8hp70 heater bypass

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Bigskyroadglide

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Adding a different flavor to the thread. Over Thanksgiving holiday drove from Virginia to Tennessee to visit family. Drove down late Wednesday night early Thursday morning, outside temps were in the 25 to 29 degree through the elevated portion of Virginia along interstate 81. My 8 speed, with chaulk's part installed provided for trans temps of 109, as a low for about 3 hours of the 7 hour trip. Avg speed was around 80. After dropping out of the elevated terrain on the western side of Knoxville temps climbed back to 120 and stayed consistent. I have all active grill shutters out except top and bottom rows.

On Saturday before returning to Virginia for work, I reinstalled all of the lower grill shutters, and left the uppers out. Temps this week with the weather in the 20s on the 20 minute trip to work are running 132 to 139. A much more acceptable range.

My trans has always run cooler even before chaulk's part install, however I'm thinking 109 might be a little cool.

Opinions?
 

Daniel Ortiz

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@hawsk99gt I think that would be a good experiment. It looks like the transmission operating temperature is highly dependent on the ability of the trans oil cooler to cool it down once the trans thermal bypass plug is installed.

Also, if you haven't already, I think you should consider doing a transmission fluid level check per the procedure @Wild one has distributed (the infamous green instructions). You wouldn't have to change the majority of the fluid or drop the pan. You'd only need one quart of the stuff from the dealership in case you need to top off, but in all likelihood, you might not even need that, since there's a good chance fluid will actually drain out if you follow the procedure correctly, since it seems these transmissions may be over-filled at times (which is my concern here).

Following the procedure isn't a walk in the park, but it's also not rocket science. Many of us here have perfected it by now an would be happy to walk you through it. You'd need to be able to jack up the rear end quite a bit onto jack stands for the 1-2 shift (turn traction control off, back tires will need to spin). Also, wear gloves (fill plug is tight and near exhaust pipes), and get a way to pump the trans fluid into the fill hole (again, only if none comes out during the level check in the procedure).

I think doing a proper trans fluid level check would give you some peace of mind at the very least. It'd be one less variable you'd have to consider in your quest to diagnose the problem.
 

Different Drummer

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Adding a different flavor to the thread. Over Thanksgiving holiday drove from Virginia to Tennessee to visit family. Drove down late Wednesday night early Thursday morning, outside temps were in the 25 to 29 degree through the elevated portion of Virginia along interstate 81. My 8 speed, with chaulk's part installed provided for trans temps of 109, as a low for about 3 hours of the 7 hour trip. Avg speed was around 80. After dropping out of the elevated terrain on the western side of Knoxville temps climbed back to 120 and stayed consistent. I have all active grill shutters out except top and bottom rows.

On Saturday before returning to Virginia for work, I reinstalled all of the lower grill shutters, and left the uppers out. Temps this week with the weather in the 20s on the 20 minute trip to work are running 132 to 139. A much more acceptable range.

My trans has always run cooler even before chaulk's part install, however I'm thinking 109 might be a little cool.

Opinions?
Consider replacing the upper shutters instead of the lower shutters if you are trying to get your Transmission Temp. increased a bit. I believe that the transmission cools through the upper section of the A/C condenser unit. Don't know if this would allow less air to the Transmission cooler but might be worth a try.
I agree,, Temps at and below 120 would not be to my liking. 140 -170 would be a goal IMO.
 
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Bigskyroadglide

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Consider replacing the upper shutters instead of the lower shutters if you are trying to get your Transmission Temp. increased a bit. I believe that the transmission cools through the upper section of the A/C condenser unit. Don't know if this would allow less air to the Transmission cooler but might be worth a try.
I agree,, Temps at and below 120 would not be to my liking. 140 -170 would be a goal IMO.
Right now having the lowers in is producing 130 to 140 temps on my daily commute.

I'm supercharged and have to account for a liquid to air intercooler which is mounted high, that's why I left the uppers open.
 

