66RFE Lifespan

[FlatbedHemi]

My wife’s uncle just bouth a 3rg gen cummins and not a month later the transmission pooped out on him. Truck had around 150k. They took it to a reputable repair shop and they said nothing good about that trans. They also said “They ALL”, meaning any Dodge transmission, go out around 150-180k, “if you work them”.

My truck has the 6.4 and the 66rfe, running 35” tires, steel utility/hay spear flatbed, with about 125k on the clock, that is my work horse on the weekends, and I started getting concerned. So, I got online and started doing research. I have seen more than a few posts about the 66rfe and its problems. However, I also got to wonder if having the truck regeared would help save the transmission. My truck has been running 4.88s since 75k miles, which is about when I started really working it. So, while I’m sitting here wondering how much life my transmission has left in it, I saw where someone posted and pointed out that you only see the problems when you search online, so you never know how many are out there running problem free.

So that got me to thinking, how many 66rfes are there running high miles problem free?

How many people have had problems even though they modified their drivetrain?

How many miles was on it when the trans died?

 

[Hemi395]

I think the RFEs in general get a bad reputation mainly from people tuning their trucks and smoking the transmission. Then you couple that with the ridiculously long fluid change intervals (60k for severe service 120k for "normal" service) and the inline tstat that keeps the trans fluid above 170⁰ you have the makings of a trans that will only last 170k give or take.

@U&A has the same engine trans as you and can provide some actual temps with the tstat bypassed and much more frequent fluid/filter changes.

My truck has the 65RFE and it has been a fantastic trans. My truck has towed our camper all over the country with 0 issues. Currently has 94k on it but I've changed the fluid/filters 4 times with yearly drain/fills in between. RFEs like cooler temps and ultra clean fluid.

 

[U&A]

Do the bypass delete. Best bang for you buck trans mod that HELPS life span. Fluid temperature is always directly related to transmission lifespan. If it runs hot it wont last as long. Fluid deposits happen the hotter it is too.

Hot summer days (80-90F)I see 120-140 not towing whereas before I did the bypass delete minimum temp at full operating temperature was 172 or higher. Even saw 180’s NOT TOWING. The ONLY reason they designed them to run this hot is to get that fraction of a percentage better mile per gallon so they can get their EPA points. In the end, Chrysler (and all the others) is literally forced to do the stuff. I’m sure if they had a choice they would be making them without it. Part of the reason all the new transmissions use water thin fluid. My wifes ranger uses “ULV” or Ultra Low Viscosity” fluid. Stuff is insanely thin.

If I tow 5,000-6,000 lbs in the same 80-90 temps my trans temps actually still never break 140. The difference is amazing.

keep you trans fluid changes old school. Meaning no more than 30,000 miles for fluid.

I shoot for 20,000 mile intervals. I do fluid every 20,000 and fliters every other time. if you get yourself a trans pan with a drain plug and you wont have to actually drop the pan every time. Makes it a cake walk. I got an unpainted PML pan. Not all purty. Its a function over form kinda pan. Very stout. https://yourcovers.com/

Biggest things that the RFE does not like is hard down shifts, especially into fourth from sixth, and dirty trans fluid. KEEP THE FLUID CLEAN!

My grandpa always said you can run trucks fast without being hard on them. Meaning, the fast changes in speed from Accelerating fast or downshifting fast is what is terrible for it. Be nice to it just like you should with any other transmission as far as making it shift but there’s nothing wrong with working it.

Sticking with OEM filters is perfectly fine. Especially the felt sump filter. Its a good one. The spin on filter (and plastic threaded insert for it) has som aftermarket alternatives. That part is up to you. Im using an aftermarket synthetic spin on as well as a metal thread (like this https://www.xtremediesel.com/revmax...MI8cS-j43X_wIVdTHUAR2CywsNEAQYASABEgJlWvD_BwE). Like I said that is your call if you want to stray from OEM. The OEM spin on is a cellulose filter (paper).

As for fluid there is nothing wrong with OEM ATF+4. Good stuff. I choose to run Redline’s fluid for the RFE. Been doing that since day one . Now this summer Im going to switch to Amsoil. Only reason for that is because the price of red line has gone up quite a lot. I’m actually switching everything I own overtime Amsoil because I save an absolute ton of money if I buy a large quantity all at once when you have the “preferred customer account”. Last order was over $500 of fluids and i save like $200 almost vs using Redline fluids.

Im also using a +2 quart aftermarket trans pan because…..well there is no downside to having more capacity. If you think about it this way, the more fluid that you have the longer it takes for that volume of fluid to become as dirty as a smaller volume of fluid in the same trans. Basic concept that a lot of guys take advantage of.

