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Transmission warmer

27K views 68 replies 23 participants last post by  Bounty Hunter 
#1 ·
Hey guys,

Does anybody know the reason of the transmission warmer that's on the driver side, rear engine beginning of transmission (don't recall the exact location). There are 2 coolant lines going in, probably one inlet and one outlet, and 2 transmission lines.

The reason of the question is because I see constantly a 20-ish degrees difference between coolant and transmission, and this is without any towing. I'm thinking to install a valve to limit the coolant flow through that heater, but first, I'd like to understand why dodge engineers would like such a hot transmission fluid.
 
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#2 ·
It's a thermal management unit, from what I understand its purpose in life is to warm the tranny fluid quicker in order to make it more efficient and improve fuel economy. If you would like more info google "ZF Thermal Management Unit"

Cheers,
 
#4 ·
Thanks. What puzzles me is why would they want such a hot transmission? I can see that fluid doing 200F + easily while towing.

Anybody tried to take it out or to put a valve to reduce its operation? I was thinking to add a bypass valve (electric or cable operated) that can be opened, closed, or in between.
 
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#7 ·
After sfraser explained in the previous post about the transmission management, I read few things online, and it seems Chrysler implemented this also due to some hefty carbon credits they got, since epa was all super excited. So I don't think the whole reason was performance, it's gotta have something to do with mileage and making those govt folks happy...

What I'll try to do is to get a bypass valve, 2 inlets and 2 outlets, cable operated and slap it in front of the warmer. I'll post some updates after I'm done with it. The idea is to leave it fully open, so transmission heats up to 160-ish,then close it to fully bypass the warmer. Maybe open it a bit during the winter.
 
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#5 ·
See if anyone chimes in but after i had my TMU replaced tran temps are always below 200 towing or not.
 
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#6 · (Edited)
I wouldn't favor shade tree mechanic ideas over those of design engineers. If they thought that the transmission didn't need a warmer, it wouldn't be there and they would have saved a lot of engineering and production costs. And BTW, that system already is a means of controlling the temps. If your truck doesn't have a problem and you drive within the specified operating parameters, you should be fine. We haven't heard of many transmission problems here. :cool:

From my readings, the controller allows fast warm up, reducing wear and improving economy. If you are remembering those charts that show transmission wear increasing exponentially with fluid temps, forget it. Those charts were made before synthetic fluid and modern transmission designs.
 
#8 ·
FWIW, towing my trailer into a 20+ headwind at ~75MPH got me to a new record for my transmission temps... 195 degrees. Unloaded, it ramps up to about 170 really quick, then will be in the 170-180 range from there on out. Even in the winter. The thermal management unit works. Gets up to temp, then switches to the cooler when needed.
 
#10 ·
I am all for modding vehicles, just not ones that are under warranty. Don't claim to be an engineer, don't get paid enough to outguess their logic :)

One of my previous cars was a 1970 Dodge Coronet 383 with a transplant 440 hi PO out of a Dodge Polara Police Car. Did a little modding with that one. It also got about 6 mpg. Of course gas was .59 9/10 too :)
 
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#13 ·
Thanks, I watched all Shawn's videos. The difference is that I still want to use the warmer/efficiency unit, as I can see benefits in raising the temps in cold weather, that's why I need an adjustable valve. I just don't like going over 160 normal driving and 180 towing. Just bypassing it is easy, take the water heaters out and join them together and cap the warmer to stay clean inside.
 
#24 · (Edited)
Howie, I base my statements on "old school" data regarding transmission operating temperature. I do not know this zf transmission and this is why I made the post, to find out if it is worth adding a bypass valve (similar to what cabin warmers have) between water pump and transmission warmer.

On one side we have the engineers stating that 190 is optimum transmission temperature. On the other side we have the carbon credits Chrysler got with this system. I may be a bit paranoid, but I think that Chrysler engineers won't ever say that 190 degrees transmission temperature is too hot, since that statement will go against having the warmer, which would put Chrysler in a bad light since they chose carbon credits and not reliability. It is possible indeed for this zf transmission to have superior clutch packs, that are superior design and materials compared to an older design transmission (like 545rfe for ex) and they can withstand this heat without issues, but I don't know if that's the case, hence my questions. I just want to find out the truth, and not the "politically motivated" truth.

On the other side, I have never, ever heard of, or seen a transmission failing because it was running too cold. The electronics, including the solenoid pack(s) are usually inside transmission, and they definitely do not like 200+ temperatures.

To summarize, I honestly don't know if it is worth adding a bypass valve, or delete the warmer. I find it a bit silly though to warm the transmission fluid to the coolant temperature, and then running it through the front cooler to drop it few degrees. And I see people getting to 200F easily while towing. If the transmission would be designed to operate in 200+ temperature, what's the point of having the transmission cooler? Or at least it should have a thermal bypass valve before the transmission cooler, which, as far as I know (and I may be wrong with this statement) does not exist. I suspect that the current system should last enough to get us out from warranty, but may fail later on. Best would be to get an educated opinion from someone that does know very well this zf 8hp70 transmission that we have.