Dean2

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You know guys, at least on stock trucks, this is a tremendous amount of screwing around to fix something that so far hasn't been much of a problem. The active shutters and transmission heat helps tons up here in cold weather, and so far, even in hot country with lots of towing there are very few 8 speeds that fail. Seems like a ton of futzing for very little gain.
 

Wild one

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You know guys, at least on stock trucks, this is a tremendous amount of screwing around to fix something that so far hasn't been much of a problem. The active shutters and transmission heat helps tons up here in cold weather, and so far, even in hot country with lots of towing there are very few 8 speeds that fail. Seems like a ton of futzing for very little gain.
If you have the 8 speed behind your 6.4,it doesn't have the coolant heater,and should also run right around 165 to 170 on transmission temp,while the 1500's will run roughly 20 degrees hotter.Must be a reason why they don't heat the fluid on the 2500's and use a colder activated thermostat pellet in their transmission thermostat Dean
 

Dean2

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If you have the 8 speed behind your 6.4,it doesn't have the coolant heater,and should also run right around 165 to 170 on transmission temp,while the 1500's will run roughly 20 degrees hotter.Must be a reason why they don't heat the fluid on the 2500's and use a colder activated thermostat pellet in their transmission thermostat Dean
Yes, 2500 tend to pull more weight. That said, how many 1500s are scrapping out because of 8 speed tranny failures. My point isn't tha temp they run at, it is the amount of screwing around to fix something that isn't causing major problems.
 

Wild one

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Yes, 2500 tend to pull more weight. That said, how many 1500s are scrapping out because of 8 speed tranny failures. My point isn't tha temp they run at, it is the amount of screwing around to fix something that isn't causing major problems.
Some guys are having issues with heat though.The majority of guys messing around with the transmission thermostat are doing it because they're having heat issues.Even when the thermostat is fully open,it still doesn't allow for full cooler flow,as it's still a restriction.If they ran the same 165 transmission thermostat as the 2500's get,nobody would be messing with the thermostat
 

MRFREEZE57

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I use to get as high as 185 deg on a warm day not towing anything, with Calk's bypass the highest has been about 160 deg. Now during the colder temp it takes a while to warm up and will go to around 130 deg and rise a bit more if in slow traffic.
Don't know why Chrysler does not use a 150 deg T stat instead of the one they come with.
 

hawsk99gt

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Yep, already did the transmission fluid check. I did try to do it myself and it was just a disaster trying to get it leveled. So I said the heck with it and had the dealership check the level. They had it for a couple of days and they said the level was good and the condition of the fluid was fine. But thanks for the input.
 

ARONUSA

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2017 ram 1500 sport, maxlife atf and dorman pan,

Regular highway transmission temps were 195-201

tried 180 thermostat and removing shutters, didnt help at all.

just put in chaulks bypass max temp running hard is 167. What a difference, thank you so much, theres no way these transmissions are suppose to be running over 200 degrees all the time not even towing. I feel much better about it now.
 

Fritter

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Reporting in after gathering more data on truck operation.

Installed a 190 t-stat (Stant 48799 with Motorad stamping) and removed the AGS (middle shutters only).

Average temperatures:
Engine coolant 194 +/- 3 deg F
Transmission fluid 181 +/- 4 deg F
Engine oil 206 +/- 4 deg F

Engine oil pressure 55 psi

Went cross country along Interstate 40. During long climb heading east bound into Flagstaff (speed between 75 and 80 mph) the engine coolant and engine oil temperatures climbed to 197 F and 212 F respectively. Transmission fluid temperature increased to 194 F then spiked to 210 F in less than 10 minutes before I could pull into a rest stop. Decreasing speed to the low 60's did not help. Allowed fluid to cool to ~190 F then hit the road. The fluid temperatures decreased to the averages after about 15 minutes at speed. About an hour later the same thing happened with the exception that the fluid spiked to 220 F before I could stop. After stopping in Flagstaff for about an hour the temperature spike occurred again on another climb heading toward Albuquerque; this time the temperature increased to 230 F before I was able to get off the highway. In all three cases the temperatures did not appear to be stabilizing before I stopped.

