8hp70 heater bypass

[Missouri2016]

I have been following this thread for a couple of weeks and wanted to post what I have experienced. I have 2016 1500 Laramie that I bought new in 2017. Had issues with the original transmission doing the hard bump from 2-1 gear in 2019. After a year of back and forth with the dealer, they finally replaced after I started a claim with FCA. It shifts great but 2 weeks ago coming back from the lake, we noticed a high pitch whining on the highway when it downshifted and the trans temp was almost 240 F. It shifted fine and as soon as I got off the highway, the trans temp was down to 185. Driving it back and forth to work doesn't get it hot enough, so I drove for about 30 minutes on the highway(without the trailer) and it got up to 225 F. Again, as soon as I got off the highway, back down to cooler temps. After reading your posts, I went ahead and bought a new Heater assembly from the dealer and installed it($173.00) The dealer was kind of a **** about installing it($704.00 installed BTW) and they couldn't get to it for 3 weeks. Took me probably about 6 hours to do it, plus refilling the coolant level and trans fill procedure. I also installed a new factory thermostat and added new coolant. Took it out Saturday, and it ran 185 the whole time and coolant temps were 204-215 and no whining. Next, I removed all but the upper and lower shutters, and the coolant temp never got over 208.
Here's the interesting part:
Running down the highway (no trailer) at 75 MPH and no A/C running, the trans temp crept up to 193. I turned on the A/C, which kicked on the electric fan, and the temp dropped right back to 186-188 the whole time. I wonder if the A/C fan sitting idle disrupts the airflow and that's why it cools down when its on. You would think though that at 75 MPH there would be more than enough flow.
Question: By switching to a lower thermostat(180°) will it throw a CEL? All stock now and no tuner. Also, I'm not sure if I'll put one of caulk04's bypass valves in, but I would like to purchase one.
BTW, that heating unit was a b***h to remove. Spring clamps on the coolant hoses were tough to get at, and the trans fittings did not want to release, even with the correct tool. I wound up just pulling the e-clips with a screwdriver. Installation was easy.

 

[Wild one]

I have been following this thread for a couple of weeks and wanted to post what I have experienced. I have 2016 1500 Laramie that I bought new in 2017. Had issues with the original transmission doing the hard bump from 2-1 gear in 2019. After a year of back and forth with the dealer, they finally replaced after I started a claim with FCA. It shifts great but 2 weeks ago coming back from the lake, we noticed a high pitch whining on the highway when it downshifted and the trans temp was almost 240 F. It shifted fine and as soon as I got off the highway, the trans temp was down to 185. Driving it back and forth to work doesn't get it hot enough, so I drove for about 30 minutes on the highway(without the trailer) and it got up to 225 F. Again, as soon as I got off the highway, back down to cooler temps. After reading your posts, I went ahead and bought a new Heater assembly from the dealer and installed it($173.00) The dealer was kind of a **** about installing it($704.00 installed BTW) and they couldn't get to it for 3 weeks. Took me probably about 6 hours to do it, plus refilling the coolant level and trans fill procedure. I also installed a new factory thermostat and added new coolant. Took it out Saturday, and it ran 185 the whole time and coolant temps were 204-215 and no whining. Next, I removed all but the upper and lower shutters, and the coolant temp never got over 208.
Here's the interesting part:
Running down the highway (no trailer) at 75 MPH and no A/C running, the trans temp crept up to 193. I turned on the A/C, which kicked on the electric fan, and the temp dropped right back to 186-188 the whole time. I wonder if the A/C fan sitting idle disrupts the airflow and that's why it cools down when its on. You would think though that at 75 MPH there would be more than enough flow.
Question: By switching to a lower thermostat(180°) will it throw a CEL? All stock now and no tuner. Also, I'm not sure if I'll put one of caulk04's bypass valves in, but I would like to purchase one.
BTW, that heating unit was a b***h to remove. Spring clamps on the coolant hoses were tough to get at, and the trans fittings did not want to release, even with the correct tool. I wound up just pulling the e-clips with a screwdriver. Installation was easy.

