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 > Revmax 68RFE Transmission Cooler Thermostatic Bypass

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ShinerBock

SATX

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Posted: 04/26/19 10:42am Link  |  Quote  |  Print  |  Notify Moderator

My re-builder recommended this upgrade when I had my custom trans built. I have been running it for several months now and finally had a chance to tow with it in. All I can say is wow. This is a must have mod for those who tow with their 68RFE even with a completely stock truck if you are seeing high trans temps.

Those that own a 68RFE know that it is notorious for running hotter than most other transmissions. I used to think that it was due to design until I replaced my thermostatic bypass valve with this Revmax one which is advertised to improve flow to the cooler by over 80% and decreases trans temps by as much as 50F. I can attest that it decreased the temps by as much as 30F empty and 20F towing in my truck.

The stock one purposely reduced flow to the cooler in order get the trans temps hotter quicker in colder weather. The problem is that many times it gets stuck or partially stuck in this closed position causing temps to spike inside the trans. Not only that, but the stock valve itself is a very restrictive bottleneck. My re-builder started recommending these bypass valves after seeing several of them fail causing the transmission to fail.

68RFE Transmission Cooler Thermostatic Bypass Upgrade

* This post was last edited 04/26/19 12:49pm by ShinerBock *   View edit history

IdaD

Idaho

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Posted: 04/26/19 11:06am Link  |  Quote  |  Print  |  Notify Moderator

What temps were you seeing when you were towing stock versus now? My truck is totally stock and I've never had problems with the trans overheating.


2015 Cummins Ram 4wd CC/SB


ShinerBock

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Posted: 04/26/19 11:28am Link  |  Quote  |  Print  |  Notify Moderator

IdaD wrote:

What temps were you seeing when you were towing stock versus now? My truck is totally stock and I've never had problems with the trans overheating.


Mid 180F depending on outside temps. It is not uncommon to get up to 110F here in south Texas. It is also very intermittent too. Sometimes it will go passed 175F and towing the same trailer in the same conditions another day will never even get to 175F which leads me to believe I may have had a valve that was partially stuck every now and then. Now it stays in around 160F when towing.

* This post was edited 04/26/19 11:53am by ShinerBock *

ShinerBock

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Posted: 04/26/19 11:51am Link  |  Quote  |  Print  |  Notify Moderator

Here is a video from ATS about how the stock valve operates.


ATS Diesel - Thermal Bypass Valve

IdaD

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Posted: 04/26/19 01:39pm Link  |  Quote  |  Print  |  Notify Moderator

ShinerBock wrote:

IdaD wrote:

What temps were you seeing when you were towing stock versus now? My truck is totally stock and I've never had problems with the trans overheating.


Mid 180F depending on outside temps. It is not uncommon to get up to 110F here in south Texas. It is also very intermittent too. Sometimes it will go passed 175F and towing the same trailer in the same conditions another day will never even get to 175F which leads me to believe I may have had a valve that was partially stuck every now and then. Now it stays in around 160F when towing.


Interesting. Mine seems to consistently run around 168 towing regardless of outside temperature.

ShinerBock

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Posted: 07/16/19 07:28am Link  |  Quote  |  Print  |  Notify Moderator

Finally replaced the bypass valve in my brothers 2014 Ram a three weeks ago. He started noticing that his is temps were spiking higher than normal(even for 100F outside temps) when he was hooking up his RV several weeks ago with the truck running in park for just 5-10 minutes and the trans temps got up past 200F. He also started seeing that his temps rose higher than normal when in park longer than five minutes in other situations as well. Towing, his temps would get to the 190F's when they usually were well below that. This led us to believe that the thermostat in this valve was acting up like mine was causing the higher than normal temps.

He did his first tow to Rockport a few weekends ago. Temps never got past 170F towing in 90-95F heat where previously it would get closer to 190F. Unloaded, temps stay around 150F where they were 170F to 175F before. The big test was going across the ferry. He was in line for 30 minutes and his temps never got past 180F where before they would have gone past 200F.

My temps are a little higher than his in the same conditions since I have much higher line pressure than he does due to having a trans built to handle 700 hp.

This time I took pictures of the OE valve since I replaced it for him. As you can see, the line going to the cooler is blocked by a thermostat causing a major restriction. I heated the valve up passed 170F and it barely opened to allow fluid to flow. The Revmax valve (which I didn't take a picture of) is a flow through design like the cooler to transmission side of the OE valve is, but much larger diameter port allowing more fluid to pass through to the cooler unrestricted.

The top of the valve.
[image]


From cooler to trans port, trans side.
[image]


From trans to cooler port, trans side.
[image]

From trans to cooler port, cooler side.
[image]

* This post was last edited 07/16/19 08:14am by ShinerBock *   View edit history

Grit dog

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Posted: 07/16/19 11:04am Link  |  Quote  |  Print  |  Notify Moderator

Thanks for the informative post!
Unlike newer engines, I don’t subscribe to “hotter is better” for transmissions.
It bugs me that my company truck runs 190-200 ALL the time, according to the gauge anyway. Empty or loaded. Runs the same temp towing uphill as empty downhill, or close enough.
It also blew the trans at 60k miles. New one still runs 190s.


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Bionic Man

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Posted: 07/16/19 12:37pm Link  |  Quote  |  Print  |  Notify Moderator

I’ve been paying a lot more attention to trans temps since my concern with my Yukon.

I’ve come to the conclusion that 200* empty is nothing unusual in newer vehicles. My Yukon runs it. My RAM is there. My Grand Cherokee is there. The Traverse I rented two weeks ago was there. And the Grand Cherokee I’m renting right now is running that temp.


2012 RAM 3500 Laramie Longhorn DRW CC 4x4 Max Tow, Cummins HO, 60 gallon RDS aux fuel tank, Reese 18k Elite hitch
2003 Dodge Ram 3500 QC SB 4x4 Cummins HO NV5600 with Smarty JR, Jacobs EB (sold)
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ShinerBock

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Posted: 07/16/19 01:42pm Link  |  Quote  |  Print  |  Notify Moderator

Normal temp of each brand and transmission depends on where the temps sensor is, what kind of trans fluid is used, line pressure used by the trans(generally more horsepower/torque = more line pressure to hold the clutches), and the design of the trans. The stock 68RFE is notorious for burning up over drive clutches especially when power is added so I prefer to keep the temps as low as possible.

My car has the 8hp and the trans normally runs around 195F. However it uses different fluid, is mated to an engine with a lot less horsepower/torque, is moving a much lighter vehicle, and is designed differently than the 68RFE in my truck. Most importantly, it reads its temp from the trans to the cooler which tend to show hotter temps than the sump temperature where the 68RFE gets its temp.

Cummins12V98

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Posted: 07/16/19 02:06pm Link  |  Quote  |  Print  |  Notify Moderator

180 is nothing to be concerned about. My 68 towing in HOT weather on grades at 29 k was in the 170’s and only time over 200 towing in town.


2015 RAM LongHorn 3500 Dually CrewCab 4X4 CUMMINS/AISIN RearAir 385HP/865TQ 4:10's
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