Circumstantial indications that at 77 mph and below the cooling system was stable and could handle some of the grades. Above that the transmission fluid temperature could/would rise and be prone to the spike. This is gut feel.

For the return trip I installed caulk04's bypass (aka t-stat eliminator). Engine coolant and oil temperatures were the same as the outbound trip but now the transmission average temperature was 127 +/- 6 deg F. No spikes the whole 2,000 mile drive westbound on I40 regardless of the climbs at 75-80 mph (passing trucks). The OAT was in the 20's F in the morning topping out at upper 50's F during the day. Only downside was how long it takes for the transmission fluid to get to temperature in these conditions. The caulk04 eliminator works as discussed in this forum - big THANKS to caulk04.

Now back home, when operating in mild conditions (50's and 60's F), the fluid gets to the 130's (133 to 137 F) within 12 miles at 40-45 mph in suburban driving.

I’m going to monitor the transmission temperatures over the next few months to see if an IR 145 F inline thermostat is needed (for my conditions) to get up to temperature faster with stable transmission temperatures in the 150-170 F range. Also, a fluid change is in the immediate future (after 57k miles and numerous spikes as high as 262 F before the t-stat change and AGS removal).

The remaining unknown is the torque converter operation. Which tuner/tool would be best to determine TC operation and adjust set points if necessary?
- This correlates to the thread "2014 Ram 1500 8 speed transmission “spike overheat” - discussion".
 

Mr onetwo

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just food for thought...BMW does the same thing in the 335i and others. I have purchased one of Caulk's pieces and will document the findings.
 

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HEMIMANN

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Reporting in after gathering more data on truck operation.

Installed a 190 t-stat (Stant 48799 with Motorad stamping) and removed the AGS (middle shutters only).

Average temperatures:
Engine coolant 194 +/- 3 deg F
Transmission fluid 181 +/- 4 deg F
Engine oil 206 +/- 4 deg F

Engine oil pressure 55 psi

Went cross country along Interstate 40. During long climb heading east bound into Flagstaff (speed between 75 and 80 mph) the engine coolant and engine oil temperatures climbed to 197 F and 212 F respectively. Transmission fluid temperature increased to 194 F then spiked to 210 F in less than 10 minutes before I could pull into a rest stop. Decreasing speed to the low 60's did not help. Allowed fluid to cool to ~190 F then hit the road. The fluid temperatures decreased to the averages after about 15 minutes at speed. About an hour later the same thing happened with the exception that the fluid spiked to 220 F before I could stop. After stopping in Flagstaff for about an hour the temperature spike occurred again on another climb heading toward Albuquerque; this time the temperature increased to 230 F before I was able to get off the highway. In all three cases the temperatures did not appear to be stabilizing before I stopped.

Circumstantial indications that at 77 mph and below the cooling system was stable and could handle some of the grades. Above that the transmission fluid temperature could/would rise and be prone to the spike. This is gut feel.

For the return trip I installed caulk04's bypass (aka t-stat eliminator). Engine coolant and oil temperatures were the same as the outbound trip but now the transmission average temperature was 127 +/- 6 deg F. No spikes the whole 2,000 mile drive westbound on I40 regardless of the climbs at 75-80 mph (passing trucks). The OAT was in the 20's F in the morning topping out at upper 50's F during the day. Only downside was how long it takes for the transmission fluid to get to temperature in these conditions. The caulk04 eliminator works as discussed in this forum - big THANKS to caulk04.

Now back home, when operating in mild conditions (50's and 60's F), the fluid gets to the 130's (133 to 137 F) within 12 miles at 40-45 mph in suburban driving.

I’m going to monitor the transmission temperatures over the next few months to see if an IR 145 F inline thermostat is needed (for my conditions) to get up to temperature faster with stable transmission temperatures in the 150-170 F range. Also, a fluid change is in the immediate future (after 57k miles and numerous spikes as high as 262 F before the t-stat change and AGS removal).