The TMU can be a royal pain to remove when the transmission is in the truck,lol. Only way to find out if your truck will throw a code with the 180 t-stat is to install it,the odd truck will throw a code,but the majority of trucks don't.The ones that seem to throw a code are trucks that see colder winter temps,where you live odds are you won't get a code. The transmission cooler is in the top part of the A/C condensor,how bug infested is your A/C condensor,if it's a bit clogged you could pull the grill and run it through your local coin-op carwash and hose it clean,that's actually the first thing i'd try,and go from there

 

[Missouri2016]

I'll pull the grill again this week and give it a good cleaning. It looked clean,but I didn't really focus on it yesterday. I think I'll but a thermostat, and give it a try. I've been towing the same boat now for four summers, and never had any issues. Thanks for the input.

 

[BlownGP]

I'll pull the grill again this week and give it a good cleaning. It looked clean,but I didn't really focus on it yesterday. I think I'll but a thermostat, and give it a try. I've been towing the same boat now for four summers, and never had any issues. Thanks for the input.

It shouldn't throw a code like Wild said unless you are in a cold climate for a long period of time.
And the code doesn't hurt anything. The truck drives fine. It just comes on because the truck thinks something is wrong because it takes a little longer to get up too temp or not the right temp.

Funny thing is, my 09 throw a code when it was really cold out. My 2018 has yet to throw one and we had two 20* days back in February.

 

[hawsk99gt]

Funny, I didn't mention the other day that after I removed all my AGS shutters (except for the tops and bottoms) I ran over to the automated car wash. So I wonder if my AC Cooler got cleaned? I'll have to look at that this week when I replace my PCV valve. Haven't done that yet and I am at almost 100K. By the way, nice input.

 

[Shawn Burns]

It shouldn't throw a code like Wild said unless you are in a cold climate for a long period of time.
And the code doesn't hurt anything. The truck drives fine. It just comes on because the truck thinks something is wrong because it takes a little longer to get up too temp or not the right temp.

Funny thing is, my 09 throw a code when it was really cold out. My 2018 has yet to throw one and we had two 20* days back in February.

I've been running a 180 thermo for two years now with no codes or problems. Coolant temps go between 185 and 205 while towing, depending on hills, etc.

 

[wellsj89]

Does anyone have a stock thermostat and spring they are willing to sell? On my ecodiesel I put in a bypass and want to revert back to stock. For the life of me I can’t remember where I put my stock parts. Been having some harsh shifts and the guy who tuned my transmission said the tune is based off operating temps so it might act strange if it never gets to them. Thanks in advance

 

[hawsk99gt]

I have a question. If and when I bring my truck to the dealer to replace my transmission under warranty, (which I think is going to happen) do you guys think I will need to undo CAULK's Heater By Pass and put my AGS panels back in place? The reason I say this now is because the truck is starting to do what it did originally on the first transmission that got replaced at 60k miles. Come to a stop and get a slight bump, like someone just tapped you from behind. Let me know what you think.

 

[JHoward]

I have a question. If and when I bring my truck to the dealer to replace my transmission under warranty, (which I think is going to happen) do you guys think I will need to undo CAULK's Heater By Pass and put my AGS panels back in place? The reason I say this now is because the truck is starting to do what it did originally on the first transmission that got replaced at 60k miles. Come to a stop and get a slight bump, like someone just tapped you from behind. Let me know what you think.

Imo, I would take the Caulk transmission t-stat bypass out and use it on the next transmission ... may not be an bad idea to put the AGS slats back in, just in case.

You never know what the dealer might say or think if they notice something has been altered ... then again, they might not notice anything, but I'd still keep the Caulk t-stat bypass.

 

[Wild one]

I have a question. If and when I bring my truck to the dealer to replace my transmission under warranty, (which I think is going to happen) do you guys think I will need to undo CAULK's Heater By Pass and put my AGS panels back in place? The reason I say this now is because the truck is starting to do what it did originally on the first transmission that got replaced at 60k miles. Come to a stop and get a slight bump, like someone just tapped you from behind. Let me know what you think.

