ATF Heat Exchanger Without Leaks

[illusha]

Summary – thinking about using one transmission cooler with ATF sandwiched in between two other transmission coolers full of coolant to create a durable heat exchanger – goal is to prevent blown tank separator walls and fluids mixing.

Need to add an oil-to-water heat exchanger for my 2006 Allison 1000 transmission in a custom 12-valve Cummins offroad truck to help transmission warm up to operating temp in cold weather. Heard too many stories over the years when either an internal radiator ATF tank leaks or a stand-alone heat exchanger (like on RAM or BMW or Nissan) busts a weld or somehow gets a hole in the wall separating fluids. Which usually leads to the transmission being flooded with coolant. My current HD radiator is made for coolant duties only with no other fluid ports. Additionally, Allison transmission cooler lines output 85 PSI at idle and can spike above 200-230 PSI under load, which is 2x-3x more pressure than most other car auto trannies and may exacerbate the “blown wall” issue.

Looked at a bunch of different heat exchanger designs, including marine, and most of them have flaws that can cause leaks. It’s also hard to find an ATF cooler or heat exchanger rated for over 300 PSI (many are 150 PSI rated). There’s only one unit by FSD called “Billet Aluminum Heat Exchanger” that seems pretty solid. But it’s pretty pricey too, of course, having been made from solid aluminum and low volume orders. So I was thinking about building my own “budget” version at least for now to experiment with.

My idea is to sandwich a Duramax cooler (rated for Allison’s higher line pressure) in between 2 other similarly-sized transmission coolers and fill the two outside ones with coolant. That way, the two outside units will fill up with the warm coolant and heat up the transmission fluid in between them when ATF is too cold and the truck isn’t moving yet (or plugged into a block warmer). This will also probably offer some degree of cooling and keeping steady operating temperatures under normal use too. And then run an additional Duramax cooler in front of the radiator to actually cool the fluid down when truck is moving and tranny gets too hot.

Thoughts? Feedback? Criticisms? Suggestions for improvement? Alternatives to consider?

 

[Rand]

Why does it need help warming the transmission fluid?
seems overcomplicated and reinventing the wheel.

 

[SHOZ]

Can you use a remote mount filter and the use a water oil filter type heat exchanger?

 

[Pew]

I offer no experience with this platform or your intentions other than to say when we stuck an 4" intercooler on the Evo where it's in front of the coolant radiator, we were getting high coolant temp issues and general airflow issues within the engine bay. I feel like your plan is too complicated and may create other issues.

Does the ATF have the same operating temp as the coolant? My other concern here (just thinking out loud, don't know if it's true) is what if there's no airflow and now your coolant temp is making your ATF fluid unnecessarily hot or vise versa.

 

[illusha]

Let me provide some additional info. The truck has a mechanical Cummins engine with OEM Intercooler/Radiator from a 1997 Dodge RAM and an Allison 1000 tranny from a 2006 Chevy Silverado Duramax. I was able to swap the original Dodge intercooler and radiator in an OEM-like configuration and even radiator hoses are unchanged from stock shapes.

Factory Cummins trucks needed HD cooling for towing and so that’s all their radiators do – pass coolant – automatic RAM trucks of all generations have a standalone plate heat exchanger plus a cooler in the grille. Problem with using that one is that Dodge transmissions are lower pressure with spikes just over 100 PSI and still those heat exchangers occasionally blow through precisely because of these pressure spikes (which is what inspired the FSD Billet unit). There are other similar external plate heat exchangers in BMWs and Nissan trucks, as well as some newer model vehicles, and they all have stories of the coolant ruining the tranny.

Factory Duramax with Allison trucks have a transmission heat exchanger built into the side of radiator plus a cooler in the grille. Those radiators don’t have enough flow for a Cummins and, although not as common, are still known to occasionally blow the internal tank and send coolant to mix with transmission fluid. Both radiator side tank and the front cooler have threaded fittings that can withstand 200+ PSI pressure unlike hose clamps on many other coolers.

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. It’s generally expected that transmission is maybe just 10-20 degrees cooler than engine oil because transmission doesn't generate as much heat and is still plumbed to the "cold" side of the radiator.

When transmission temperature starts warming up, like in stop-and-go traffic or when climbing a big hill under load, then the heat exchanger actually also provides cooling for transmissions and works enough to cool at least non-HD ones down to safe temps. In fact, many vehicles only have that internal heat exchanger in the radiator, not all cars and trucks have an additional air cooler. People that frequently give their transmissions a good work out often upgrade their front air coolers to bigger sizes with electric fans and that was my plan as well.

I’ve thought about using a sandwich adapter on the spin-on Allison filter, but the same issue, those adapters do leak occasionally. Don’t want to use a submersible-type heater element that screws into the drain plug because they are meant to keep the fluid warm when it’s already warm and can scorch the fluid when used to heat it from cold. Plus there are reports of problems when pre-warmed tranny fluid suddenly flows through ice cold parts. So it’s best to warm it up by circulating it. Someday I will have a PTO and can just run that to warm up the fluid. But that’s a separate project.

For now, I’d like to find a way to gradually bring the fluid up to normal operating temperature as the truck is idling and warming up, which is best done with a heat exchanger. I suppose I could drop the dough on the FSD Billet one or have a custom radiator built. But I kinda like improvising with parts available off the shelf because I break things. I also wonder which design would actually work to transfer heat better (two welded or billet reservoirs sandwiched together VS two or three identical transmission coolers sandwiched together). Thus this thread.

 

[clinebarger]

Radiator mounted coolers (Coolant to ATF) provide very little if any at all in the way of heating the ATF, A lot of manufacturers use thermostatic cooler bypasses so the trans can warm itself up via Converter Slip.

For their size....You can't beat a Coolant to ATF Cooler for efficiency, An Air to ATF Cooler needs to be much larger (2-3 times) to have the same cooling efficiency.

Tru-Cool & Setrab sells some pretty large Air to Oil/ATF coolers.