RevMax 8 speed thermostat bypass

[Wild one]

Even in the cold my shortest trip would still get the trans to 140-ish. Definitely higher than 120.

And yes, trans fluid expands so I would be concerned the expansion thats taken into account during engineering and design might not quite be there at a fluid temp of 120. And keep in mind during a day like today where its 30F outside, I probably wouldnt even hit 120.

A cars 8sp won't either,and i know of a few 6.4's that get the crap beat out of them with tranny temps under 100F. There's probably a few 6.4 HD's that abuse the 8 speed ,long before it's at 100F too.Any company 3/4 ton,with a younger driver,probably gets abused pretty hard when cold,and by cold i mean the tranny is still at -20C,but the driver has his boot stuck through the floor,lol. I've never actually heard of an 8 speed or any tranny for that matter,scattering parts from being to cold,but they'll definitely scatter parts from being to hot.

 

[crazykid1994]

Even in the cold my shortest trip would still get the trans to 140-ish. Definitely higher than 120.

And yes, trans fluid expands so I would be concerned the expansion thats taken into account during engineering and design might not quite be there at a fluid temp of 120. And keep in mind during a day like today where its 30F outside, I probably wouldnt even hit 120.

My engine temps take 10 minutes to even get passed 160 when it’s cold out so my trans temp would have to take even longer. I did think about the thermal expansions well, but the engineers also would have to account for that on cold days where people are leaving the house and temps are under 50° F. Trans full spec says to check fluid between 86° and 122° In your idea under 86° the temp fluid would be to low to properly function. My fluid was checked at 80° As it says to fill when under 86° and then warm to between 86-122° and check level.

 

[Wild one]

My engine temps take 10 minutes to even get passed 160 when it’s cold out so my trans temp would have to take even longer. I did think about the thermal expansions well, but the engineers also would have to account for that on cold days where people are leaving the house and temps are under 50° F. Trans full spec says to check fluid between 86° and 122° In your idea under 86° the temp fluid would be to low to properly function. My fluid was checked at 80° As it says to fill when under 86° and then warm to between 86-122° and check level.

Being as how ZF is Germany based,i'd lay odds the transmission has been engineered to handle -20 temps while being abused and still live. They'll have planned around the average driver who doesn't pay any attention to engine /oil or tranny temps before they start beating on the vehicle. We're a select few,who do pay attention to temps,the majority of owners don't,you could even do a poll on here to find out how many guys actually have the evicc on the temps and not the speedo,and it's probably more on the speedo then we think.My truck is always on the temps,but i'm always amazed at the amount of guys who have the evicc on the speedo

 

[Different Drummer]

Given that a lot of people have short drives and the trans takes a bit to warm up I doubt many people get much higher. Not to include that older vehicles did not have a trans warmer and maintained low trans oil temps as well. I know the zf is a completely different setup. However, The cars do not include a oil warmer and would maintain low temps as well. Do I think an aftermarket bypass thermostat, like the HD trucks have, would be great in place of the stock thermostat housing unit with heater? Yes I do. That would be the best option and I would jump right on that boat if someone offered one. 160° would be great in my opinion. I do not think an aftermarket replacement thermostat to replace the stock thermostat will really do much given the thermostat does not fully block the heater from flowing and will continue to heat fluid beyond 160°. I do have to argue that a lot of people are nervous about the low temps. I have never experienced shifting issues in my truck at low temps when the truck is first started. And actually on that 12 hour drive my truck seemed to be more responsive on shifting. It shifted faster and when passing on the highway would drop right into gear and go. At 185° or 190° I always felt like it hesitated briefly when fully warmed up before down shifting.
Edit: speaking of which. Now that I’m thinking about it I really do wish someone would make a bypass style replacement for our trucks to replace the whole assembly. I’m seeing most dodge cars run 165-175° unless running a cooler bypass. BMW runs 195°-205° trans temps on their zf trans. The only thing I’m seeing with research on the fluid is expansion and viscosity change but the zf viscosity is designed to not change drastically from cold to OT. However it does expand quite a bit.

I did not mention it earlier as you folks were really getting into it.
Why couldn't someone just purchase the transmission fluid thermostatic block that is used on the HD trucks? Would just need a mounting place and some plumbing to place it in line. Might be able to utilize some aircraft AN hardware and flexible braided hydraulic lines if and where any bends are required.