Bottom line. Iv got zero issues with my RFE and its performance. Just be nice to it. No need to abuse it or any other trans.

Hope all this helps. Im sure Iv missed some good info here but its what I could gather at the moment.

Good luck sir!!

 

[Treburkulosis]

I am at 160k. My transmission has been great. I changed the fluid at 120k. I went with Redline and a mopar filter. The pan had no shavings in it. My trans temps are 120-130 still not towing and no bypass. I dont see why it won't last until 200k.

 

[mtofell]

I don't know that I've picked up on much impact that work and tuning has on the 66RFE. Most failures I've read about on here, and both times mine failed, were under very light use and I've never tuned my truck at all. As discussed here a lot, the valve body is a weak point for sure.

As for OP's question, nobody can look into a crystal ball so it's really hard to say. Do keep in mind the old saying about how nobody comes in here to report theri tranny didn't break so I wouldn't lay awake at night worrying about it. Even with my two failures (38K and 90K miles) I realize I'm well in the minority.

 

[FlatbedHemi]

Do the bypass delete. Best bang for you buck trans mod that HELPS life span. Fluid temperature is always directly related to transmission lifespan. If it runs hot it wont last as long. Fluid deposits happen the hotter it is too.

Hot summer days (80-90F)I see 120-140 not towing whereas before I did the bypass delete minimum temp at full operating temperature was 172 or higher. Even saw 180’s NOT TOWING. The ONLY reason they designed them to run this hot is to get that fraction of a percentage better mile per gallon so they can get their EPA points. In the end, Chrysler (and all the others) is literally forced to do the stuff. I’m sure if they had a choice they would be making them without it. Part of the reason all the new transmissions use water thin fluid. My wifes ranger uses “ULV” or Ultra Low Viscosity” fluid. Stuff is insanely thin.

If I tow 5,000-6,000 lbs in the same 80-90 temps my trans temps actually still never break 140. The difference is amazing.

keep you trans fluid changes old school. Meaning no more than 30,000 miles for fluid.

I shoot for 20,000 mile intervals. I do fluid every 20,000 and fliters every other time. if you get yourself a trans pan with a drain plug and you wont have to actually drop the pan every time. Makes it a cake walk. I got an unpainted PML pan. Not all purty. Its a function over form kinda pan. Very stout. https://yourcovers.com/

Biggest things that the RFE does not like is hard down shifts, especially into fourth from sixth, and dirty trans fluid. KEEP THE FLUID CLEAN!

My grandpa always said you can run trucks fast without being hard on them. Meaning, the fast changes in speed from Accelerating fast or downshifting fast is what is terrible for it. Be nice to it just like you should with any other transmission as far as making it shift but there’s nothing wrong with working it.

Sticking with OEM filters is perfectly fine. Especially the felt sump filter. Its a good one. The spin on filter (and plastic threaded insert for it) has som aftermarket alternatives. That part is up to you. Im using an aftermarket synthetic spin on as well as a metal thread (like this https://www.xtremediesel.com/revmax...MI8cS-j43X_wIVdTHUAR2CywsNEAQYASABEgJlWvD_BwE). Like I said that is your call if you want to stray from OEM. The OEM spin on is a cellulose filter (paper).

As for fluid there is nothing wrong with OEM ATF+4. Good stuff. I choose to run Redline’s fluid for the RFE. Been doing that since day one . Now this summer Im going to switch to Amsoil. Only reason for that is because the price of red line has gone up quite a lot. I’m actually switching everything I own overtime Amsoil because I save an absolute ton of money if I buy a large quantity all at once when you have the “preferred customer account”. Last order was over $500 of fluids and i save like $200 almost vs using Redline fluids.

Im also using a +2 quart aftermarket trans pan because…..well there is no downside to having more capacity. If you think about it this way, the more fluid that you have the longer it takes for that volume of fluid to become as dirty as a smaller volume of fluid in the same trans. Basic concept that a lot of guys take advantage of.

Bottom line. Iv got zero issues with my RFE and its performance. Just be nice to it. No need to abuse it or any other trans.

Hope all this helps. Im sure Iv missed some good info here but its what I could gather at the moment.

Good luck sir!!

I’ll be quite honest. I am not up to date on this forum as I used to be on the Chevrolet forums. I really have no idea what bypass you are referring to.

 

[U&A]

I’ll be quite honest. I am not up to date on this forum as I used to be on the Chevrolet forums. I really have no idea what bypass you are referring to.

