The pan is receiving fluid that returns from the cooler. That will be the coolest location in/on the transmission. The sensor that the Scangauge is reading is on the solenoid body, and that is much warmer than the pan.

If the bypass is not working properly the coolers and cooler line will not be very hot because a lot of the hot fluid isn't going there.

Fluid level is pretty sensitive. Add half a quart at a time.

 

So, all in all, I’ve replaced the stock transmission cooler with a 6.0 cooler, changed the filter and fluid using synthetic (the old filter and fluid still looked clean/red), completed the flow test, and now I’ve finished “rebuilding” the bypass valve. After a 20 minute drive unloaded with only me in the truck, the temp was 192. Ambient temp right now is 88. The fluid level seems to be correct. Even after 10 minutes of idling in the driveway, the temp has only come down to 186. I haven’t even tried to tow again because my empty temps seem excessive so I don’t have any data for that.

By this point, it seems I have 2 options.

1. Accept the fact that my transmission has internal damage that is causing it to run hot.

or

2. Accept that the people claiming 170 towing 10k are exaggerating and my truck is “normal”.

If I have a 3rd option, I’d love to hear it. A new truck isn’t really an option, but neither is a new transmission.

Many thanks to those of you that have given input. I realize that none of you know me and there’s no meaningful way for me to return the favor, so I really do appreciate the time/input.

 

Does your trans fluid run pressure from the transmission into the radiator, from the radiator into the transmission oil cooler and back to the transmission?

 

Yes, I just confirmed. The line goes from the front of the transmission, into the radiator on the passenger side, out of the radiator on the driver’s side, then into the 6.0 cooler, then out of the 6.0 cooler and into the back of the transmission. The outside of the lines show no visible signs of damage and the hoses for the cooler aren’t kinked.

I’m still curious about the higher than ambient temp readings upon startup. I’m going to install a standard trans temp gauge and compare the readings and see if the Scangauge is giving me a bad reading. I’m not hopeful, but it will at least rule out that possibility.

There has to be something I’m missing. Fortunately I’m working from home and we aren’t going camping until maybe Labor Day so I have some time to mess around with it.

 

Here’s the latest: I just installed a traditional gauge (Glowshift Trans Oil Temp) in the test port. The truck has sat for about 24 hours without running. Outside temp is 93. Upon startup, the Scangauge showed 122 and the Glowshift showed 97. After about 10 minutes of idling for a leak check, the Glowshift showed 108 and the Scangauge showed 144.

I realize the temp readings are coming from two different points in the trans, and the Scangauge will show a higher temp because the OEM sensor is in the solenoid pack or somewhere deep in the jungle of transmission guts, but I’m going to have to assume that the OEM sensor is simply showing an incorrect temp. I’ll be driving the truck at least 30 miles tomorrow including some stop and go, so I’ll see what the max temp is, but so far it’s gotten all the way to 205, water temp was 199 in the drive through (on the Scangauge).

My gut tells me that the readings I’m getting from the Scangauge are inaccurate. At a minimum the low temps are off and that can be verified. Obviously nobody on here can see the truck or drive it, but does my logic seem sound?

Are there any repercussions to driving with a bum temp sensor?

Also, if anybody is considering it; the Glowshift universal gauge pod is not universal. It does not fit the early super duty.

 

Are you referring to the A-pillar pods they sell?
If so, that sucks for my plans, unless you were trying to replace existing A-pillar molding when GS's pods are designed to fit over existing molding.

 

What is the Sonnax kit? The only thing that comes up are automotive cleaners.
I have a 2002 F250 7.3l Diesel, the only time my trans overheats is towing 10,000 lbs on a steep grade like the New Priest Grade going to Yosemite or if I am forced to slow down on a grade and the torque converter unlocks.
I have the Mishimoto trans cooler but have not installed it yet. I'm waiting until the 100+ temps go away.

 

I’m pretty sure the custom fit pods work fine, but I couldn’t find a single gauge pod with a 52mm hole that the trans temp gauge requires, so I ordered the universal. It fits over the stock trim, but would need to be screwed in to stay in place. It doesn’t snap in or anything and I don’t want to put screws in it.

 

The Sonnax kit is a trans cooler bypass valve rebuild kit. It was $17 and took about 20-30 minutes to install.

 

I ran the truck for a while yesterday and the Scangauge reads a consistent 35-40 degrees higher than the Glowshift gauge reads. The highest it got was 167 on the Glowshift and 205 on the Scangauge. It was 95 degrees outside.

Mark, if you’re still around, is there a trans temp for the 4R100 that should alarm me? I’ve seen some guys posting 250+.

Knowing now that the 235 that I saw in the mountains at 20 mph on a 7% grade was probably only 195ish on the Glowshift makes me feel a little better about the health of my trans. I definitely need to change that seal out, but that can probably wait until my next fluid change. FWIW, my stock gauge never budged during that trip.

 

You can take a 4R100 up to 220°F all day long with no problems. You can go as high as 250°F for up to a half hour at a time.

 

That’s reassuring. Thanks. And thanks to everyone else that gave input. I appreciate the help.

I guess long story short is, different temp sensors will give different temps!

 

Thanks for the link.