 

[crazykid1994]

I did not mention it earlier as you folks were really getting into it.
Why couldn't someone just purchase the transmission fluid thermostatic block that is used on the HD trucks? Would just need a mounting place and some plumbing to place it in line. Might be able to utilize some aircraft AN hardware and flexible braided hydraulic lines if and where any bends are required.

I’d rather something straight drop in so it looks factory and uses factory components instead of cutting and flaring lines. There are other bypass valve options out there that I’ve looked at but just do not feel like having to mock up and modify perfectly good factory lines and if it fails it would be more costly to fix.

 

[caulk04]

Ok, I've received the stock thermostat from crazykid1994 and had a look at it. Here's a couple pics showing how fluid flows through the housing given the information I have. First is when the fluid is hot, how it flows toward the cooler. Next is how it flows cold toward the heater.

Last is the thermostat assembly all broken down, I now have a plan for what I'll make. The plan now is to replace only the thermostat portion itself (I'm pointing at it) and reuse all of the other pieces.

 

[Wild one]

I did not mention it earlier as you folks were really getting into it.
Why couldn't someone just purchase the transmission fluid thermostatic block that is used on the HD trucks? Would just need a mounting place and some plumbing to place it in line. Might be able to utilize some aircraft AN hardware and flexible braided hydraulic lines if and where any bends are required.

Don't quote me on this,but i think the factory lines use a metric sized fitting ,thats not easy to find. I have considered seeing if a guy could find a wrecked 2500/3500 and get the thermostat block and a portion of the factory lines off it,then frankenstein the lines together with the stock lines on our trucks.

 

[Wild one]

I even question how much the fluid expands after 122F,to me i think the fluids expansion rate isn't all that much ,i'd lean more towards the clutches/steels etc. expansion rates being the cause to the fluid levels change.
I wished i'd kept the old fluid from my last change,and chucked it in a measured beaker and checked the level with the fluid cold,then rechecked the level after warming the fluid up to 122F and then to 180F,just to see how much differance there is in the volumne change from cold to hot

 

[Different Drummer]

I’d rather something straight drop in so it looks factory and uses factory components instead of cutting and flaring lines. There are other bypass valve options out there that I’ve looked at but just do not feel like having to mock up and modify perfectly good factory lines and if it fails it would be more costly to fix.

I hear you on keeping it looking factory. Seems like you have passed that point though. One thing I wonder about is how the transmission fluid enters and exits the transmission on the HD truck. In the 1500 you must use the portion that you plugged as it uses the two tubes with the O-rings as the entry and exit for fluid into the transmission. With the HD trucks not having the heater assembly perhaps they have a different arrangement. Im just thinking out loud.

 

[Wild one]

I hear you on keeping it looking factory. Seems like you have passed that point though. One thing I wonder about is how the transmission fluid enters and exits the transmission on the HD truck. In the 1500 you must use the portion that you plugged as it uses the two tubes with the O-rings as the entry and exit for fluid into the transmission. With the HD trucks not having the heater assembly perhaps they have a different arrangement. Im just thinking out loud.

I can't coment on the HD's version,as i haven't crawled under one yet and looked,but i'm gonna guess it's similiar to the cars set-up,which uses threaded fittings to attach the cooler lines to the tranny case.Our trucks use the oddball push in transfer tubes,while the cars transmission case is actually tapped for threaded fittings.

 

[crazykid1994]

I hear you on keeping it looking factory. Seems like you have passed that point though. One thing I wonder about is how the transmission fluid enters and exits the transmission on the HD truck. In the 1500 you must use the portion that you plugged as it uses the two tubes with the O-rings as the entry and exit for fluid into the transmission. With the HD trucks not having the heater assembly perhaps they have a different arrangement. Im just thinking out loud.

I’m still using all straight factory parts though. The housing with the o ring tubes that holds the thermostat and routes the fluid flow is still fully intact. Just the heater assembly has been removed and plugged off. In theory someone could build a 160 bypass style thermostat housing there. Essentially by removing the coolant but without plugging the hoses that’s what you get but your thermostat is still a 180 so it doesn’t go to the radiator till 180 which essentially pointless since it’s still 180

 

[crazykid1994]

I can't coment on the HD's version,as i haven't crawled under one yet and looked,but i'm gonna guess it's similiar to the cars set-up,which uses threaded fittings to attach the cooler lines to the tranny case.Our trucks use the oddball push in transfer tubes,while the cars transmission case is actually tapped for threaded fittings.

