8hp70 heater bypass

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Fritter

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I've had the tranny checked by the dealer twice. The response both times is that the tranny is good and the fluid looks good. Specific questions about the TMU and TBV were given a short answer of "They were OK".

Edit: I am going to be installing caulk04's modified TBV in the next few days and check the AGS. I'll post the results.
 

Wild one

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I've had the tranny checked by the dealer twice. The response both times is that the tranny is good and the fluid looks good. Specific questions about the TMU and TBV were given a short answer of "They were OK".

Edit: I am going to be installing caulk04's modified TBV in the next few days and check the AGS. I'll post the results.
If they pulled the fill plug while it wasn't running,and drained enough fluid to actually check the fluid,you might want to do a fluid level check sooner then later.
 

Daniel Ortiz

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@Fritter , that's some excellent data recording you've done there. Major props. I agree with all your concerns. The biggest concern in my mind is, if the thermal management system uses a heat exchanger between the engine coolant and the transmission oil to heat it up, then a faulty thermostatic valve causing the transmission overheating only makes sense until the transmission oil reaches the temperature of the engine coolant, which for me runs around 222 F at highway speeds, same as you mentioned. But my transmission was up to 230 F and probably climbing (based on others reports of temperatures as high as 260 F) the first time I noticed this problem, which would not be possible from the heat exchanger alone. That leads me to suspect that the transmission is experiencing a source of heating internal to the transmission that is causing those temperature spikes above engine coolant temperatures. A constantly slipping torque converter would seem to fit the bill, or any other device that was supposed to lock up, but didn't, such as the clutches or band brakes. So, that is concerning.

I've bought a replacement thermal management unit and inside it a stock thermostatic valve which I plan to replace mine with, just to test whether the problem is with the valve or not. Unfortunately, I'm also buying a house and working on renting my current house, so there has been no time to play with the truck at all over the last month, and there likely won't be until sometime in late June or early July.

Nevertheless, I'm glad you understand the concerns @Fritter , and I hope you succeed in tracking any potential problems after you install @caulk04 's part.
 

Fritter

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How about overfill? I check the tranny fill level using the instruction set (from the new transmission). Leveled the tranny pan rails using a torpedo level. I started the procedure with tranny at 73 F (step 5). The tranny was at 93 F at step 13 and 102 F when I shut down. About 3/4 qt of excess fluid came out during step 13. Now I'm wondering if I did the procedure correctly.

Edit - approx 28 fl oz removed. Differences could be whether the vehicle was level during the dealer servicing vs tranny pan rail level. The fill hole is higher enabling more fluid in the tranny when following the fill procedure (second case) which should lead to an underfill by the dealer. Also, what is the impact of the cooler on the fill level?

Edit 2 - I assume the tranny pan rail is the interface between the aluminum tranny case and the plastic pan. Please confirm.
 
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Fritter

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My next step was to test with the correct fill, test with the AGS open (pull the fuse), then add the modified TBV. Now my next step is to review this fill.

Daniel - I showed the charts to the dealer and they barely glanced at it. I don't think the techs/mechs actually saw the data, only the customer service representative.
 
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Fritter

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Here's a follow up to post #420 / 421:

In post 425 I stated that ~28 fl oz of excess transmission fluid was removed while following the transmission fluid check provided in this thread (key is the leveling of the tranny pan and pre-test setup). After conducting some test runs to ensure there were no issues (i.e. removing too much fluid) I drove the vehicle on a route that I had previous data on. The results are:
Before fluid check
@ 68 mph: 226F Oil, 217F Coolant, 253F Tranny
After fluid check
@ 68 mph: 226F Oil, 212F Coolant, 194F Tranny

Big change in tranny temperatures and slightly lower coolant temps. And this is consistent on all trips since.

Lessons learned: Double check the work done by someone else on your rig.


