8HP70 Transmission Heater/Thermal Bypass Valve

[Tach_tech]

The fluid is like water Dan,i'm not sure you'd see much difference in the tranny's operation whether it's at 160F or 185F,lol. I was tempted to bypass the coolant heater when I replaced my tranny,but then decided I wanted to keep some of my high dollar new trannies warrenty,lol.In Canada or the northern States where it gets cold,i think the heater does a good job,but where it doesn't get cold,i'm not so sure the heater is needed.The cars drive year round up here with-out the heater,and it doesn't seem to affect their cold weather operation,so you probably could get away with bypassing the coolant heater up here to,it'll still have the thermostat to regulate the temp after warm-up. My way of thinking is,if the 5.7 and 6.4 cars don't use the coolant heater,the trucks can probably get away with-out it to. The transmission will still get to operating temp as the thermostat is still in place,it'll just take longer to get there. I'm not advocating removing the coolant heater,all i'm saying is I think it can be bypassed,with no real affects to the trucks operation or the transmissions life expectancy.

I was more referring to cold start temperatures. The fluid will be more viscous at those colder temps which will slow/inhibit shifts due to viscosity. That’s where the heater would help. However the differences aren’t night and day by any means.

I’ll agree that would be just fine by removing it as the differences would be very small in operation. At that point you might as well just leave it lol.

On high horsepower and track applications having a slightly cooler temp would be beneficial especially if you run a high stall converter. It will heat up fast. For the vast majority of people though messing with the cooler and thermostat is not worth the hassle.

 

[jjjefferson]

Well here is what you are looking for.....a kit to delete the heater. Yeah I brought back an old thread.... deal with it.

https://revmaxconverters.com/produc...-8hp75-transmission-cooler-thermostat-bypass/

As an owner of 1 bad ZF8 transmission that failed at 50K. It was replaced then 10K later started spiking temps on the highway. I am putting this on immediately!!!! Been looking for one for years..... Sorry Ram ZF8 Heater fanboys.....you could not be more WRONG on this issue.

 

[crazykid1994]

Well here is what you are looking for.....a kit to delete the heater. Yeah I brought back an old thread.... deal with it.

https://revmaxconverters.com/produc...-8hp75-transmission-cooler-thermostat-bypass/

As an owner of 1 bad ZF8 transmission that failed at 50K. It was replaced then 10K later started spiking temps on the highway. I am putting this on immediately!!!! Been looking for one for years..... Sorry Ram ZF8 Heater fanboys.....you could not be more WRONG on this issue.

Message @caulk04 and see if he has any tstat deletes left or do what @Wild one and I did and just pull the heater off and plug the holes in the heater assembly. Look at the temp in my picture for the trans. That’s with the heater assembly deleted. https://www.ramforum.com/threads/8hp70-heater-bypass.172998/

 

[caulk04]

I'm still making my part. Accomplishes the same thing as the revmax kit but does so with a faster and easier install. Maintains 100% stock appearance, too.

 

[Cbisme72]

I know it's long shot, but I have 2017 ram 1500 big horn 5.7...160k miles started get a chatter low speeds...checked level fluid and I have water in w fluid...would the tmv allow for.cross contamination between tranny fluid and radiator? And if so could I bypass it to fix the issue? Thanks much!

 

[Wild one]

I know it's long shot, but I have 2017 ram 1500 big horn 5.7...160k miles started get a chatter low speeds...checked level fluid and I have water in w fluid...would the tmv allow for.cross contamination between tranny fluid and radiator? And if so could I bypass it to fix the issue? Thanks much!

I suppose it could,but if it did crack and allow cross contamination,it's not a very common problem,you'd be the very first one i've heard of having that issue,but anything is possible.There's a few pics in this thread of the bypass and heat exchanger.This thread shows you how to totally delete the heat exchanger,if you think it's your issue,but the last time i checked they weren't that bad in price.You'll need a set of hose clamp pliars similiar to these,to get the hoses off the heat exchanger.

https://www.amazon.com/Astro-Pneumatic-9409A-Clamp-Pliers/dp/B003D3N7YW?th=1

RevMax 8 speed thermostat bypass

Took the wife out for supper tonight,we weren't in any rush and we were on 2 lane back roads,so i had the cruise set at 90 kmh's roughly 56mph,our favorite little eating joint is about 40 miles away,tranny just barely got over 110f in her car.

www.ramforum.com

 

[SpaceRanger1]

2017 Rebel with the 5.7 and the 8HP70 trans.. Changed to the PPE pan at 205K. Got 324100K now with NO issues..

 

[QwikKota]

Great mile count for the Hemi.

 

[Ram Night]

Agreed. No sense in modifying this part if it isn't broken. They engineered this tranny to run like this.

The problem with the stock thermostat is they can fail and overheat the transmission and cause a failure. There are bypass kits that only require the valve and spring to be changed. Plus, they are easy to put back to stock if a warranty problem comes up.

