Thermo bypass valve on 68rfe transmission - Dodge Cummins Diesel Forum
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post #1 of 18 (permalink) Old 12-13-2019, 01:46 PM Thread Starter
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Thermo bypass valve on 68rfe transmission

Guess this valve goes bad and your transmission will overheat. ATS makes a replacement bypass valve for @$100 but I was wondering why cant you just cut the 4 lines and put in a couple of high temp rubber hoses with clamps and eliminate the tbv? Not under a lot of pressure so should work. Any thoughts?

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post #2 of 18 (permalink) Old 12-13-2019, 02:37 PM
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As soon as I figured out what a bad idea that thermostat block is, I rerouted my lines with half-inch transmission hose From Derale. 3/4 inch pex clamps are just the right size and make a really good looking installation. I silver soldered brass Barb fittings on the ends of all my steel lines to be sure they won't ever slip off. But that's probably overkill. Craig

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post #3 of 18 (permalink) Old 12-13-2019, 04:39 PM
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How many cases have you actually heard of the Thermo Bypass Valve failing? I get the concept, but the hype behind it is pretty deep with how many zillions are running around just fine without one.....

"This is a MUST for any truck that has a 68-RFE or Aisin AS69RC transmission or the Dodge HEMI with 545RFE, 65RFE, or 66RFE Transmissions in it. Dodge decides to incorporate a transmission cooler by pass valve into the cooling system of the 68-RFE and Aisin AS69RC that bypasses the transmission cooler during cold operation. The intent is to force the transmission to warm up faster, the reality is this bypass valve leaks and sticks in the bypass position in almost every case causing the transmission cooler flow to bypass the trans cooler essentially eliminating the trans cooler from the circuit. This causes a severe damage to the transmission over time. The ATS cooler block replaces the faulty design eliminating the bypass valve and ensures 100% of the trans cooler flow is forced through the trans cooler. In every case this substantially reduces transmission temperatures."
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post #4 of 18 (permalink) Old 12-13-2019, 05:07 PM
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I read the bypass is so the trucks get a few thousands more mpg by warming up the transmission sooner and that makes the EPA happy. I’m no expert but I’ve been into a couple of automatics and I’ve had a lot of them built and no transmission man has ever told me that it’s possible to over cool an automatic… Unless maybe you’re in Minot or Fairbanks. Craig

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post #5 of 18 (permalink) Old 12-13-2019, 05:19 PM
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I read the bypass is so the trucks get a few thousands more mpg by warming up the transmission sooner and that makes the EPA happy. I’m no expert but I’ve been into a couple of automatics and I’ve had a lot of them built and no transmission man has ever told me that it’s possible to over cool an automatic… Unless maybe you’re in Minot or Fairbanks. Craig
The friction material on your clutches wears less when the trans is warmer, even hotter.

Ford now has their transmissions running at the same temp as the engine coolant. For a while now. ZF told them to.

Metal likes heat to a certain extent. 500 degrees is bad but, in general, the hotter you can run it, the longer it will last and the more power it will put out in an engine. In a trans, the less it will wear.

Heat is energy. Energy is heat.

The problem is...... The working parts of the trans (and engine) can take the heat but the gaskets, seals, etc can not.

Ask any machinist. Trying to turn hot metal is a struggle. Gotta keep it cold in order to work it. Too hot and it won't do squat.

As to the EPA?? Whatever.

I know that my truck gets lousy fuel economy until the engine and trans get nice and toasty. I mean, heat-soaked toasty. On the highway, my first 150 miles kinda sucks. After that, I'm doing pretty good, mileage-wise.

Over-heating is bad, real bad. But right behind it is too cold believe it or else.
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post #6 of 18 (permalink) Old 12-13-2019, 09:49 PM
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Mine still gets to ~160 which is ~50* cooler than before. I'm very happy with that and shifting feels perfect. I don't get how some guys 68s only running ~130. Craig

2012 CCLB 4wd dually, 3.73, 68rfe, Fass, BD IH and E-brake kits. DD and towing machine.
Olde too soon... Schmart too late!
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post #7 of 18 (permalink) Old 12-13-2019, 10:33 PM
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Hopefully some more will chime in that have done alternate route.

I don’t want to sound like I’m raining on your parade but IMO the trans is the most important part of the truck so why try and save a few bucks there?

By the time you travel to pick up your hoses and other materials the amount you spend on diesel, clamps, and hose you’d be saving less than $80 vs a piece that is shipped to your door and manufactured to bolt in place without issue.

Keep us posted with what you come up with!
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post #8 of 18 (permalink) Old 12-14-2019, 01:02 PM
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To be honest, I've never even thought about this problem. I am much more concerned about line pressure since I made "changes." I even have my CTS2 set to sound an alarm that tells me to get out of the throttle for a second. The colder it is, the higher the pressure, of course. It seems to me that the faster the transmission gets up to normal operating temperature, the better.
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post #9 of 18 (permalink) Old 12-14-2019, 02:12 PM
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To be honest, I've never even thought about this problem.
Isn’t it amazing how the aftermarket can plant a seed in nearly everyone’s head by using buzz words such as “MUST” and “severe damage” and “faulty design”?

As others have already mentioned.....it’s a solution in SEARCH of a problem....a problem that is basically non-existent.

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post #10 of 18 (permalink) Old 12-14-2019, 07:30 PM
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Mine still gets to ~160 which is ~50* cooler than before. I'm very happy with that and shifting feels perfect. I don't get how some guys 68s only running ~130. Craig
Even when I'm towing my 8500lb TT in 100°+ temps my trans has only gotten to 176°, why mess with it? Empty driving in stop & go traffic it sits at 168°.
Also why would the by-pass valve stick if you keep your trans fluid clean with regular maintenance as it should be.
Like gsbrockman said the by-pass valve eliminator is a solution for a problem that doesn't exist.
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post #11 of 18 (permalink) Old 12-14-2019, 08:48 PM Thread Starter
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Like gsbrockman said the by-pass valve eliminator is a solution for a problem that doesn't exist....until your in the middle of the desert in 110 degree heat and your tranny goes boom...anyway im deleting the valve because you cant flush the tranny fluid unless valve is open, which means you have to drain/flush the tranny hot. Now with the valve deleted, I can do a tranny drain and flush when cold....because you have to disco the line at the radiator.
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post #12 of 18 (permalink) Old 12-16-2019, 08:25 PM
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Like gsbrockman said the by-pass valve eliminator is a solution for a problem that doesn't exist....until your in the middle of the desert in 110 degree heat and your tranny goes boom...anyway im deleting the valve because you cant flush the tranny fluid unless valve is open, which means you have to drain/flush the tranny hot. Now with the valve deleted, I can do a tranny drain and flush when cold....because you have to disco the line at the radiator.
So why bother to come here and ask for everyone's thoughts and waste our time?
You didn't get the answers you wanted and are going to do it anyway.
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