Here are the graphs that go with this data. First is the before fluid check run:
1655516642066.png

Next is the After fluid check run:
1655516696761.png
 
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Daniel Ortiz

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@Fritter, am I right that your experimenting suggests that your transmission was overheating due to an over-filled transmission? Let us know if you see it overheating under any other circumstances. To date, I've only been driving mine around in the city, and it gets up to 188 F, but that's about it. Pretty boring. I can't wait till I have some free time to fiddle around with mine.
 

Joe _S2013

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Dan, I did the same thing yesterday, OEM part from MOEPARTSINC(transmission Heater Assembly 68463479AA)was only $139.00. Did your unit come with the plastic heater tubes, or steel and O-rings? -The tubes that go between the transmission and the assembly (under the bigger plastic cover in your pic) . My old one had the steel tubes (68227208AA, 68227207AA), but the new one had the plastic tubes( 68227208AB) , I was going to swap them out but the plastic tubes did not come out very easy, and I did not want to yank too hard and break something. I have been online to try and order the O-rings (68227207AA), but all the sites say the o-ring is discontinued and only a few have the steel tubes most reference the plastic tube part number ( 68227208AB) . I ordered the two replacement part for the tube and O-ring (one part number 68227208AB) and got two plastic tubes. It does not appear to need an O-ring. The fit with new Heater assembly and plastic Tubes seemed as good as the one that came out with the steel tubes and O-rings. I am wondering what you got and what you did?

Also if you had any trouble getting the fill plug out, what you did. Mine wont budge and I started stripping it trying to get it out.
Thanks
 

Fritter

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Dan, you are correct. In my case based on the evidence to date, a significant causal factor in the overheating is the excess transmission fluid. The only changes to the vehicle between the two graphs is mileage, 2 engine oil changes and checking the transmission fluid fill level (with the subsequent removal of 28 fl oz.). How it got that much excess fluid is unknown but I've envisioned a scenario during the initial installation of a replacement tranny back in 2018 due to infant mortality as the potential culprit. If the excess fluid started frothing then the heat rejection capacity of the system via the transmission oil cooler is drastically reduced. And the capability of transporting sufficient tranny fluid (i.e. heat) to the cooler is reduced. The cooling system is designed to work with a homogeneous fluid in a liquid state - not an air & oil mixture. That's the working theory.

I need to take a longer drive at steady highway speeds to ensure it is a true reduction in temperatures, not just rate of change difference. There are some increases in temperatures that did not level off before I had to reduce speed due to traffic. I want to get the vehicle up to a steady speed and hold until the fluid temperatures are stable for 10's of minutes.

On another front - I've looked at the impact of disabling the AGS (by pulling the fuse). There is ~10F drop in the 3 fluid temperatures (oil, coolant, transmission) in the examples to date and the short term variation in temperatures is less. This was during a 1 hour drive (multiple occasions). The temperatures appeared to be stabilized in the case of the AGS disabled but the AGS On case had increasing temperatures before needing to slow down due to traffic. Again, I'm going to need a longer drive to confirm.
 

Joe _S2013

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@Fritter Great information. How did the fluid look when you drained the excess? Also, not sure I fully understand the AGS disablement decreasing temps. My understanding is they start in the shut position and open at approx 200 degrees. So by disabling them (removing the fuse) wouldn't that leave them closed at higher temps and thus reducing the cooling effect and increast the temps? I am in the process of completing the Heater assembly replacement like Dan, due to my temps of 230-250 on the freeway -long and short trips. I would be interested in what you find on how they got 28oz extra fluid in the transmission without doing something drastic, parkin on a hill and angle away from the fill plug.
 

crazykid1994

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I just drove 1.5hr trip today both ways. Approximately 60 miles each way. 50 miles on the interstate at 80 mph. Sustained temps on the ride out at 93° outside were 197° coolant temp, 140° trans temp, 210° oil temp, and 52 psi oil pressure. Rpm is ~2100 at 80 mph. Sustained temps on the ride back at 88° outside was 195° coolant temp, 138° trans temp, 206° oil temp. Trans heater deleted, ags fully removed, relocated filter. About 14-15mpg at 80 mph. Goes up to 17mpg at 75mph and around 19mpg at 70mph.
 

