Thermal bypass - Page 2 - Dodge Cummins Diesel Forum
4th Gen Powertrain Discussion of components that are directly involved in the power production and all that is needed to get and keep the truck moving . Engine, Transmission, etc...NO ADVERTISING

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post #13 of 19 (permalink) Old 06-18-2019, 01:09 PM
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Would have been a normal 1 beer job except for the way the lines fit.

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2013 RAM 2500 diesel 6.7 Bighorn Crew Shortbed 4x4 in white. As of 7/21/16 16,100 miles.
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post #14 of 19 (permalink) Old 06-18-2019, 01:36 PM
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That thermostat is there to get the transmission and fluid hotter so there is less drag from thick fluid. I took the thermostat cartridge out of mine and made a plug to drive into the center of the block so that flow is always to the cooler and my trans ran 20 Cooler. I’ll take a cooler transmission over hotter any day. I’ve known a lot of transmission builders who told me they never heard of overcooling an automatic. Do a search on automatic transmissions and heat and you’ll see how as heat goes up life of the transmission goes down. My truck came with the max tow welded plate exchanger which is basically another fluid heater because it supposedly cools the fluid with engine water. I did away with that exchanger and replaced it with a fan powered remote Derale cooler and now my transmission runs 150 towing. Craig

2012 CCLB 4wd dually, 3.73, 68rfe, Fass, Deleted, EFI engine/trans tuning, BD IH SXE 363/80/.91 w/ebrake, 4" turbo back/51" Quiet Tone. DD and tow vehicle.
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post #15 of 19 (permalink) Old 06-18-2019, 06:50 PM
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Do a search and read about how transmissions life goes down as temperature goes up. That thermostat block wasn’t put there to make the transmission last longer. Craig

2012 CCLB 4wd dually, 3.73, 68rfe, Fass, Deleted, EFI engine/trans tuning, BD IH SXE 363/80/.91 w/ebrake, 4" turbo back/51" Quiet Tone. DD and tow vehicle.
Olde too soon... Schmart too late!
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post #16 of 19 (permalink) Old 06-18-2019, 06:52 PM
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Sorry for the duplicate post but my phone was not showing me my earlier post.

2012 CCLB 4wd dually, 3.73, 68rfe, Fass, Deleted, EFI engine/trans tuning, BD IH SXE 363/80/.91 w/ebrake, 4" turbo back/51" Quiet Tone. DD and tow vehicle.
Olde too soon... Schmart too late!
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post #17 of 19 (permalink) Old 06-18-2019, 08:23 PM
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I installed the revmax one on my 18 and my unloaded temps went from 165 average to 120 average. It took all of 10 min to install. Lost virtually no fluid
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post #18 of 19 (permalink) Old 06-19-2019, 02:04 AM
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Automanfactures try their best to save even a fraction of a penny.

Knowing this, why would RAM install this? When just using straight lines, it would be much cheaper.

As BFD brought up, its to help the oil reach a set operating temperature. However, we all know that the cooler an Automatic the better. So, why would RAM want it at a set temperature?

Hotter oil flows better and "sucks" less power than cold oil. Also, you want the transmission to get hot enough to evaporate any water in the oil. Finally you have thermal heat transfer. The hot oil needs to remain in the cooler long enough for the air to extract the heat. Move the fluid too fast, and not all the heat will be removed. You may not notice this when operating under the limits of the cooler or not making heat in the transmission. However, under extreme conditions, the thermostat based system may cool better.

Finally, the transmission shifts differently based on temperature. When cold, it holds the lower gears longer. If you live in a cold climate it will take much longer for trans to reach this set temperature, affecting your MPG.


As I live just north of actual HELL, I'll delete my transmission thermostat.

I'm a firm believer that a cool transmision is a happy transmission.
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post #19 of 19 (permalink) Old 06-23-2019, 01:31 PM
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Yep, fluid cooling is forgiving. If the flow is faster there is less heat exchange but the fluid passes through more often. The net affect isn't as drastic as the flow changes. No exchanger is 100%... You will never have 0* approach. Keeping exchangers clean is also critical. Approach temp goes up when the surfaces are dirty. That might be why some guys get more benefit from the tstat bypass... The air cooler is more plugged with bugs and dirt than the next guys cooler.
An extra bonus from cooler temp is firmer shifting. A Protect 68 or VB WAS going to be my next mod but I wouldn't want it shifting any harder than it does now. It's on the borderline of slamming, when in tow/haul. I think it's just right but that wasn't planned... I'd rather be "lucky" than "good", any day! Craig

2012 CCLB 4wd dually, 3.73, 68rfe, Fass, Deleted, EFI engine/trans tuning, BD IH SXE 363/80/.91 w/ebrake, 4" turbo back/51" Quiet Tone. DD and tow vehicle.
Olde too soon... Schmart too late!
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