Oh, another aspect I hate, no dipstick, so pretty much you won't know if the fluid is burned or not, unless you go under the truck and fiddle with the filling port...
 
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#15 ·
Obviously I am interested. My normal operating temperature for my transmission is between 203 and 213 degrees ALL THE TIME. When I tow it gets and runs hotter, sometimes close to 240 degrees. FICA says those temperatures are "normal".

260 degrees is the cut-off that detunes the engine and slows/cools things down. Spoke directly with a ZF technician on that issue also. Same information as from FICA.

Real curious what your modification is and whether it works.
 
#25 ·
By any mean I intend to over engineer things... Just want to have a reliable truck overall. And obviously, the reason of the post was to find out what folks think. Maybe be lucky and get an expert in zf transmission... If there are folks disagreeing, so be it, I won't call those people names, lol. You can't find out the truth if you're not actively seeking it, right?
 
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#18 ·
I had a trans cooler on my 2500, never saw over 165 while towing, never over 135 while not towing. Now this truck has a trans warmer... can't get my head around hot trans fluid, which is never good for a tranny...

Head
 
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#19 ·
It also has a cooler. If i recall the thermal management unit redirects the flow during cold starts so the fluid is warmed by engine coolant. Keep in mind the system is designed to run at 180-200 degrees. This not your transmission from your 1990 pickup truck.
 
#21 ·
My old 2500 was a 2012... but I figured they have it covered just hard to let go of old school thinking...

Head
 
#22 ·
The people in the know seem to think 190F is where it runs best. And the TMU controls to that temp. Both heating and cooling, by allowing the oil to run through the cooler while bypassing the heater. All controlled electronically by the transmission ECU. Why mess with it?


This excerpt from an Allpar.com article on the ZF 8HP transmission

"new thermal management system, designed to quickly raise the transmission fluid temperatures to cut parasitic losses and wear, improving fuel efficiency by 1.7%. It is enabled by an electronic thermostat which constantly monitors antifreeze temperature; once it’s hot enough, warm engine coolant is circulated through a thermal exchange unit which heats up the transmission fluid. In most vehicles, the transmission heats up independently of the engine. (The system also works for engine oil.)

Chrysler’s Dave Sowers said:

We get benefit from bringing both of them [oil and transmission fluid] up to operating temperature faster. The primary benefit comes in the transmission. In colder climates, you could drive a vehicle for hours in the winter and the transmission might never reach that 190° (F) for the most efficient operation. So what we do is use some of that hot engine coolant through the heat exchanger to bring it up to 190° as quickly as possible, and that gives us efficient operation very quickly."
 
#23 ·
only drawback to the warm oil temperature in the winter is reduced heat available to heat the cab. My heater in this truck is much weaker than what I had in my 2000 Laramie with a 5.9 liter gas engine. But then it burned twice as much fuel and didn't warm the transmission nor engine oil with the cooling water.
 
#26 ·
Thermo,

There is a post on this site somewhere where one of the members had oil temperature data from ZF directly. As I recall it (which could be erroneous) ZF was OK with our transmission and their fancy synthetic fluid having occasional spikes up to something like 250 deg F. I'll try and search for it when I get a chance. IF I find it I'll repost it. Someone else here may know where it is too.
 
#28 · (Edited)
Thanks guys, I saw captain's posts, with his transmission warming issues. Granted, after I started the thread. But here is the "problem": on one hand we have Chrysler and zf tech guys saying it is fine, but in the same time they are bound to play by corporate rules. So even if they would have data suggesting that, let's say 170F is way better than 200F, they can't come forward admitting it, since it contradicts corporate data. These days corporations have more lawyers than engineers... On the other hand, we have the "old school" data, which states that optimum temperature for a transmission is at about 160 degrees. I have a hunch that zf's and Chrysler's numbers are made to lead to better fuel economy and not necessarily longevity, but I have no proof so far. And I am not trying to overthink this, just trying to find some unbiased expert opinions.

Even considering the existing data, I think zf stated that the optimal temp is between 176-212F. My goal is to keep the transmission within 175-ish range, which is not possible every time with the current configuration of the transmission. I'll look up some zf manuals, if I cand find any, or even buy them, I'll know more and definitely share the findings. Also, thanks to everyone that chipped in with opinions, I appreciate it.
 
#29 ·
I expect that there must be some kind of proportioning valve that directs coolant to the heater unit. If you could find it, perhaps there would be a way to interrupt the signal too it and stop the heater from heating. Save having to cut lines and put in valves to effectively do the same thing.
 
#30 ·
Absolutely correct. I won't do anything till I fully understand how this transmission works. I wonder if it's the circled bolt in the pic below, it looks to be sealed or having some kind of loctite on the threads. Could be also some sort of flow regulator. I think the fluid goes in the warmer straight from the transmission, and from there it's directed towards the cooler in front.

