17 ram 6.4 hd trans overheating

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Mattera350

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Sorry to hear that. I hope it is quickly resolved for you.

Took the truck for a test drive after filling the trans up yet again within 20 min trans light came on running at 220. Thinking the cooler isn’t cooling so well will be towed to the dealer today
 

ripping r

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Took the truck for a test drive after filling the trans up yet again within 20 min trans light came on running at 220. Thinking the cooler isn’t cooling so well will be towed to the dealer today
Hope they get you fixed up. i checked mine this morning 2005 miles was 3/4 quart low. i should have checked it before leaving the dealer. now im checking everything else.
 

HammerHead

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Took the truck for a test drive after filling the trans up yet again within 20 min trans light came on running at 220. Thinking the cooler isn’t cooling so well will be towed to the dealer today
Do you have Lemon Laws in your state?
 

Megazor

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Took the truck for a test drive after filling the trans up yet again within 20 min trans light came on running at 220. Thinking the cooler isn’t cooling so well will be towed to the dealer today

The worst I have seen was 206 yesterday morning. Is it 220 when the temp light comes on?
 

GsRAM

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Wow, sorry to hear about these issues guys. Even when towing my 6k TT loaded heavy, I've never had a trans temp much over 170 degrees. Most times in the 160s even when towing.

Trans temps on a 2500 with the aux coolers these trucks have? Something has got to be wrong. I hope they get it fixed for you!
 

Bob Macknight

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Does the 66RFE have a trans cooler thermal bypass valve(thermostat) like the 68RFE? If so, this may be the culprit for some of you. There have been a few people in the Cummins forums with bypass valves that were not operating correctly and they were seeing temps like this. Most of them just removed it since it is mainly their to get the trans fluid up to temp quicker in colder weather and nothing more.
yes the 6.4 with the 66RFE does in fact at least on mine have that valve
 

bdc2

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Mine will sacrifice oil temp to keep the transmission temp in that 170 degree range. Appears that way anyway.
 

Iron Outlaw

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Mine always read 168 before my rebuild. Coming down to daytona yesterday running 80+ in 6th it got up to 174 a couple of times. Never had a light come on or anything. Thinking of adding a better cooler.
 

68PowerWagon

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Sounds like that bypass valve is stuck closed. My valve wasn't stuck closed, but even wide open it restricts the flow by like 60%. After removing mine my temps are 30-40* cooler. It is a dumb design. Truck shifts fine when cold so I am not sure why they did it. Now our shop truck (08' Chevy 2500) shifts like crap until it gets warmed up. Personally I would rather have stiff shifts for the first 5 minutes over having my tranny run too hot.
 

SouthTexan

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The TBV is mainly used to get the fluid hot enough in very cold areas and for better fuel mileage. The fluid will not get up to temp in very cold sub zero locations. Cold trans fluid is thicker and therefore requires more power from the engine to move it. This is what I was told on the Cummins forum by a FCA US transmission engineer.

You don't want the fluid too cold and you don't want it too hot. There is nothing wrong with the fluid being between 130F-190F. Even low 200F is fine, but remember that the hotter it gets, the quicker it breaks down and needs to be changed. Transmission life is also reduced the hotter it gets because the heat stresses out the clutch packs (heat warp) and other internals.

I mainly did this mod to remove a failure point in the transmission. It does not get cold enough where I live to warrant a TBV and I don't want to stick closed while towing a trailer miles away from home. People have to realize that these trucks are made for thousands of different uses in many different weather conditions. One person who lives in the southern states may not need a TBV valve, but it was put on the truck for those that live in colder climates. Some may think that removing it is unnecessary while others may just want to remove a failure point or need to keep their trans cooler because they tow in 90F+ temps more often.
 

62Blazer

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Kind of surprised of people talking about the trans overheating in the low 170-180 degree range. I'm still catching up on my Dodge...sorry, Ram...facts. In all my previous years of automotive experience I never got concerned until the trans got up into the 200 degree mark and stayed there for any extended period of time, and would expect the normal operating temp to be in the 170-180 range. Generally expect the trans to run close to the engine temperature since it was pretty common for the trans cooler to be built into the engine radiator, and then maybe an small auxiliary trans cooler on top of that. Guess I need to see how mine is setup (2016 that I bought 7 months ago). I know on my last Chevy which was an '03 2500HD the trans would would run in the 190 degree range when towing consistently, and that truck had 150k miles on it and still shifted great when I got rid of it.
 

crazy jerry

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66rfe runs at 170 unloaded. engine 210 but it may fluctuate a hair. oil 225
 

6.4LMegaMan

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I towed my boat last weekend up some 10-13% grades over 2 to 3 mile stretches and never had the transmission temp go over about 174deg, although I did see the oil temp peak around 254deg. Coolant stayed in low 200s. I was surprised how hot the oil got but how cool the coolant and tranny stayed.

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