Fritter

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When starting a vehicle the AGS is in the open position. Pulling the fuse prior to starting keeps them in that position (no power to move).

I am interested in the AGS operating points - conditions at which they change position. I have not found any definitive data on it. Here's a summary of other posts - the AGS is designed to help the aerodynamics of the vehicle, especially at higher speeds. AGS would close at some speed (probably close to 50 mph when aero effects become significant enough - from Google search. What I have not found is under what conditions the AGS opens besides speed based (the same 50 mph presumably). I have not seen any indication of it in the data I've collected on my truck but that data is suspect due to the overfill condition. I'll be looking for this in the longer runs but I may not hit the temperature conditions necessary since my temps are starting to look more nominal. I think adding a camera watching the AGS or tapping into the electrical circuit is the best way to get that data.

The transmission fluid removed from the vehicle looked OK given 49k miles / ~5 years but I wouldn't say I have much experience on tranny fluids. I've attached a picture of a few drops of new ATF and ATF removed from my vehicle on an off-white quartz surface. I have not had it tested.

28 fl oz overfill is tough to do - I only have outlandish theories sprinkled with ineptitude or serious lack of attention to detail.
 

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Joe _S2013

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@Fritter great info. I tell people I have a hot truck and they think it is my ego, yet none has disagreed with me, after I show them my temps. -Lol

A lot going on with my 2014 RAM 1500 4x4. Just starting with what I think is the hottest iron in the fire (pun intended), the 250 degree transmission. I just learned about removing the center AGS fins and swapping the 203 degree thermostat with a 185 degree thermostat a couple weeks ago, so now I have more research to do. My goal is to get the transmission temps down to 160 range yet keep my gas mileage (17 MPG is average on freeway at 85 on a 300-400 mile trip w/no load) -I was a navy submariner most of my life (32yrs) worked on cars as a hobby, so not always comfortable with changing engine and transmission components on daily drivers, trying to do OEM parts first, but I have raced a few cars and mod'd a few, mainly Chevy.

I just did the Transmission Heater assembly and filter change yesterday, was able to notch and beat the fill plug off with a sledge and metal punch. -Took longer to do the filter change and fill plug than it did to change the heater assembly, including dropping the exhaust crossover pipe. Had to replace the manifolds about a year ago after fun with 4 (two each side) broken bolts (Hemi tick on both sides), so the crossover was pretty easy. I wish my fluid looked as good as yours. Mine was black and smelled god awful. I replaced it with the unicorn pea OEM stuff, I know some say there are cheaper and just as good, but the temps on this transmission, 230-250 in the summer, just did not make me comfortable, and there did not seem to be anything really wrong with the transmission, so I figure the OEM fluid has to be some type of unicorn *** with magical powers and also why it cost so much. Last nights test run the transmission stayed below 200 which is good for my truck. The next think I am going to do after verifying fluid again (your post has me double and triple checking) is @caulk04 eliminator mod. -I have one just need to install, but want to watch temps first. -I really like your graph and wish I would have thought to do that, just to show how crazy the temps are.

Thanks again and looking forward to see more of your charts.
 

pacofortacos

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AGS will stay closed most of the time - mine will open when
-Coolant exceeds 220 degree or so ( I think 221-223)
-Trans temp exceeds 196 degree
-AC conditions are met - pretty sure it reads the high side pressure
May open over 90+ mph or so I have heard.
There is no 50 mph threshold, I know that for sure.

There may be other parameters that will open or close it, but these are the ones I know of.
 

06 Dodge

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Below is a heat life chart for ATF fluid, I was given this back in 2008...
 

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Joe _S2013

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@pacofortacos, This makes a sense to me after doing some high speed rapid acceleration testing. I just replaced the Transmission Heater Assembly and have an OEM stock thermostat in the Heater Assembly and the stock 203 degree thermostat in the engine. With outside temperature in the 80's, my normal transmission operating temps was (prior to the swap) between 220-230, and 230-250 under heavy acceleration(Northern VA driving).