Just looked up this is one example. The OEM one has a thermostat in it and makes the trans fluid bypass the trans cooler to keep it @ 172 + degrees F.

This one wil always send the fluid to the cooler. No thermostat. Just straight thru.

https://www.amazon.com/dp/B07R24T5BN?tag=bravesoftwa04-20&linkCode=osi&th=1&psc=1&language=en_US

The bypass is located on the passenger side of your trans pan just in fron of it. It is a raw aluminum block the same shap as this with a type of E-clip quick disconnects on it.

Just be quick as fluid comes out during the switch. I lost maybe 1/2 a quart.

 

[Hemi395]

Also some trucks for whatever reason don't have this thermostat. Mine came from the factory without one...

 

[U&A]

Also some trucks for whatever reason don't have this thermostat. Mine came from the factory without one...

Oh dang…!!! Didnt know this

 

[HEMIMANN]

Also some trucks for whatever reason don't have this thermostat. Mine came from the factory without one...

You lucky rascal! When I removed mine, I was appalled at the restriction - literally a pencil thin thermostat in a 1" diameter or so oil flow line. And a crappy thermostat to boot (reports of failing closed).

Literally wtf FCA?!

 

[Burla]

Cummins and rfe doesnt match so well to be honest, if that truck is used to it's capabilities. Hemi395 has found a ton of video's on how you can address the weaknesses of the rfe and make it better. The main weaknesses are valve body and solonoid, but also some hard parts in the trans. Look up suncoast transmision for some videos on hard parts of rfe.

Product Overview: ATS 68RFE Valve Body and ATS Co-Pilot

Clint Cannon, President of ATS, describes the inherent weaknesses of the 68RFE (545RFE, too) valve body. This is a comprehensive overview of the numerous pro...

youtu.be

 

[FlatbedHemi]

Well, I ordered the filters, the bypass, and the metal thread replacement. I also ordered a new pan with a drain plug, but just sprung for the Dorman steel replacement. Its not any larger, but it was only $26. I didnt spring for the expensive deep pan mainly because changing the fluid on a high mile trans makes me nervous. I had a Silverado that smoked the 3 and 4 clutches shortly after I changed its fluid. Thats my only experience, so Im a little gun shy.

I'll be honest, I didnt pay close enough attention to the service procedures until recently because as long as I had an existing warranty, I had the dealership do my regular maintenance. I just figured they would follow the recommended factory procedures, but I dont ever remember getting a transmission fluid change at 60K. So, here I am at 125K going to do what I am assuming is the first change, just hoping that it doesnt go up in smoke like my 4l60E did. So, I opted not to spring for a $400 pan for now.

 

[mtofell]

mainly because changing the fluid on a high mile trans makes me nervous.

I've seen this argued about with many "experts" saying it's urban legend but I tend to side with you. When I was younger I killed a tranny thinking I was doing something good (tranny on +/- 15 year old car died within a few days of swapping fluid). I also had a tranny on my 99 F150 start to slip and clunk right after being talked into a "power flush" at the "Quickie Lube." I traded the truck in immediately so am not sure how that panned out.

With my 2014 Ram I stick to what the manual says for tranny fluid since I'm trying to keep my Lifetime Warranty in effect. I think the change interval is 120K but it's kind of a moot point since the trannys keep failing long before that (38K and 90K and I'm currently at 130K).

 

[HEMIMANN]

Well, I ordered the filters, the bypass, and the metal thread replacement. I also ordered a new pan with a drain plug, but just sprung for the Dorman steel replacement. Its not any larger, but it was only $26. I didnt spring for the expensive deep pan mainly because changing the fluid on a high mile trans makes me nervous. I had a Silverado that smoked the 3 and 4 clutches shortly after I changed its fluid. Thats my only experience, so Im a little gun shy.

I'll be honest, I didnt pay close enough attention to the service procedures until recently because as long as I had an existing warranty, I had the dealership do my regular maintenance. I just figured they would follow the recommended factory procedures, but I dont ever remember getting a transmission fluid change at 60K. So, here I am at 125K going to do what I am assuming is the first change, just hoping that it doesnt go up in smoke like my 4l60E did. So, I opted not to spring for a $400 pan for now.

If it makes you feel any better, I got the Dorman drain plug pan too. It's fine - you don't need more oil if you keep that temperature down where it used to be before they started putting in a too small thermostat orifice!

 

[U&A]

You lucky rascal! When I removed mine, I was appalled at the restriction - literally a pencil thin thermostat in a 1" diameter or so oil flow line. And a crappy thermostat to boot (reports of failing closed).

