Transmission temp

[Red Rex]

2018 66RFE behind a 6.4L in a Tradesman 2500.

What should my transmission fluid temperature be towing 6500 lbs (load + trailer wt) @ 65 mph in 90 degree Heat in moderately rolling hill country?

What temp would the danger zone for the transmission?

 

[62Blazer]

It should run about the same temperature when driving with no trailer. The cooling system should have enough capacity to keep it cool under the relatively light load.

In any case, the trans temp often runs about the same as the engine temp. That is because the trans cooler is either built in or mounted on the engine radiator, so it will want to run the same temp. That means up around 200 F. I wouldn't be worried about short hikes up to maybe 220-230 so, and would expect that to only maybe happen on hill climbs for something and come back down. I would worry if I saw 240-250 F........don't think a very short time would cause an issue but wouldn't want any sustained times at that temp.

 

[caulk04]

IMO, I'd start paying attention if it got 30ºF above normal operating temp. You usually cruise around 160 I'd bet?

All in all though, not worried about any oils seeing 220 for a bit, beyond that I'm going to be trying to settle it down.

 

[zeddy]

Get the ATS thermal bypass. I installed it on mine. Highest temp ive been was 165 when the truck was idling 110 degree weather. Before the thermal bypass, same scenario got up to 205. Towing in 95 degree this weekend got up to 150. normal driving is around 140. I heard the 66rfe/68rfe hates heat. i installed it when i changed the trans oil/filter.

thermal bypass

 

[06 Dodge]

Get the ATS thermal bypass. I installed it on mine. Highest temp ive been was 165 when the truck was idling 110 degree weather. Before the thermal bypass, same scenario got up to 205. Towing in 95 degree this weekend got up to 150. normal driving is around 140. I heard the 66rfe/68rfe hates heat. i installed it when i changed the trans oil/filter.

thermal bypass

Wow surprised to hear it works well as such low temps, my 2005 would not shift in to OD when cold, cold as in it was around 45 degrees outside , being the 05 was bought brand new with 12 miles on the OD, I took it in to see if it was normal, was told its normal that it had to be 140 minimum before it would shift into OD

 

[HEMIMANN]

I wrote a treatise about this a while back.

Oil oxidation (any hydrocarbon oil) doubles every 18 degrees F above 140 degrees F. Hence, OCi needs to be halved for operating higher than this. It is not "normal" to run transmission oil above 160 degrees F, and never was until the design geniuses added tiny thermostats and restrictive flow orifices to the oil coolers - all to allow the oil to warm faster for infinitesimal mileage increases.

Many of us took out these thermostats and added a more free-flowing valve block in it's place. I don't get above 165F towing heavy on hot days. Exactly as it should be and always was.

Are tranny's sluggish during winter? Sure. Who TF cares? Nobody cared prior to about year 2010 or so.

 

[Wild one]

Wow surprised to hear it works well as such low temps, my 2005 would not shift in to OD when cold, cold as in it was around 45 degrees outside , being the 05 was bought brand new with 12 miles on the OD, I took it in to see if it was normal, was told its normal that it had to be 140 minimum before it would shift into OD

That was in the programming wasn't the transmission itself.If the outdoor temp sensor was reading temps under 0F the transmission was programmed not to shift into overdrive.There was a big stink about Dodges stupid cold weather transmission programming,that relied on the outdoor temp sensor reading and not the transmissions actual temp.At -40 they would not shift into overdrive no matter what temp the transmission was at.

 

[bglz42]

Just returned from a 3200 mile trip around Colorado. Pulling a 4k bumper pull, bed full of gear. Up and down several 11-14k passes, 90-95 degree heat. (Normal trans temp driving around the Texas Hill Country is 165.) In Colorado, I never got above 170. I have a 2018 6.4l with the 6-speed.

 

[mildrider]

2018, 3500, 6.4 Hemi, pulling a 8k bumper pull camper. I have never had a trans temp above 165.

 

[pjtj2k]

I tow a travel trailer all over the US. My tranny temp sticks right at 178 - 170. This is on the 8 speed behind the 6.4

 

[DanEddy]

I may depend on if you have a gas-powered truck or Diesel?? The trans has a thermostat in the trans cooling lines to the trans cooler. On my Diesel that's set at 168 degrees and for the most part that works OK when unloaded and not pulling hills or mountains. However, when towing my 5th wheel up hills or in the Sierra Mountains it would get up more than was comfortable with. I removed the factory thermostatic block and installed a bypass block and also installed an inline B&M fin style cooler with a thermostatic fan combo on it. Now it runs cooler and although it does heat up more on mountain trips it's nowhere near as hot as the factory stock set up let it get up to.

Heat is the killer for transmissions so having it run cooler is key to longer life. I will say that if you live in snow country where you have extra cold winters days you may need to do something else as the trans does need to have some heat.

 

[Red Rex]

My truck ran well pulling that 8k load. I never did check the temps.


last time I pulled 3 k on the interstate it ran about in the summer at 90 degrees outside

 

[Gary Fields]

Last month I towed a car carrier trailer with a Tacoma on it from Denver to south of Dallas. The trailer and truck was about 6200. Route was all Interstate with rolling hills in CO,KS,OK, and TX with temps over 90 all day. Trans (ZF) never got above 190. Most of the time was at 180. I found driving at about 67MPH was best, seemed like a sweetspot to travel at. Even got 13 or 14 MPG.

 

[Dusty]

I've seen mine creep above 200F a few times but that was on long drives in high temp summer heat towing 7000lbs. up hills. But on the flats at speed limit it's usually 180-190+.
Regards,
Dusty
2019 Ram 1500 Billet Silver Laramie Quad Cab 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33-gallon fuel tank, 18” wheels. Build Date: 3 June 2018. Now at 136933 miles.