Engine and trans running hot

[*tim*]

A week ago i went on a long trip and on the way home i seen the trans was about 220. It slowly crept up to 240 and started shifting very hard so i pulled over and let it cool off. After that it shifted fine but after 30-45 mins of 75-80mph it crept back over 200 and kept climbing. I limped it home and over the last week it does fine around town but the engine is running about 220 and the trans about 195-200. Previously the engine never got above 210 and the trans never got above 190.

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[NJMOPAR]

Don't know your year, maybe the active shutters staying closed?
Electric fans working? T-stat stuck?
You could pop in a 190 or 180 stat, the factory one is 203.

 

[crash68]

If you have the 8spd transmission, you probably need a new Thermal Management Unit. That does double duty as it heats the trans fluid when it's cold and bypasses the fluid to the cooler which is the top couple of rows of what's also the AC condenser. The bypass valve built into the TMU is not replaceable.

 

[*tim*]

If you have the 8spd transmission, you probably need a new Thermal Management Unit. That does double duty as it heats the trans fluid when it's cold and bypasses the fluid to the cooler which is the top couple of rows of what's also the AC condenser. The bypass valve built into the TMU is not replaceable.

That wouldn't make the engine run hot though would it?


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[crash68]

That wouldn't make the engine run hot though would it?

It wouldn't cause the engine to run warm, but even if the coolant is hot the trans should stay cool.
Even towing 8K lbs my trans doesn't wander over 200°F even with 220°F coolant. Granted mine is an EcoD but the Hemi uses the same transmission/cooler set up.

 

[*tim*]

Well ive flushed the radiator, put a 180 deg thermostat in and also removed the active grill shutters. The engine is still running 10-12 degrees over the thermostat temp and the transmission still gets just as hot also. The transmission cooler and lines are getting hot so its pumping fluid fine. Im thinking something in the transmission is generating excessive heat

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[Wild one]

Well ive flushed the radiator, put a 180 deg thermostat in and also removed the active grill shutters. The engine is still running 10-12 degrees over the thermostat temp and the transmission still gets just as hot also. The transmission cooler and lines are getting hot so its pumping fluid fine. Im thinking something in the transmission is generating excessive heat

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If you have the grill shutters it means you have the 8 speed.The heater unit on the side of the 8 speed has been known to give trouble,it's not a common issue,but it might be going south on your truck.It also contains the transmissions thermostat,but the thermostat is non-serviceable in the bottom of it.They aren't all that expensive or that hard to replace,but you'll need to top up the 8 speeds fluid level if you do change it.Would be a good time to service your 8 speed while you're at it

 

[chrisbh17]

Well ive flushed the radiator, put a 180 deg thermostat in and also removed the active grill shutters. The engine is still running 10-12 degrees over the thermostat temp and the transmission still gets just as hot also. The transmission cooler and lines are getting hot so its pumping fluid fine. Im thinking something in the transmission is generating excessive heat

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Like wildone said I would look at the thermal unit on the trans.

It can allow fluid through, like you felt, but it basically modulates how much gets through, how much is cooled, etc. So it still could be defective enough to cause an issue even while letting some fluid through.

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[*tim*]

If the cooler and return line were significantly colder that the line from the transmission i could see it being the thermostat but both the cooler and return line were almost as hot as the main line so that tells me there is plenty of flow and an excessive amount of heat being generated. Im not trying to ignore your guys opinions but just throwing around ideas before i spend any more money on it.

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[scott lass 18]

I had 195 stat just went with 180 and on hot 101 day here it all ran cooler trains oil engine like 186 to 191 so see all running better years back couldn't get 180 suck but good all summer also have ac fan to run all the time at 190 and up cool today so at 183 now 75 out ! ow did change trainsmission amsiol train s oil at 40,000 ran better for me !

 

[chrisbh17]

If the cooler and return line were significantly colder that the line from the transmission i could see it being the thermostat but both the cooler and return line were almost as hot as the main line so that tells me there is plenty of flow and an excessive amount of heat being generated. Im not trying to ignore your guys opinions but just throwing around ideas before i spend any more money on it.

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If you are sure there is no air left from changing the coolant, I would think about changing the trans fluid next. If it is the 8 speed its a pretty specific process....there are a few how-tos on the forum here.