I would,just to save the head-aches you might run into with a warrenty claim. FCA/Stellentis are famous for denying warrenty over any little thing they can

 

[hawsk99gt]

I would,just to save the head-aches you might run into with a warrenty claim. FCA/Stellentis are famous for denying warrenty over any little thing they can

well then I'm waiting for it to throw a code like last time and then do that. Cause they won't do the job right away. First they have to order the transmission which takes forever. So when they say its ready I'll bring it over with everything put back in place.

 

[NETim]

If I understand this correctly, the bypass kit bypasses the transmission heater. Does this mean there's no more fluid flowing through the heater? What's the heater doing now? Is the transmission boss still commanding the heater to continue to produce heat?

Just curious.

TIA.

 

[Wild one]

If I understand this correctly, the bypass kit bypasses the transmission heater. Does this mean there's no more fluid flowing through the heater? What's the heater doing now? Is the transmission boss still commanding the heater to continue to produce heat?

Just curious.

TIA.

It doesn't bypass the heater,it bypasses the thermostat that controls transmission fluid flow to the cooler in the top of the A/C condensor.This is totally seperate from the coolant heater,there'll still be coolant circulating through the thermal unit.If you go through this thread,you'll see the thermal heater is a seperate deal from the plate that has the thermostat.

RevMax 8 speed thermostat bypass

Took the wife out for supper tonight,we weren't in any rush and we were on 2 lane back roads,so i had the cruise set at 90 kmh's roughly 56mph,our favorite little eating joint is about 40 miles away,tranny just barely got over 110f in her car.

www.ramforum.com

 

[NETim]

It doesn't bypass the heater,it bypasses the thermostat that controls transmission fluid flow to the cooler in the top of the A/C condensor.This is totally seperate from the coolant heater,there'll still be coolant circulating through the thermal unit.If you go through this thread,you'll see the thermal heater is a seperate deal from the plate that has the thermostat.

RevMax 8 speed thermostat bypass

Took the wife out for supper tonight,we weren't in any rush and we were on 2 lane back roads,so i had the cruise set at 90 kmh's roughly 56mph,our favorite little eating joint is about 40 miles away,tranny just barely got over 110f in her car.

www.ramforum.com

Okay! Thanks for the clarification!

 

[caulk04]

The easiest way to think of it is that my part is a 'stuck open thermostat'. The system behaves exactly as it would with the thermostat open.

Coolant still flows through the heat exchanger block as normal, the trans fluid just takes the cooler circuit instead of through the heater circuit.

 

[NETim]

Just finished the install of the bypass. It wasn't what I consider an "easy" project but very doable.

I put jackstands under the truck fore and aft on the driver's side to get more maneuvering room under the truck.

I had to drop the driveshaft to get at the mounting bolts for the 2 shift bracket mounting bolts (T40). I don't know how this step can be omitted. I made this job harder by not cleaning up the rust on the exposed portions of the 4 driveshaft mounting bolts. This made getting the bolts out difficult to say the least, even with liberal amounts of penetrating fluid on them. After I wised up and cleaned them, I got all 4 out by carefully working the bolts in and out until they were finally free.

I am spoiled by the clean and rust free environment of a hospital radiology department. CT's and MRI's aren't exposed to much dirt, slime and road salt. Not like the underside of a 9 y/o truck. Wrenching on imaging equipment usually doesn't involve penetrating oil.

I pulled the shift linkage off to get the bracket out of the way even more.

The snap ring on mine was set an angle that made it difficult to get the snap ring pliers on it. I made a trip into town and bought some miniature snap ring pliers which allowed me to move the ring enough to get the big pliers on the ring so I could remove it.

I brushed the snot out of the recess with a small bronze brush where the plug resides and doused it thoroughly with penetrating oil. I used a small pair of slip joint pliers on the nub on the plug and wiggled and tugged on it until it came out. Some ATF came out, maybe 2-3 ounces? Very little anyway.