 
#33 ·
The plug circled is there from the casting process, and is just a plug. That cooler on the side of the trans is used to get the trans up to operating temp fast so as to reduce its internal friction as soon as possible - this is all done to gain fuel economy on the certification cycles.

There is a directional coolant valve controlled by the engine controller, located on the passenger side of the engine compartment on the frame rail next to the alternator. This controls the amount of coolant flow either to the heater core or to the trans cooler. If you're not demanding heat in the cabin, then it directs coolant to the trans oil heat exchanger, else it sends coolant flow to the heater core. During trailer tow it also demands coolant flow to the trans in order to actually absorb heat from the engine since the trans has excess cooling capacity and operates at a low temp during heavy operation.

Most transmissions we've seen both on the Ram and Jeep EcoDiesels operate at 90-100C (195-212F). If you're operating at over 110C (230F) all the time, likely there is a clutch slippage issue in the trans. At 140C the trans depowers and goes into hydraulic default mode (6th gear, converter unlocked). Trying to run the trans cooler will just result in degraded fuel economy. If you want it to do so, just disconnect the coolant lines from the heat exchanger and connect them to one another to bypass it - now it behaves just like the Grand Cherokee.
 
#36 · (Edited)
Thanks gde! Much appreciated.

1. Not to brown nose you at all, but those things you do all the time, without any obligation, made a big contribution of me get the gde tunes (ram and liberty crd). On the top of a quality product, you explain things to us, which is totally outside of the tune per se. This means you guys are not only looking for profit, you have passion in what you do! And this is true value!
2. Do you guys think it is worth to install a bypass valve, which is supposed to adjust the amount of coolant going through the warmer? I am thinking to adapt a conventional heater 4 Way valve, operated by a choke cable, which will allow me to adjust the amount of coolant going towards the transmission warmer. Also, do you think that operating the transmission at 160 would hurt the transmission? I one have never seen, or heard of a transmission failing because it ran too cool. I believe that the temps of this ram transmission are that high solely to reduce fuel consumption in detriment of reliability.

 
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#41 ·
Ok so maybe someone smarter than me can make the way the engineers designed this combo make some sense to me. I drive a 15 CNG Powered Silverado V8 for work. The engine comes up to temp 210* within 2 miles as did the 09 Impala I drove prior to that. Now granted this is a apples to oranges comparison but wouldn't it make more sense to have the engine come up to temp quickly then use excess heat to warm the trans fluid? Seems the engine taking 10 miles +- to get to full operating temp due to excess heat being used elsewhere is hard on the engine and causes it to use more fuel?
 
#42 ·
Seems to me there are a couple things to realize in your apples to orange comparison----perhaps more like apples to grapefruit. Our ecodiesel has ten to 11 quarts of oil to warm up and your comparative vehicles have something like 5 quarts. Probably less than half. Second your ecodiesel is getting something like twice the mileage as your comparison vehicles while doing more work moving a heavy vehicle so it has way less heat to reject to warm the system up. This is a common issue with diesels in cold weather when not working hard. Much less excess heat to reject than a similar gas engine. One of the smarter folks on this forum can probably provide the actual specs of heat to be rejected on a similar sized gas/diesel engine.

All the best,
 
#43 ·
We don't see a clear advantage or disadvantage to the trans running at 160F or 190F. At colder temps it will have more internal friction, so it might take more effort from the engine to turn it. You also might notice more harsh shifts since, ultimately, they're calibrated at standard operating temps of the trans.

It could be said that the "keep it simple" philosophy applies well. The directional valve already installed is useful for its purpose and in our tuning we've already made further changes to optimize it's function in the name of getting the engine up to temp faster.
If you don't want the benefit of the heater, I would just disconnect the coolant lines from it and connect them together. In this way it behaves like the Grand Cherokee without the heater which operates at the same standard temp as the Ram, just takes longer to get there.

If you want the trans to run permanently at a colder temp you'd have to remove it's thermostatic assembly and let fluid flow to the trans cooler all the time.
 
#45 ·
GDE folks, to help clarify your response I would like to ask as follows-if we assume the transmission warming is done by FCA for a variety of possible benefits including, perhaps, EPA mileage testing, shift characteristics, transmission life and whatever other positive things their engineers deemed worth it, do you see a significant detriment to the engine allowing their system to work as designed? If so, what is it? My observation is it seems to limit passenger compartment heat, which I can live with. I am surprised at how quickly the engine and its lube oil and the transmission heats up in low load driving even in minus ten and twenty deg F.

All the best,
 
#44 · (Edited)
Thanks again GDE for your insight into the inner workings of this vehicle. It is ALWAYS valued by me and I'm sure numerous others here.

Personally I prefer the engine get to temp as fast as possible. While I don't mind the trans running at 175*, I would prefer the engine not to have to wait on the trans to get to temp. As stated earlier I think they should have allowed the engine to get to operating temp then used excess heat to warm the trans.
 
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