with a viable solution to improve cooling and eliminate the possibility of cross contamination.  

I know that @vanwill52 preemptively made this change and provided me info on how he did it.   My final solution to bypass the radiator is a cloned version of his solution which is probably the way to go.  It improves tranny cooling plus reduces stress on the engine cooling. 

Technical Service Bulletin for Radiators Monaco.pdf

[Pudgy Camper]

13 hours ago, jacwjames said:

I had a single Derale mounted in series with the cooler in the radiator.  I was performing well.  On a trip last year in UT the core on the Derale started to leak.  I had pulled off the highway near Mohab and stopped at a campground.  At the time I did not know the cooler was leaking.  By chance I had trouble with my jeep and there was a mechanic at another campground who agreed to look at it and I made arrangements to move there, it was 1/4 mile away, but when I went to move the tranny would not shift out of 1st gear.  Parked my rig and went around back and found the leak.  I ended up bypassing the Derale cooler, but had to add 3 gallons of oil, luckily no damage to the tranny.  Continued my trip ~2500 miles home.  Took an oil sample and it came back good, I got lucky.   But no more Derale for me. 

I ended up buying a used oil cooler normally used on a rear radiator coach.  These are HD  built.  I did use the fan from the Derale.  Works great, I set up data logging on my Silverleaf to monitor the temps and they ran between 165- 175. 

Thanks Jim, that's a good setup you have there. The only thing that I don't like about the Derale is they do seem a little light weight. I may keep an eye out for an HD oil cooler similar to yours that would work for me. I wish I had the rear open area like you have. I originally tried to squeeze my single derale in that area but my air filter occupies the majority of that space. What are you using as a fan control switch? Still using the snap disc?

[jacwjames]

Yes, I am still using the snap disc, works good and my temp is hovering 165-175. 

When my Derale failed I contacted Derale, they did warranty it but I decided not to use.  They said that the problem was probably the weight of the hose on the Derale and vibration.  But when I first installed I made sure the fittings did not put any strain on the Derale.  When I took the bottom hose loose where the leak was it stayed right in place, so I don't think that was the problem. 

[hitechpete]

When my coolant radiator began to leak on my 2000 Diplomat, I bypassed the internal transmission intercooler and replaced it with an automotive oil cooler. I mounted it on a frame attached to the radiator mounts, on the outside of the radiator (towards the doors) which worked perfectly well over here in the UK. The only downside of removing the intercooler is the loss of heating to the transmission when ambient temperatures are very low, once again not a problem in the UK, but which could be an issue in the colder states in the USA.

Nice work by the way.

[jacwjames]

3 hours ago, hitechpete said:

When my coolant radiator began to leak on my 2000 Diplomat, I bypassed the internal transmission intercooler and replaced it with an automotive oil cooler. I mounted it on a frame attached to the radiator mounts, on the outside of the radiator (towards the doors) which worked perfectly well over here in the UK. The only downside of removing the intercooler is the loss of heating to the transmission when ambient temperatures are very low, once again not a problem in the UK, but which could be an issue in the colder states in the USA.

Nice work by the way.

Yes, good point and it is something I know I have to watch but luckily I don't travel it really cold weather a lot.  The snap disc I use is a 155F so it won't come on until tranny is pretty warm. 

But the rear radiator coaches use the same setup so I think it will work.

[Mick Adair]

On 8/9/2024 at 9:15 AM, jacwjames said:

For the owners of coaches with the internal cooler, there was a recall on several models of coaches in ~2001-2003.  Attached is a TSB with serial number ranges of coaches by model. 

 

Just to make sure, is the serial number of the coach the blue tag by the entry door?

[jacwjames]

1 hour ago, Mick Adair said:

Just to make sure, is the serial number of the coach the blue tag by the entry door?

I believe so, yes

Also listed on the data/build sheet and MSRP

[Mick Adair]

OK good. That means my radiator is outside of the recall range. I’m going to be keeping my eye open for a good deal on a heavy duty cooler though.

[jacwjames]

I bought a used one from Visione RV. https://rvchassisparts.visonerv.com/cgi-bin/md/M120007/s1.pl?

 

[Benjamin]

On 8/11/2024 at 4:49 AM, hitechpete said:

... The only downside of removing the intercooler is the loss of heating to the transmission when ambient temperatures are very low, once again not a problem in the UK, but which could be an issue in the colder states in the USA...

I've considered this, but I don't think it applies. The transmission may have a thermostat in the cooler line, I haven't found proof, but some things hint at it.  The bigger factor is the transmission cooler is always in the cold side of the radiator, I don't think it warms the transmission fluid except in very short, and unusual situations.  If it's -40, then the cold side of the radiator will be -35 or even colder, the engine thermostat will not open until the engine is under a significant load and then it will only crack open and shut almost immediately.  Maybe nobody drives an RV in -40, but trucks have the same setup, and it will apply similar at 20F, and probably even at 50F.  The transmission cooler in the radiator is just not capable of consistently heating the transmission fluid.  This is different from an oil cooler in the engine block, that is controlled by the thermostat so stays near 180, or the thermostat setting, at least while the thermostat is mostly closed.

[hitechpete]

Quick Google search reveals:

The general idea is that every automatic transmission should have both an oil-to-water heat exchanger and an oil-to-air cooler. Heat exchanger serves two purposes. It warms up the transmission when it's cold to help it reach the proper operating temperature quicker

[Pudgy Camper]

Just wanted to give an update on my new transmission cooler set up. I just returned from a 2000 mile round trip to Texas and the dual cooler setup worked perfect. Ambient temps ranged from 80-105 degrees on travel days, and the warmest I saw the transmission temp was 190. Most of the trip it was between 165-180. The Setrab thermal switch kicked the fans on at 185 and turned them off at 165 just as designed and I never once had to use my manual override switch. So for now, this project is a success!