Probably less likely to leak like that too.

 

[Different Drummer]

Wild one, When yours was apart did you happen to notice what the inside diameter of the coolant hose exiting the 3 way diverter valve is? Or, care to take a guess?

 

[Wild one]

Wild one, When yours was apart did you happen to notice what the inside diameter of the coolant hose exiting the 3 way diverter valve is? Or, care to take a guess?

The heater /coolant hoses are 3/4" DD

 

[Different Drummer]

The heater /coolant hoses are 3/4" DD

Thanks

 

[crazykid1994]

Had a great conversation with mike. There are a few guys running these trans upwards of 800hp. They have pulled the heaters off and all had the same results. Said it’s holding higher line pressure better. Firmer gear shifts and better clamping force on the clutch packs. Said in the higher HP range they are getting less slip in the trans. He’s currently waiting on hellraiser to get him a hp75 internals upgrade for his transmission to hold 1100 hp. He dailies his truck and said it feels a lot better driving around than it did prior

 

[Wild one]

Had a great conversation with mike. There are a few guys running these trans upwards of 800hp. They have pulled the heaters off and all had the same results. Said it’s holding higher line pressure better. Firmer gear shifts and better clamping force on the clutch packs. Said in the higher HP range they are getting less slip in the trans. He’s currently waiting on hellraiser to get him a hp75 internals upgrade for his transmission to hold 1100 hp. He dailies his truck and said it feels a lot better driving around than it did prior

My facebook messages have been active lately with guys wanting to know how we've plugged the bypass holes and not spent much money to do it,lol. I'd guess in the last week,there's probably been a 1/2 dozen or more trucks that have done the 5/16's set screw plug trick now.

 

[caulk04]

So... Doing more reading and thinking, I came across info that conflicts with what I was told here about flow direction between the trans and thermal unit. Seems it flows out the lower port on the trans which would pressurize the deepest port of the thermostat housing first. This reinforces my idea in that there is a bypass for the fluid should the heater and cooler become blocked. The plug I've made retains this function.

Note on this model which of the lines to the cooler is red (hot from trans) and where that corresponds on the assembly.

At any rate it's more food for thought, I have my part made and just need to make time to fit it and test it some. My daily commute ends with trans temps between 150-160 starting at 50-55 in the morning and whatever ambient is in the evening (20-30 lately) so it'll be interesting to see the effect of full cooler flow on an otherwise stock, un molested truck.

 

[chrisbh17]

So... Doing more reading and thinking, I came across info that conflicts with what I was told here about flow direction between the trans and thermal unit. Seems it flows out the lower port on the trans which would pressurize the deepest port of the thermostat housing first. This reinforces my idea in that there is a bypass for the fluid should the heater and cooler become blocked. The plug I've made retains this function.

Note on this model which of the lines to the cooler is red (hot from trans) and where that corresponds on the assembly. View attachment 236439

At any rate it's more food for thought, I have my part made and just need to make time to fit it and test it some. My daily commute ends with trans temps between 150-160 starting at 50-55 in the morning and whatever ambient is in the evening (20-30 lately) so it'll be interesting to see the effect of full cooler flow on an otherwise stock, un molested truck.

Keep us posted! I might be interested in your updated part since it seems like it would retain factory "look".

 

[Musky Mike]

So... Doing more reading and thinking, I came across info that conflicts with what I was told here about flow direction between the trans and thermal unit. Seems it flows out the lower port on the trans which would pressurize the deepest port of the thermostat housing first. This reinforces my idea in that there is a bypass for the fluid should the heater and cooler become blocked. The plug I've made retains this function.

Note on this model which of the lines to the cooler is red (hot from trans) and where that corresponds on the assembly. View attachment 236439

At any rate it's more food for thought, I have my part made and just need to make time to fit it and test it some. My daily commute ends with trans temps between 150-160 starting at 50-55 in the morning and whatever ambient is in the evening (20-30 lately) so it'll be interesting to see the effect of full cooler flow on an otherwise stock, un molested truck.

What is your part?