With the AC on max, I initially had difficulty getting the trans temps w/new unit over 185 degrees, it seemed to get there quick, but wanted to stay. Then with the rapid acceleration I was able to get it into 197 range and I could see the temps gage drop pretty quick back to the 185 range. I then took to the back streets with a lot of stop signs and traffic lights and with more heavy acceleration I was able to get it to 200 degrees, but it then would go fairly quickly (less than 2-3 minutes) back to the 185 range, as I returned to normally acceleration. Without the AC on I could not get the temps over 190 with same driving style and conditions. I believe all of this is coming from the AGS opening, and allowing increased airflow over the radiator (still have mechanical clutch and not electric fans) . The Coolant is showing over 210 and the engine and heater thermostats should be open the whole time.

I have seen many ATF temperature charts, but not sure how they apply to the ZF 8/9 speed Magic Unicorn pea these transmissions have. My truck has 160K has ran hot 200-250 for tens of thousands of miles (way outside the chart parameters above). When I changed the transmission fluid it was as dark as any stout I have drank, smelled God awful, but no chunks in the fluid or pan, and the transmission was running fine (fortunately I found trany temp on the instrument cluster) with a very slight bump when stopping, as other have described, and I believe the bump was due to low fluid. - 4.5 quarts came out and I added 6.5 quarts. I Will go into more detail in a later post that covers all I did and how much it has changed the performance of the transmission.

I have one of @caulk04 eliminator's that I plan to install after more testing to see what my MPG is with the lower transmission temps. I would like to keep my transmission temps below 175, but I have to see the difference in MPG. I saw a 5- 10% increase in MPG in the summer with higher transmission temps. I would like to see the temp chart for the ZF8/9 speed transmission fluid, I am convinced it is magic unicorn P. -Lol. I am sitting her writing this amazed I am not replacing the transmission or at least worried about the one I got.
 

hawsk99gt

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It happened again........Went to Atlanta today, doing some hot highway driving, temps here are around 85 degrees. Was fine on the way down from Northern GA tranny temps were at 145 degrees at 80mph. But on the way back it jumped to 235 while my coolant was at 201 and my oil was a little higher around 203 - 209 at 70 mph. This went on for 30 miles till I hit some crawling road construction. So for a couple of miles my average speed was 5 - 15 mph. Once I got thru that temps dropped to 165 degrees and stayed like that all the way home doing between 70 and 80 mph. I already have CAULK04's thermo by pass installed and it works for the most part. Does anyone think that I may need to get my transmission flushed for debris possibly and have new fluid put in there? Any suggestions, please.
 

Wild one

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It happened again........Went to Atlanta today, doing some hot highway driving, temps here are around 85 degrees. Was fine on the way down from Northern GA tranny temps were at 145 degrees at 80mph. But on the way back it jumped to 235 while my coolant was at 201 and my oil was a little higher around 203 - 209 at 70 mph. This went on for 30 miles till I hit some crawling road construction. So for a couple of miles my average speed was 5 - 15 mph. Once I got thru that temps dropped to 165 degrees and stayed like that all the way home doing between 70 and 80 mph. I already have CAULK04's thermo by pass installed and it works for the most part. Does anyone think that I may need to get my transmission flushed for debris possibly and have new fluid put in there? Any suggestions, please.
Check your A/C condensor over for a bug/dirt build-up. The transmission cooler is in the top half of the A/C condensor,and if it's bunged up with bugs/dirt etc.,your transmission might run warm. I'd pull the grill spray some bug/tar remover specific for condensors/radiators on the condensor and wash the condensor out at your local carwash first,and then go from there. You can also remove the middle slats from the active grill shutters,just leave one top and one bottom fin in place,and the truck won't throw a code ,that's if you still have the active grill shutters in place
 

hawsk99gt

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yeah I still have my active shudders. But wouldn't it be consistently getting hot every time I drive? My other temps are fine. It drove a good 50 miles one way and then parked for an hour in a concrete garage, then the problem began. I'll check the A/C condenser regardless, thanks for the suggestion.
 
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