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Discussion Starter · #1 ·
2001 F-250 Extended Cab, 7.3L, 4R100, 140K

I have had this truck since 2003. I rarely tow but almost every time I do I run into an overheating problem and fluid pumping out past the front pump seal. I am usually towing over 10,000 pounds, This has only happened when I get off the highway and have to do some stop and go driving. I can go for hours on the highway in 100 degree weather with no problem. This problem persisted even after installing a large Tru-Cool cooler a decade ago. I forget the model but it is about 8"x 24". I never have this problem when not towing.

Saturday I pulled the transmission to replace the pump seal. This turned into a much bigger job than anticipated when I found a large snap ring loose inside the transmission. I ended up having to disassemble much of the transmission to take of the snap ring issue. Loose snap ring in trans. Recommendations needed.

Monday morning I finished getting everything back together. Everything looked to be in pretty good condition. The TC looked good with no signs of overheating. While I had the transmission apart I added most of the parts from a Transgo Tugger kit, and enlarged the pump oil return passage between the bushing and the front seal. I took it out for a drive and honestly I did not notice any difference in the transmission. What I did notice, now that I have a scan tool was that my internal temperature rapidly approached, and then passed 100 degrees centigrade. ( I do not have any transmission temp gauges in this truck.) T he transmission pan indicated about 20 degrees cooler than the scan tool reading when measured with an IR thermometer. The outside air was only about 85 degrees Fahrenheit.

This was not good. I came home and did some more research. I ordered a new cooler bypass line from Ford. I picked it up and installed it this morning. I went for a drive and the results were not any better. I put the truck back on the hoist and started looking at all of the lines. The lines to and from the Tru-cool were as they were supposed to be. I looked at the line from the transmission to the liquid cooler. It seemed to be poorly routed behind the stabilizer bar. I puled back the chafe guard and fond that the rubber hose had a significant kink in it. (See before and after photos below. The kink looks worse in person.)

I put in an order for a new assembly. It should be in tomorrow morning. In the mean time I rerouted the old assembly in front of the stabilizer bar, where it is supposed to be. I took it for a drive and saw a definite improvement. Still not where I would like it, but about 10 degrees cooler at the pan, and 21 degrees cooler on the scanner, with the OAT 10 degrees warmer. There still may be some restrictions in this line and I am hoping a new one will yield even lower temperatures.

I am curious about the difference in temperature readings between the pan temperatures and the internal temp read on the scanner. I believe scanner data comes from the solenoid pack. I know on many piston aircraft engines the oil temp is read after the oil cooler. I suspect the solenoid pack temp may be before the cooler and the pan fluid is after the cooler. Regarding acceptable temperatures, should I be looking at the pan fluid temperature or the solenoid pack temperature?

I ran the truck for at least 25 minutes. Much of it in first and second gear trying to get things hot. The temperatures peaked and were steady when the readings were taken.

Before rerouting line After rerouting line
OAT 80 degrees F OAT 90 degrees

Scanner temp 231 degrees F Scanner temp 210 degrees F

Pan temp 195 degrees Pan temp 186 degrees

Eng coolant 156 degrees Eng coolant 162 degrees


I have no idea how the line got routed behind the stabilizer bar. The kink was definitely restricting the flow and I suspect it may still be restricting it to some extent. The new assembly should fix this. Just one more thing to check when you have a cooling problem.

John


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Discussion Starter · #2 ·
Yesterday I did a cooler flow test. It ended very quickly as I was bypassing fluid. (The bypass tube is brand new) I will have to do more trouble shooting next week as I am headed out of town today. This morning I checked the trans temp after it had been sitting all night. It reads 26.32 degrees Celsius, that is 79.4 degrees Fahrenheit. The OAT is 65 degrees F. So the trans is reading 14 degrees F high via the internal sensor. I think the first thing to try is bypassing the factory OTA cooler and just use the water and Tru-Cool OTA cooler.

My departure out of town had been delayed so I plumbed in a pressure gauge into the cooling circuit. I did this up front just aft of the radiator. On the return line, just before the hard pipe, it only shows about 9 PSI. This is with the fluid going through all the coolers and the bypass bypassing fluid. After the radiator water cooler I measure 25 PSI. Bypassing the factory OAT cooler I get 15 PSI. Thus the factory OAT cooler is adding 10 PSI of back pressure in the system. Does anyone know when the bypass tube on the side of the transmission starts bypassing?

I am going to bypass the factory OAT cooler and go for a drive.

Just went out and drove for 30 minutes with the factory OTA cooler bypassed. Lots of stop and go. Empty truck. Tried to work it as much as I could. Trans temp was 150F when I started.

OAT 90 degrees
Scanner Trans temp 210 F (Peak)
Pan temp 174 F (IR thermometer)
Cooler line out near trans 175F (Return and outlet lines measured with calibrated HVAC Clamp on probes.)
Cooler return near trans 135 F
Tru-Coll inlet 135F (IR thermometer)
Tru-Cool outlet 115F(IR thermometer)

Have to pick this up next week when I get back.

Photo of pressure after the radiator cooler and before the factory OAT and the Tru-Cool coolers. Bypassing the factory OAT cooler lowered the pressure by 10 PSI.
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Discussion Starter · #4 ·
I drove it around with the 25 foot trailer behind it for half an hour. A few hills and lots of stop and go. The pan showed about 100 degrees above ambient. I still have the factory oil to air cooler bypassed. Just the radiator cooler and the Tru-Cool upfront. I will find out Thursday. I have about 800 miles to go with lots of big hills in the middle. The kinked hose, along with the restriction in the factory OTA cooler were likely a big part of the problem in the past. Hopefully fixing these problems, along with the front pump seal will mean the end of high temperatures and fluid leaks past the front seal. I'll know more by Thursday night.
 
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