 

[RedSRT4Me]

The problem with the stock thermostat is they can fail and overheat the transmission and cause a failure. There are bypass kits that only require the valve and spring to be changed. Plus, they are easy to put back to stock if a warranty problem comes up.

Who's had failed and overheat? I'm at 190k miles and still trucking. Of course I probably stuck my foot in my mouth saying this.

 

[Wild one]

Who's had failed and overheat? I'm at 190k miles and still trucking. Of course I probably stuck my foot in my mouth saying this.

There's been the odd one fail,you'll find more guys on the facebook pages with a failed one then on here Red.They've also been known to leak coolant internally in the TMU and take out the odd transmission. Alot of times you'll find more of this kind of info on the facebook pages then on here,as there's more guys on the facebook pages then on here.

 

[Ram Night]

Who's had failed and overheat? I'm at 190k miles and still trucking. Of course I probably stuck my foot in my mouth saying this.

Well, it is like anything else mechanical; it can fail at any time. A good example are the cam and lifters.

 

[EdGs]

There's been the odd one fail,you'll find more guys on the facebook pages with a failed one then on here Red.They've also been known to leak coolant internally in the TMU and take out the odd transmission. Alot of times you'll find more of this kind of info on the facebook pages then on here,as there's more guys on the facebook pages then on here.

I'm glad I eliminated the coolant circuit to the heat exchanger on my 8 speed. Jesse's bypass will be installed soon.

 

[Daniel Ortiz]

@RedSRT4Me I was one of the folks that started having the ZF 8HP transmission spiking up to the 230s F. It had ~65,000 miles at the time and I posted about it the week it happened here. The thermostat in the transmission heat exchanger was sticking, leading to the overheating. For most people, the ~180s F transmission operating temperature is merely an annoyance. But for lucky ones like me, it meant I couldn't drive my truck more than 45 minutes before I had to start dropping down to 20 mph periodically to let the transmission cool down. That bypass plug gave me my truck back.

 

[caulk04]

@RedSRT4Me I was one of the folks that started having the ZF 8HP transmission spiking up to the 230s F. It had ~65,000 miles at the time and I posted about it the week it happened here. The thermostat in the transmission heat exchanger was sticking, leading to the overheating. For most people, the ~180s F transmission operating temperature is merely an annoyance. But for us lucky few, it meant I couldn't drive my truck more than 45 minutes before I had to start dropping down to 20 mph periodically to let the transmission cool down. That bypass plug gave me my truck back.

For a few months, I had a prototyped revision to my valve and cap, using the stock thermostat in an orientation that I hoped would 'fail-safe' if the thermostat failed and would also heat up much more slowly than stock. Turns out, my thermostat is also failing. Found out on a 12hr drive to Myrtle Beach early this year. Trans temps climbing up to 225º before I backed off then repeated until the thermostat finally would open and operate normally for a while. I've scrapped that idea and now run the cap and valve like so many others.

FWIW - Well over 600 valves are out there and I believe over 300 caps. EDIT, 719 valves 389 caps and counting.

 

[Daniel Ortiz]

FWIW - Well over 600 valves are out there and I believe over 300 caps.

@caulk04 's progeny.

 

[EdGs]

With my truck having 214k on it, should I think about buying the updated fittings that connect the heat exchanger to the transmission?

AFAIK, the originals have o-rings, and the updated ones are totally different.

 

[RedSRT4Me]

@RedSRT4Me I was one of the folks that started having the ZF 8HP transmission spiking up to the 230s F. It had ~65,000 miles at the time and I posted about it the week it happened here. The thermostat in the transmission heat exchanger was sticking, leading to the overheating. For most people, the ~180s F transmission operating temperature is merely an annoyance. But for lucky ones like me, it meant I couldn't drive my truck more than 45 minutes before I had to start dropping down to 20 mph periodically to let the transmission cool down. That bypass plug gave me my truck back.

Noted. But that's a thermostat failure. Same as if the engine thermostat failed.

Anyone have the min and max that the ZF fluid is run at?

 

[seems fishy]

You guys are OCD

 

[Sherman Bird]

ZF is likely under contractual obligation to no disclose this information. Keep in mind, the 8HP70 is NOT cheap. FCA does not want to replace it. My father had a 5 series with the exact same transmission. Similar temps. Dollars to donuts your transmission will outlast your truck. service it and enjoy it.

My goodness, whatever other hobgoblin will he find to worry over? 180 degree tans temps are stellar, and not measurably that much better than 160.
Transmissions begin to really suffer at oil temps over 240-ish. get up to 275 or more, it will be curtains soon!

All the "new" fluid in the world has additives, just like the older school fluids did. In over 2 decades of being an automatic trans tech for Ford and GM, I can say that high temps are the #1 killer of transmissions. 180 ain't high.

Envision "Whirled Peas"!