Hot Transmission

[Jeepskiy]

I was able to get a hold of powertrain developing team engineers and was told that the mopar 8&9 speed atf starts breaking down at 240 degrees.

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[blnewt]

@JeepCares YOU NEED TO READ THE POST. EVEN ZF Manufacture of the transmission is saying there is a problem with the transmission heaters and the Part has been updated. you need to open a ticket with the dealership to have this replaced. anything higher that 240 typically grenades an automatic transmission. this is simply known logic for 40+years! IMO 220/230 is way to hot even for towing. I Have had many trucks including my 1976 GMC towing my boat and have never seen over 210 degrees. with outside air temps reaching 110-120 degrees not including asphalt temps into the 150-180 degrees. AGAIN 240degrees IS TO HOT. plus your statement says IF EQUIPPED. Doesnt mean its set to the correct safe Temp either. Jeep is failing on the AUTO trans

I was able to get a hold of powertrain developing team engineers and was told that the mopar 8&9 speed atf starts breaking down at 240 degrees.

Yeah, even when 4 wheeling and the coolant is in the 240+ range our AT temp was never over 210. Good to be aware of this issue and will monitor the AT temp more often when running the Jeep hard. Seems like a simple enough fix if that part is the culprit, very valuable info in this thread!

 

[Heimkehr]

I was able to get a hold of powertrain developing team engineers and was told that the mopar 8&9 speed ATF starts breaking down at 240 degrees.

Just so. That's why, when towing, I periodically toggle between the transmission temperature and the oil temperature display data on the central TFT screen. Both fluids are being asked to put in extra shift work, so to speak.

 

[roaniecowpony]

I was able to get a hold of powertrain developing team engineers and was told that the mopar 8&9 speed atf starts breaking down at 240 degrees.

That sounds reasonable. One reference was posted on an RV forum about GM Dexron 6 where the GM techs stated that 270F and above would degrade the fluid. But also that such temperatures degrade seals and other things in the transmission. I'm also betting fluid breakdown is not a completely binary thing. But I'll grant that it is probably an ever steeper drop in service life of the fluid as you increase temperature of fluid past the temperature area you mentioned.
Max Chevy Trans Temperature - Forest River Forums

 

[Jeepskiy]

That sounds reasonable. One reference was posted on an RV forum about GM Dexron 6 where the GM techs stated that 270F and above would degrade the fluid. But also that such temperatures degrade seals and other things in the transmission. I'm also betting fluid breakdown is not a completely binary thing. But I'll grant that it is probably an ever steeper drop in service life of the fluid as you increase temperature of fluid past the temperature area you mentioned.
Max Chevy Trans Temperature - Forest River Forums

Yeah, makes sense to me. Mine lasted 17k miles of running constantly at 240, with couple times hitting 250 on hot summer days or towing a small camper. I would pull over, let it cool down and then repeat.

 

[TaiMc]

Yeah, even when 4 wheeling and the coolant is in the 240+ range our AT temp was never over 210. Good to be aware of this issue and will monitor the AT temp more often when running the Jeep hard. Seems like a simple enough fix if that part is the culprit, very valuable info in this thread!

Indeed! That’s why i have it bookmarked! I’ve been watching my Coolant temp display since I received my jeep back. I’ll pay more closely to the Trans temp and likely will just order that part to have it handy.

 

[TaiMc]

So I ended up ordering and installing new transmission heater for the jeep, mopar part 68485460AB.

Apparently for "some" reason Part #68485460AB is replacing part #68233384AB ….


https://www.moparpartsinc.com/p/jeep__Wrangler/HEATER-TRANSMISSION/94853043/68485460AB.html

Dang, i went on the site and put in my jeep info and it shows the original heater price of $284…and that’s discounted. That’s the one that needs to be replaced if my trans starts to run hot correct?

 

[CarbonSteel]

The transmission fluid (either ZF Lifeguard 8 or Mopar 8&9) has a semi-synthetic base oil and while 240°F is certainly not optimum, it is far from the point of the oil breaking down.

We also have to realize it must be sustained temperatures and not just sporadic for it to become a concern.

Given internet amplification these days, if the 850RE was that failure prone, we would have heard about it ad nauseam...

 

[blnewt]

The transmission fluid (either ZF Lifeguard 8 or Mopar 8&9) has a semi- synthetic base oil and while 240°F is certainly not optimum, it is far from the point of the oil breaking down.

We also have to realize it must be sustained temperatures and not just sporadic for it to become a concern.

Given internet amplification these days, if the 850RE was that failure prone, we would have heard about it ad nauseam...

Luckily the ZF8AT and the Pentastar V6 are both very high on the list of reliable motors/transmissions

 

[AMT]

How would one determine if they have the older heater version with the thermostatic bypass valve? Have a 2021 JLUR.
Also, I do monitor the engine temps in the dash regularly, but what ware the ideal operating temps for coolant, transmission, oil, etc.?

 

[roaniecowpony]

How would one determine if they have the older heater version with the bypass valve? Have a 2021 JLUR.
Also, I do monitor the engine temps in the dash regularly, but what ware the ideal operating temps for coolant, transmission, oil, etc.?

Look at the heater assembly valve body. If it has a round boss cast onto the body, with a plug and snap ring, it is the old heater assembly.

 

[AMT]

Look at the heater assembly valve body. If it has a round boss cast onto the body, with a plug and snap ring, it is the old heater assembly.

Thanks Roanie, not being mechanically inclined (but trying to learn since I got my Jeep) where-ish, approximately, would it be located? (see photo)

 

[roaniecowpony]

The part is located on the side near the bottom of the transmission next to the driveshaft.

Here is the new heater. Note there is no boss on the casting to contain the thermostat. Also, the heat exchanger itself, will have the part number 68485460AB

 

[TaiMc]

The part is located on the side near the bottom of the transmission next to the driveshaft.

Here is the new heater. Note there is no boss on the casting to contain the thermostat. Also, the heat exchanger itself, will have the part number 68485460AB

Thanks for answering my question. ??

 

[RubyRecon]

Is there a TSB for this part? My 2020 JLUR runs at 240+ all the time. No help from the dealer. I ever asked if I could pay to have the fluid changed and was told if is lifetime and not serviced. Of course I told them that at these high temps “lifetime” would be here sooner than later. No help. No love.

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