As has been mentioned previously, some pressure must be exerted on the plug to seat the snap ring. I ran a screwdriver around the edge of the ring to ensure it was fully seated. It wasn't. Now it is.

If I had been a better "rust" mechanic, this job wouldn't have been too bad. I wouldn't rate it as "easy" but it is doable obviously. As usual, having the right tools makes a big difference.

I am hoping I remember the tricks I learned today on my next encounter with rusty bolts.

I haven't driven the rig yet. I am resting my 66 y/o bones a bit.

If you see a mushroom cloud on the horizon, you know the test drive didn't go so well.

 

[NETim]

Initial test complete. 25 mile round trip run to A&W for a celebatory root beer float.

75* air temp. Transmission hit 145* on the way home, running 70MPH. Heavy load (wife's purse.) That's the highest temp I saw.

Truck is stock. Shutters in place and 203* t-stat.

Truck won't get a real workout until next month's trip to Canada through the wilds of the Dakotas. It'll be pulling the boat, equipment and wife's purse.

Probably do a drain n' fill in the next few months.

 

[Missouri2016]

I have been following this thread for a couple of weeks and wanted to post what I have experienced. I have 2016 1500 Laramie that I bought new in 2017. Had issues with the original transmission doing the hard bump from 2-1 gear in 2019. After a year of back and forth with the dealer, they finally replaced after I started a claim with FCA. It shifts great but 2 weeks ago coming back from the lake, we noticed a high pitch whining on the highway when it downshifted and the trans temp was almost 240 F. It shifted fine and as soon as I got off the highway, the trans temp was down to 185. Driving it back and forth to work doesn't get it hot enough, so I drove for about 30 minutes on the highway(without the trailer) and it got up to 225 F. Again, as soon as I got off the highway, back down to cooler temps. After reading your posts, I went ahead and bought a new Heater assembly from the dealer and installed it($173.00) The dealer was kind of a **** about installing it($704.00 installed BTW) and they couldn't get to it for 3 weeks. Took me probably about 6 hours to do it, plus refilling the coolant level and trans fill procedure. I also installed a new factory thermostat and added new coolant. Took it out Saturday, and it ran 185 the whole time and coolant temps were 204-215 and no whining. Next, I removed all but the upper and lower shutters, and the coolant temp never got over 208.
Here's the interesting part:
Running down the highway (no trailer) at 75 MPH and no A/C running, the trans temp crept up to 193. I turned on the A/C, which kicked on the electric fan, and the temp dropped right back to 186-188 the whole time. I wonder if the A/C fan sitting idle disrupts the airflow and that's why it cools down when its on. You would think though that at 75 MPH there would be more than enough flow.
Question: By switching to a lower thermostat(180°) will it throw a CEL? All stock now and no tuner. Also, I'm not sure if I'll put one of caulk04's bypass valves in, but I would like to purchase one.
BTW, that heating unit was a b***h to remove. Spring clamps on the coolant hoses were tough to get at, and the trans fittings did not want to release, even with the correct tool. I wound up just pulling the e-clips with a screwdriver. Installation was easy.

UPDATE:
Finally got some time to take the truck out on Sunday towing our boat(Approximately 5,200 lbs.) and trans temp never got over 185. Ran about 60 miles and most time it was 179 -180 and no whining.
Outside temp was 94F with 45% humidity. I have the bypass valve now, so if I have any trouble in the future I'll switch it out. I have a lifetime warranty through the dealer, so I'm not messing with it right now. These forums are a life saver. Trying to interact with the dealer anymore has become a nightmare.

 

[duktor]

Hello all,
What’s the easiest way to remove hoses on top of the thermostat?

 

[Missouri2016]

Hello all,
What’s the easiest way to remove hoses on top of the thermostat?

That was the worst part of the job. Tried and tried with pliers( 2 hours) but not enough room. I bought a tool(see attached) and that's how I got it. Going back together was easy because I used worm drive clamps. I also bought the c-clip tool for the transmission lines, but you really don't need it if you have a new Thermal heating unit. It comes with new clips. Just pry the old clips out and the lines slide right out.