Revmax cooler for the 8 speed

[Hookedup87]

Quick question. Was reading a pretty lengthy thread on this subject and couldn’t find a definitive answer on which way to go. What have most of you that have done this mod gone with? Option 1,2 or 3. And the reason the coolant temp and oil temps increase with this mod simply because the coolant is pulling more heat from the trans so it has to go somewhere?

 

[18GSMRam]

I went with option 3, blocking plate and removing the thermostatic valve.

 

[Huskerland]

If you only remove the thermostat, the trans won't push any fluid through the cooler, only the heater. Bad.

If you only install the block off plate, the trans will still make it's way to ~175° before the thermostat opens. Operating temp won't be lowered, it'll just take longer to get there.

Installing both will do exactly the same thing as my bypass valve, but it costs you more money and is more work to install. The brass plug they sell you doesn't solve anything.

I'll sell you my part for $30.

Coolant temps rise slightly when you do this to a stock truck because the PCM keeps the shutters closed trying to raise trans temps.

 

[Huskerland]

What is your $30 part and why does it work?
Thanks

 

[caulk04]

IMG_20210203_195844874

• caulk04
• Mar 11, 2021

That's what it is.

What it does is replicate the factory thermostat function in the full hot/open condition. Everything else in the system works as normal, but the fluid does not flow through the heater and instead only flows through the cooler. At all times.

 

[olscout]

In case anyone is wondering, Caulk 04's valve also fits the 8hp45 behind the Pentastar. Did mine today, temps are much lower. I'll try to post a pic, this was after about 35 minutes of driving back roads, including some 70 mph dashes. I have deleted all but the top and bottom shutters, so everything runs cooler.

 

[15 Handicap]

In case anyone is wondering, Caulk 04's valve also fits the 8hp45 behind the Pentastar. Did mine today, temps are much lower. I'll try to post a pic, this was after about 35 minutes of driving back roads, including some 70 mph dashes. I have deleted all but the top and bottom shutters, so everything runs cooler.View attachment 241991

What about heat when it's cold?

 

[Wild one]

What about heat when it's cold?

The cars and the heavy duty 2500's and 3500's don't heat the fluid,only the 1500's heat the fluid. They seem to do perfectly fine. This was my wifes stock 2019 6.4 Challenger from a week ago after a 40 mile trip babying the **** out of it,to see how low i could keep the tranny fluid temp.****** pic as i don't normally run a camera when i'm driving,but the tranny just barely got over 110F ,that was a day when the outdoor temp was about 39F,and by babying it,i mean i lost speed going up the hills and gained a bit of speed going down the hills,and the highest speed i hit was 55 mph going downhill.I was on a mission to see how low i could keep the transmissions temperature on a 40 mile trip.Appears like the trannies will run perfectly fine at temps under 120F. FYI the guys with the 6.4's in the heavy duties are only seeing temps of 165/168'ish while towing 10,000+lbs,and are seeing right around 160/165'ish running down the road empty.The transmission was engineered in Germany and i'm guessing the engineers planned for it to be beat on when cold,as Germany's not the warmest country in the winter,it's also not that cold ,but it's far colder then Florida is,lol.I've never seen an automatic transmission blow up or scatter it's guts for being to cold,but i've sure seen lots blow up from being to hot,take that as you will,lol. You're the same age as me,whens the last time you seen an automatic transmission scatter parts from being to cold,and that's with ATF which is far thicker then the water they call transmission fluid in the 8 speeds

 

[HEMIMANN]

I know this is an 8sp thread, but I ordered the RevMax thru-block for my 6sp 66RFE. I'm pretty sure that legacy tranny only has the stat routed for the cooler, much like engine coolant and radiator?

 

[caulk04]

The RFE trans uses the t-stat only to control flow through the cooler, or straight back to the trans. I don't know what temp that t-stat opens, but it seems they're rather prone to failure which leaves you with no trans cooler.

The ZF either flows through the heater, or the cooler. Eventually temps level out and it blends between the two. That temp seems to be between 175 and 195. Far too high, IMO. Unnecessary.

 

[HEMIMANN]

The RFE trans uses the t-stat only to control flow through the cooler, or straight back to the trans. I don't know what temp that t-stat opens, but it seems they're rather prone to failure which leaves you with no trans cooler.

The ZF either flows through the heater, or the cooler. Eventually temps level out and it blends between the two. That temp seems to be between 175 and 195. Far too high, IMO. Unnecessary.

Thanks for confirming. I bought a RevMax thermostat replacement through-block. Glad that's all I have to do for 66RFE trans.

Germans over-engineer everything. A great-performing transmission didn't need to screw it up with crazy thermal control systems and no fill and drain - not to mention a plastic oil pan.

 

[Sandevino]

2020 2500 w/ 6.4 at operating temp running empty. The transmission temps will gradually creep up to 150/160’s and stay there no matter what it’s doing.

 

[joesstripclub]

That's what it is.

What it does is replicate the factory thermostat function in the full hot/open condition. Everything else in the system works as normal, but the fluid does not flow through the heater and instead only flows through the cooler. At all times.

Without going back through the giant thread, can you just install your thermostat replacement or does that end up with the same issue as the Revmax kit? I assumed you guys blocked off the heater ports as well to keep fluid from only going through the heater.

 

[joesstripclub]

To reply to OP, I did the revmax kit with option three. I only drive about 10 miles to work, but even on a cold snowy Colorado morning I am still hitting 100 degrees on the trans temp. We hit almost 70 this weekend and was around 140 driving around. I think with the revmax kit or just plugging the heater ports you will get a small amount of heat transfer, but nothing near the stock setup.

 

[caulk04]

My part will accomplish the same as doing the Revmax kit in full (removing thermostat and installing block off plate). My method is just simpler to install and cheaper. Mine is also totally invisible from the outside and even inside you'd likely not know anything was not stock unless you were familiar with the system or had another to compare with.

Rerouting the coolant away from the heat exchanger will drastically slow the heating of the trans, but the thermostat will still, ultimately, determine the operating temp as it won't flow any fluid through the cooler until it opens at 175 or whatever.

EDIT -

Rereading, I don't think I clearly answered your question.

My part stops all flow of trans fluid through the heater. So does the Revmax kit, if installed fully (option 3).

 

[HEMIMANN]

Look at this **** from my RFE66 today. Note the ambient outdoor temp, then the trans temp. Unloaded.
What a crock.

Waiting for my RevMax block. When I worked at Mobil as Lube Service Engineer, the oil oxidation test curves closely approximated the equation of oxidation doubling for every 20 deg increase in bulk oil temp.
These trans are running 165+, should be 140. Trans oil life is cut more than half.

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