The remaining unknown is the torque converter operation. Which tuner/tool would be best to determine TC operation and adjust set points if necessary?
- This correlates to the thread "2014 Ram 1500 8 speed transmission “spike overheat” - discussion".

@caulk04 does excellent work.

I've always said on here, do we really care how cool transmission oil gets? Who cares if it reduces fuel economy 0.001%? The only thing a transmission oil thermostat would be good for is arctic conditions so the trans doesn't shift so stiff. But that requires a ROBUST design with a proper sized thermostat housing - not the pencil hole and cheap little thermostat MOPAR uses.

Don't worry about it. You're fixed - your tranny will no longer overheat and varnish burned oil all over it.
 

crazykid1994

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The zf8 transmission does shift differently under 120°F and since installing my inline thermostat to bring temps up some I noticed my whole truck feels happier. Trans is shifting smoother and quicker below the 186° temp. Below 120° the trans shifts very blocky in my truck. I also noticed the mpg seems a pinch higher since adding the inline thermostat.
just food for thought...BMW does the same thing in the 335i and others. I have purchased one of Caulk's pieces and will document the findings.
If I remember correctly bmw runs them in the 180°-190° range same as ram.

@caulk04 does excellent work.

I've always said on here, do we really care how cool transmission oil gets? Who cares if it reduces fuel economy 0.001%? The only thing a transmission oil thermostat would be good for is arctic conditions so the trans doesn't shift so stiff. But that requires a ROBUST design with a proper sized thermostat housing - not the pencil hole and cheap little thermostat MOPAR uses.

Don't worry about it. You're fixed - your tranny will no longer overheat and varnish burned oil all over it.
It’s not so much how cold you can get it. They have an optimal operating temp. The bmw forum actually has a write up on transmission function and how it actually operates smoother hotter and they see better transmission life with warmer temps. The oil expands as it heats up and it gets thinner. Too thick and it can’t fully lubricate and to thin it gets squished out. Someone needs to take some zf8 fluid and heat it in a tube to see temp correlation to expansion and viscosity
 

HEMIMANN

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The zf8 transmission does shift differently under 120°F and since installing my inline thermostat to bring temps up some I noticed my whole truck feels happier. Trans is shifting smoother and quicker below the 186° temp. Below 120° the trans shifts very blocky in my truck. I also noticed the mpg seems a pinch higher since adding the inline thermostat.

If I remember correctly bmw runs them in the 180°-190° range same as ram.


It’s not so much how cold you can get it. They have an optimal operating temp. The bmw forum actually has a write up on transmission function and how it actually operates smoother hotter and they see better transmission life with warmer temps. The oil expands as it heats up and it gets thinner. Too thick and it can’t fully lubricate and to thin it gets squished out. Someone needs to take some zf8 fluid and heat it in a tube to see temp correlation to expansion and viscosity
Of course there's an optimal viscosity range. Before the advent of thermostats and heaters we just lived with it at cold ambient, was my point.
Don't care how many planetaries there are, it's the same issue. Trannys still lasted a long time this way. They don't if overheated.
So MOPARs design was detrimental and shortened transmission life.

I certainly agree if a reliable heater and thermostat is employed the transmission will last longer from less cold ambient wear.
As for my own 66RFE, I don't worry about it. It was overheating with the tiny MOPAR thermostat.
 

ramffml

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Interesting thread. One little data point from a 5th gen while towing a trailer for 3.5 to 4 hours straight, I don't think I've seen temps > 188F.

But I've done very little city or stop/go towing too, still I haven't been concerned about tranny temps. Oil temps have gotten hotter than I'm comfortable with though.

Pic below is pretty accurate for what I've seen for freeway towing. This was taken while running M1 0w-40. Everything was stock as far as cooling goes, I have now removed my AGS but that was after this trip.

LYsaDLd.png
 

HEMIMANN

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85C is too hot.
MOPAR says it's "normal".

It wasn't "normal" before they started screwing around adding thermostats. I wrote up a page of nominal oil oxidation life vs temperature. Running elevated temps means frequent oil changes, which are a beetch to do on a ZF.
 

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