The thermal management unit on the trans, BTW, isnt an "all or nothing" type deal. Its supposed to modulate flow in and out of the cooling circuit, so right now it could even be stuck on "full open" or somewhere in between, and throwing off the WHOLE coolant circuit (including main coolant temp).

 

[Wild one]

If the cooler and return line were significantly colder that the line from the transmission i could see it being the thermostat but both the cooler and return line were almost as hot as the main line so that tells me there is plenty of flow and an excessive amount of heat being generated. Im not trying to ignore your guys opinions but just throwing around ideas before i spend any more money on it.

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If the trannies healthy,there's only 2 things making it run hot,one is the thermal bypass valve on the pass side frame rail,the other is the transmissions heater assembly on the side of the tranny,it's been suggested you try changing them,and you don't seem to like either suggestion,so i'm not sure what else you think we can suggest to you,other then take it to a dealer and let them have it .Throw a high flow Milodon thermostat in the engine and see if that helps. By chance you didn't top up the anti-freeze lately did you,they are very specific about using the proper anti-freeze,as you shouldn't just throw good old green anti-freeze in from the local gas station.

 

[Wild one]

https://www.summitracing.com/parts/mil-16406

 

[*tim*]

If the trannies healthy,there's only 2 things making it run hot,one is the thermal bypass valve on the pass side frame rail,the other is the transmissions heater assembly on the side of the tranny,it's been suggested you try changing them,and you don't seem to like either suggestion,so i'm not sure what else you think we can suggest to you,other then take it to a dealer and let them have it .Throw a high flow Milodon thermostat in the engine and see if that helps. By chance you didn't top up the anti-freeze lately did you,they are very specific about using the proper anti-freeze,as you shouldn't just throw good old green anti-freeze in from the local gas station.

I am concerned about the health of the transmission. The transmission downshifting hard while running hot but within operating range tells me something is wrong internally. I ordered some fluid so i can check the level. If thats not the issue it will probably go to the dealer. I just know they will not be able to replicate the issue and tell me to drive it until it fails.

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[chrisbh17]

I am concerned about the health of the transmission. The transmission downshifting hard while running hot but within operating range tells me something is wrong internally. I ordered some fluid so i can check the level. If thats not the issue it will probably go to the dealer. I just know they will not be able to replicate the issue and tell me to drive it until it fails.

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FWIW there are several people on this forum that have had clunkiness, slipping, etc when the 8 speed is running hot. Doesnt mean the trans is toast, at least not right away. IIRC most of them did have issues with the thermal unit(s), but they were only resolved with a replacement trans (because dealers are 100% convinced you cannot replace just the thermal unit(s) on the trans...I think FCA pretty much tells them not to touch the trans at all)

 

[Wild one]

FWIW there are several people on this forum that have had clunkiness, slipping, etc when the 8 speed is running hot. Doesnt mean the trans is toast, at least not right away. IIRC most of them did have issues with the thermal unit(s), but they were only resolved with a replacement trans (because dealers are 100% convinced you cannot replace just the thermal unit(s) on the trans...I think FCA pretty much tells them not to touch the trans at all)

The thermal units including the heater don't come with a replacement tranny,they have to be bought separately if you want them replaced with a new transmission. At least they never came with the new transmission I bought

 

[*tim*]

Well i replaced the 3 way valve just because it was cheaper and easier to change out. It does seem to help though. However its been cold and raining lately so i need a hot day to get on the highway and cruise for a while. I also picked up some fluid so i can check the level if i get some time

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[*tim*]

Does anyone know what direction rhe coolant flows in these trucks? Im assuming the upper hose to the lower hose?

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[*tim*]

The transmission and engine were still both running hot so i replaced the heater on the side of the transmission. Now the engine gets to temperature and holds at 185(180 thermostat) but once the transmission gets to temperature the engine runs hot, clear up past 200 even on the highway. The transmission does hold under 190 now even when driving the truck hard.

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[Tim Garceau]

You need to turn the supplemental fan on earlier, when tuned and mechanical fan deleted it is cycled on at 196.x degrees. The air conditioning button will turn it on earlier, but factory electric fan is ~223 when the PCM will start pulling more timing.

200 degrees is not concerning especially with being the middle of summer. Yes, flow is high to low through the radiator so your temperature reading at the thermostat is the hottest point in the system.