Couple of months ago I replaced the transmission in my truck. From the start it seemed to be running hotter than the bad transmission I pulled out of it. Mechanic friend said it was normal for it to run hot while breaking in. Never heard of that, but I'm not a mechanic, so ok. A few weeks ago I was going down the interstate at 70mph keeping an I on the tranny temps. Was running hot, 177f as it's been doing. All of a sudden in a matter of a few minutes it dropped 15degrees. Ran cooler for a few week after that until today when it got to 204f. I was again going down the interstate unloaded. Slowed down to 60mph and it slowly came down into the 190s, it also started raining so that helped to. This is a local reman transmission, new 6.0 cooler installed in the OEM cooler location, radiator and lines were flushed, inline filter placed after to cooler in the return line. After getting back home checked things out. Cooler lines coming from and returning to transmission were hot, but not incredibly so, could touch. Transmission was very hot, bypass was very hot, much hotter than cooler lines. Could this be a bad bypass and how could I check?

 

I would suspect a stuck bypass valve. They're not to expensive IIRC

 

Ordered the Sonnax rebuild kit. Hope it does the trick.

 

Ok, None, of those temps mentioned are hot. @Mark Kovalsky Has stated it can run 220* all day long, 250* for short periods (IIRC) and you want it to hit 170* for a period to deal with any condensation.
My 4r100 runs 170-190* depending on the ambient temperature, towing weight and particular elevation I’m towing at. Im in Colorado at 6000’ and tow a 9000k pound fifth wheel. I’m also running a 6.0l cooler and a Derale fluid thermostat. There could be an issue with something but those temperatures are well within normal operating temps.


Derale 25792 Fluid Control Thermostat Kit

 

My concern was it went up to 204f unloaded on flat here in Florida going 70mph while the ambient air temps were in the lower 90s. Didn't seem right. The old tranny, even on its way out didn't run that hot.

 

Those transmission temps do not sound right to me in an unloaded truck on flat ground with a 6.0 cooler. I tow 10-19,000#'s up hills throughout the day and only once seen my gauge above 200*. You can eliminate the bypass valve on the transmission. Not sure I can offer any advice other then my transmission temps towing up hills are generally lower then yours are empty on flat ground with the 6.0 cooler.

 

That's a little higher temps than I would expect. Since your bypass line is hotter than the cooler lines I suspect the bypass is leaking. The rebuild kit should fix your problem.

 

Thanks, Mark, for chiming in. I'm hoping that it fixes it. I really don't won't to pull the transmission I just put in. Figured I will rebuild the bypass and then do a flow check on the return line. Any other advice you can give?

 

@Mark Kovalsky Can you address the post right above yours about removing the bypass.

 

One other thing it could be is your torque converter is unlocking in third or forth gear. Try goosing your truck in forth gear and see if the tach jumps several hundred rpm's. Had this happen to me recently and had the same symptoms.
Real easy fix.

 

It isn't a good idea to delete the bypass. The bypass is there to protect the rear half of the trans if the cooler circuit becomes restricted. Without the bypass if the cooler circuit is restricted the rear half of the trans runs without lube. The bypass maintains lube flow if the cooler circuit is restricted.

 

Subscribing....
Is it safe to turn the ride off with temps hovering 190*-200* ish?
Was in Vegas all last week, with the clusterf@$k that place is, i noticed my temps more elevated than ive ever did...
B.G, do a how-to buddy, on that Sonnax, if you dont mind. Mines' collecting dust because the horror story of The Brad's misfortune

 

Now you have me worried. What happened to The Brad?

 

You can run all day long at 220°F with no problem. 200°F is well within the normal range. That isn't hot, it's normal.

 

Coincidentally, I found this post from Mark K a while back while populating the new 7.3L PSD Tech Folder...


https://www.ford-trucks.com/forums/1...l#post17291624