8spd overheating repairs?

[Shakenbake]

My truck is a 2014 1500 5.7 hemi with the 8spd transmission. I only have 84000 miles on it and the trans was already replaced at around 45000 miles. Driving locally under 45 mph the trans temp runs between 194-197 but once I’m on the highway it only takes about 20 minutes and the trans temp will run between 215-240 and then starts with hard shifting. I just replaced the water pump and thermostat and the 3 way coolant valve. I am thinking the next step is the transmission oil heater. I was looking at the revmax bypass kit to eliminate it but am unsure of the transmission operation in the cold winter months.

 

[PoMansRam]

I see you live in PA, so ambient temps aren't the issue. What does your engine coolant and oil temps settle out at?

Like you say, it sounds like the ATF heater. On both my 2017 and 2019, even on a 90F summer day in Buffalo, I've never seen ATF temp get above maybe 188F? 240F is way too hot. I believe ZF says 250F is the extreme danger zone where the fluid is degraded.

 

[caulk04]

If you're up to looking through this long thread, there's lots of good info. https://www.ramforum.com/threads/8hp70-heater-bypass.172998/

I make a part that does the same thing as revmax's kit for less money, quicker/easier install and totally stock appearance if warranty is of concern.

 

[crazykid1994]

Lots of people can speak for caulks piece. There is actually a thermostatic valve in the transmission heater assembly and it sounds like yours is faulty. If @Wild one comments in he’s in Canada and has his heater removed and as far as I know has had 0 issues driving in the cold.

 

[Wild one]

My truck is a 2014 1500 5.7 hemi with the 8spd transmission. I only have 84000 miles on it and the trans was already replaced at around 45000 miles. Driving locally under 45 mph the trans temp runs between 194-197 but once I’m on the highway it only takes about 20 minutes and the trans temp will run between 215-240 and then starts with hard shifting. I just replaced the water pump and thermostat and the 3 way coolant valve. I am thinking the next step is the transmission oil heater. I was looking at the revmax bypass kit to eliminate it but am unsure of the transmission operation in the cold winter months.

Go for one of Jesse/Caulk 04's thermostat bypasses.It's easy to install,and if you think it's to cold in the winter,it's easy to re-install the stock thermostat back in for cold weather driving. Run Jesse's piece in the summer,and then swap back to the stock thermostat for the winter,if you feel uncomfortable with it's winter operating temps. It's all of a 20 minute job to swap them

 

[crash68]

.I just replaced the water pump and thermostat and the 3 way coolant valve. I am thinking the next step is the transmission oil heater.

The three-way valve does nothing for the cooling transmission temperature. If your transmission temp is spiking high you need to change the thermal management unit on the side of the transmission or use the thermostatic bypass kit mentioned by Wild one

 

[Shakenbake]

My coolant is at 203 and engine oil usually around 215. I most likely will be interested in your kit caulk04

 

[joesstripclub]

If you do go with the Revmax kit I have it installed and I'm in Colorado. Even on the coldest days this past winter I still hit at least 90 degrees on my 9 mile trip to work. I haven't seen over 160 this summer with it installed. Caulk's piece will save you some coin though and get you pretty much the same results.

 

[Shakenbake]

I just installed caulk’s kit today, just have to take it for a test ride now.

 

[Shakenbake]

Everything seems way better now with the new part never hit 150 today on my test run and it’s 91 degrees out today

 

[Glenn Williams]

Thank you for the update shakenbake,

The bypass seems like a great mod. The question I have is what are the dangers of running a cooler/cold tranny?

 

[joesstripclub]

Thank you for the update shakenbake,

The bypass seems like a great mod. The question I have is what are the dangers of running a cooler/cold tranny?

Judging by the other ZF 8-speed installations without a fluid heater, I would say there is no danger. Maybe marginally less mpg. Also fluid will last much longer at lower temps.

 

[Glenn Williams]

Ok thanks

 

[Shakenbake]

It has to be way safer then running at 240 degrees with hard shifts and a whining noise. So I will take cooler over that.