Literally wtf FCA?!

100%

iv still got mine.

Ima go get a pic

 

[U&A]

Well, I ordered the filters, the bypass, and the metal thread replacement. I also ordered a new pan with a drain plug, but just sprung for the Dorman steel replacement. Its not any larger, but it was only $26. I didnt spring for the expensive deep pan mainly because changing the fluid on a high mile trans makes me nervous. I had a Silverado that smoked the 3 and 4 clutches shortly after I changed its fluid. Thats my only experience, so Im a little gun shy.

I'll be honest, I didnt pay close enough attention to the service procedures until recently because as long as I had an existing warranty, I had the dealership do my regular maintenance. I just figured they would follow the recommended factory procedures, but I dont ever remember getting a transmission fluid change at 60K. So, here I am at 125K going to do what I am assuming is the first change, just hoping that it doesnt go up in smoke like my 4l60E did. So, I opted not to spring for a $400 pan for now.

I get it,

Totally do.

IMO its a risk as well. 6 in one 1/2 dozen in the other. Kinda a d@med if ya do dmed if ya dont kinda thing. You know man, I am absolutely not trying to tell you what to do. Just sharing experiences.

If the trans does that after a fluid change its probably not gone have much of a long life anyway.

Pics of the thermostat bypass. Measurements curtesy of my favorite tool in my tool box. My Starrett square.

Image KM-93

ohvrlee.sharing.bublup.com

And here it is. Tiny A$$ hole on the thermostat side.

Image KM-95

ohvrlee.sharing.bublup.com

 

[deputy25]

The thermostat on my 2018 went bad yesterday. We had just left for a camping trip pulling our travel trailer (7800lb) and 5 miles from home we got a trans temp light and the truck went into limp mode. We pulled over and let it cool, I checked the lines with the heat gun we check our wheel bearings with. Truck is running fine if we aren’t towing (150-160) but gets hot quick with a load. It is still under warranty so we will prob replace the stock part. As soon as it’s out of warranty we will install a bypass.

 

[U&A]

The thermostat on my 2018 went bad yesterday. We had just left for a camping trip pulling our travel trailer (7800lb) and 5 miles from home we got a trans temp light and the truck went into limp mode. We pulled over and let it cool, I checked the lines with the heat gun we check our wheel bearings with. Truck is running fine if we aren’t towing (150-160) but gets hot quick with a load. It is still under warranty so we will prob replace the stock part. As soon as it’s out of warranty we will install a bypass.

Personally, I would look for a bypass that looks like the OEM, just raw aluminum. If not, I’d buy one and then spray paint the darn thing silver. Let it dry. Throw some dirt on the dang thing and they will never know.

 

[2020PW]

It’s all about preventive maintenance, change the fluid on a regular basis and you will be ok. Regular bases is 30-40k if you’re towing, etc. Owners manual says change it every 60k if your towing, etc.

Larger tires would be considered towing, Etc.

 

[Andersoncma]

My wife’s uncle just bouth a 3rg gen cummins and not a month later the transmission pooped out on him. Truck had around 150k. They took it to a reputable repair shop and they said nothing good about that trans. They also said “They ALL”, meaning any Dodge transmission, go out around 150-180k, “if you work them”.

My truck has the 6.4 and the 66rfe, running 35” tires, steel utility/hay spear flatbed, with about 125k on the clock, that is my work horse on the weekends, and I started getting concerned. So, I got online and started doing research. I have seen more than a few posts about the 66rfe and its problems. However, I also got to wonder if having the truck regeared would help save the transmission. My truck has been running 4.88s since 75k miles, which is about when I started really working it. So, while I’m sitting here wondering how much life my transmission has left in it, I saw where someone posted and pointed out that you only see the problems when you search online, so you never know how many are out there running problem free.

So that got me to thinking, how many 66rfes are there running high miles problem free?

How many people have had problems even though they modified their drivetrain?

How many miles was on it when the trans died?

I think your odds of a successful service life w this trans is keeping trans temps at bay. I have 195K on mine and have never had any issues. I did install an aftermarket trans cooler with fan (in addition to the factory cooler). Whenever my truck is on the road it is always loaded to about 11K lbs gross (it’s a Ram2500), but will often be hauling close to 18K gross for shorter distances. I drive it easy, but given its history so far I expect that trans to last as long as I have the truck. One other issues this trans was a clunking sound when I put it in gear. I figured that out and the hard clunk went Away. I figured out where this trans likes the fluid level to be on the stick…hence, I also installed a drain plug in my pan so I could tweak the level of fluid just perfecrly