ZF 8hp70

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Groppelt

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I know this has been asked before. I have a 2014 with the 8speed transmission and 5.7. Transmission is always at about 195 degrees. If I get stuck in traffic it goes up to 220 degrees. I was towing my 7000# camper and after an hour check engine light came on and temp was at 260. Brought it to the dealer and they said " sealed for life" and they didn't do anything. Service rep actually told me if I'm towing 7000# I should have a 2500! Doesn't seem right to me. Anyone have similar issue or any idea?
 
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Groppelt

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Thank you. That's what I was thinking also. Truck has 139k on it now. This happened at about 130k. I guess I'll have to go to a local transmission guy since the dealer won't do anything.
 

crash68

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We're you using to Tow/Haul mode? Did the temperature creep up that high or did it spike quickly? There might be a problem with the thermal management unit on the side of the transmission. It warms and controls the transmission cooling, the actual cooling is the top several rows of what also the AC condenser.
There's actually a bypass kit for the 8HP TMU, there's a thread on this forum somewhere (I think @Wild one started it)
 
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Groppelt

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Yes. I was in Tow/Haul mode. Temp crept up over about 20 minutes. I was pushing it. About 70mph and climbing hills but ever since it seems to be hot all the time. I might have the valve changed as well as a filter and fluid change. Not really sure if I want to go with the block off plate. Do you know if that would generate a check engine light?
 

regal81455

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Hope you have your heart attack preparedness kit made up... that fluid change will run you $700+/- unless you're willing to do yourself and even then it's $$$. I know I just about **** the brick when I was looking into it for my 16'.
 

grizzstang

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Unfortunately you can't just buy the thermostat, you have to buy the whole heater assembly.

There is a member on here that builds his own thermostat plug that functions as if the thermostat is open fully all the time.

It is a nice unit and cheap. I bought one but have not put it in yet. If I was in your shoes I would get one and put it in to see if that solves the overheating issue.

If it does you can figure out if you want to replace the whole unit or continue with the thermostat plug.

You can look through here.

https://www.ramforum.com/threads/8hp70-heater-bypass.172998/
 

crash68

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I might have the valve changed as well as a filter and fluid change. Not really sure if I want to go with the block off plate. Do you know if that would generate a check engine light?
The TMU comes as a complete assembly, you can't get just the OEM thermostat bypass. I don't recall anyone reporting an check engine light because of the aftermarket bypass but I'm not sure if it's been in really cold weather.
I found that thread on the bypass kit: https://www.ramforum.com/threads/revmax-8-speed-thermostat-bypass.171776/
Another thread on the subject: https://www.ramforum.com/threads/8hp70-heater-bypass.172998/
 

6.7CumminsDrvr

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My trans stays around 189-195, I’ve seen it hit 205 when I was beating the **** out of it climbing a grade loaded to the gills.......my oil temps go WAY higher than my trans ever does.

I am running 180 thermostat so my radiator may not have as much heat soak compared to someone running stock.
 
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Groppelt

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Thanks for all the advice. I knew the fluid was expensive. I will probably go ahead with the fluid and the bypass/heater unit. Going to try to find a local transmission guy that can do the work. I'll post back and let everyone know how it worked out. Thanks again!
 

MRFREEZE57

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Hope you have your heart attack preparedness kit made up... that fluid change will run you $700+/- unless you're willing to do yourself and even then it's $$$. I know I just about **** the brick when I was looking into it for my 16'.

if you can DIY a lot of money can be saved by going with another brand of fluid besides the Mopar stuff. I used Redline D6 (which is less than half the cost of the Mopar) replace the plastic pan with a PPE pan, drained and refilled 3 times for under 400 bucks.
 

PoMansRam

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if you can DIY a lot of money can be saved by going with another brand of fluid besides the Mopar stuff. I used Redline D6 (which is less than half the cost of the Mopar) replace the plastic pan with a PPE pan, drained and refilled 3 times for under 400 bucks.

For sure on that.

Even if you insisted on staying with the OEM fluid after the powertrain warranty is up, you can mail order the mopar 8-9 speed fluid for under $200 for 10 quarts. Not sure how/where the super high cost quotes are coming from.
 

regal81455

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Fluid = $200
Pan/filter = $100
My time = $200 ATLEAST
--------------------
That's $500

Dealership and trusted garage wanted $700 +/-.

Not saying it can't be done for less just saying it's not the same as the old TH350 / 400's of yesteryear - used to be $30 for fluid and $30 for filter. Where you used to be able to HAVE done for under $100 all day long.
 

GsRAM

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Fluid = $200
Pan/filter = $100
My time = $200 ATLEAST
--------------------
That's $500

Dealership and trusted garage wanted $700 +/-.

Not saying it can't be done for less just saying it's not the same as the old TH350 / 400's of yesteryear - used to be $30 for fluid and $30 for filter. Where you used to be able to HAVE done for under $100 all day long.


True, but doing it yourself is still less than half the cost, (I dont figure my labor in the work I do on my own stuff) a substantial savings if one is competent to do it correctly (as you said, not easy with the 8 speed)
 

regal81455

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True, but doing it yourself is still less than half the cost, (I dont figure my labor in the work I do on my own stuff) a substantial savings if one is competent to do it correctly (as you said, not easy with the 8 speed)

For the most part I do all my own work too and generally speaking I don't really think about a dollar value for my time either but when discussing this it probably should be considered when figuring why it costs what it does from a shop point of view. That's just the commercial industrial GC in me though - always looking at the cost / value of something.
 

GsRAM

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It's a valid viewpoint no doubt.
 

Ram_Bobby

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What about an additional trans fluid cooler?

Also, I don't mean to bust on the original poster, but could it be 70 MPH up hill with a 7K pound camper might be too much? I don't regularly tow, but when I do, set the cruise on like 65MPH, just stay in the right lane and keep the screen on the trans temp constantly.

Was the trailer 7K before loading it? Might have been pulling more? Just some thoughts.
 

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