Hi folks.

I've been fighting an overheating problem in my 2002 Ex (7.3L, 4R100) for quite some time. When I bought the vehicle new, it had the stock 7.3L cooler on it, as well as an aftermarket cooler in front of the AC condenser.

After fighting to tow up mountains with a car hauler (trailer 1800lbs, car 3000, tools & people @ 2000), the trans temp would regularly get "high". I say "high" since I didn't have a Scangauge.

After adding the gauge, I got a better feel for driving it and trying to keep it cool, but slow towing (30-40mph) up mountains is just too much for it - I would have to stop and let it cool down every 1/2 mile or so and only drove it until the temp would hit 240.

I swapped in the 6.0L trans cooler for the 7.3L and still had the same issue.

Multiple fluid flushes, some debris in the pan. I then swapped the torque converter.
Still having issues towing up hills slowly or in traffic. Stop and go traffic is killer and will regularly see 200F+ on flat grade.

Just last night, I personally flushed out all of the coolers at 15psi (confirmed NO blockage), and put in the fancy external trans cooler w/ pressure gauge to ensure that things are going well (http://www.dieselsite.com/1999-20037...tersystem.aspx). Post swap, measured pressure is 15psi on the lines.

Here's my question - after driving around for 30 mins unloaded, flat grade, I see on my Scangauge that I'm reading say, 170F (when it's 80F ambient), and I hop out and use my IR thermometer to measure the temp coming out of the external filter @ 115F - a delta of 55F. What should the temperature be reading? And where does the Scangauge read the temperature from? Outlet of the trans going to the coolers? Internal temp? Return temp? I think it's PCM temperature, but I don't know where that is in relation to the cooling circuit.

I'm just trying to figure out how to push the vehicle and whether a reading of 250F is really 200F or vice versa.

Additionally, I see that the cooler lines running from the transmission appear to go into the radiator at the bottom passenger side - I'm assuming there is some loop in there and it's not just a straight passthru (eg, OTW?)

Does anyone have a cooler diagram for this setup?

Thanks for the collective wisdom folks!

 

The stock cooling system goes from the outlet at the front of the trans to the OTW cooler in the radiator. From there is goes to the air to oil cooler, then returns to the rear of the trans.

Do you have three coolers? I can't be sure from what you wrote. If so, you probably have too much restriction which will open the cooler bypass. This allows most of the cooler circuit flow to bypass the coolers.

The PCM reads the temperature from the Transmission Fluid Temperature sensor on the solenoid body inside the transmission pan.

Normal temperatures not towing are 60-100°F above ambient temperature. 170°F is ideal. Anything below 220°F is fine.

I don't see how you have confirmed no blockage in the cooler circuit. Blowing air through it doesn't confirm anything. Here is how to really check:

Warm up the trans by driving until it is at least 150°F. Have two one gallon containers handy. Remove the cooler line where it attaches to the rear of the trans. Point the line into the first container. Have someone start the engine, leaving it in park and the engine idling. Once the flow is steady move the line to the second container for exactly 15 seconds, then put it back in the first container and shut the engine off.

If fluid sprayed out of the transmission where the line was removed it fails the test. If there is less than a quart in the second container it fails, too.

 

Current setup (based on your assertion): OTW, 6.0L cooler, and some generic cooler. Should I bypass the front (aftermarket) cooler?

If the bypass was opened, I should see ~0psi on the return trans coolant line, right? Currently, I'm seeing 15psi on the new setup.

I can try to duplicate the test this weekend, but assuming it's working fine - is this just normal operation?

Other thoughts?

 

I would delete the aftermarket cooler.

The bypass is going to open until the pressure drops below it's setpoint. The valve will end up regulating to a pressure. 15PSI might be it, I'm not sure.

 

Mark, from doing some digging around here, I found a post (from you, interestingly enough) that covers some of this:

https://www.ford-trucks.com/forums/1...l#post12133590

In short - 10-20psi at idle is expected, and if the flow drops to <5psi, it should open the bypass. So at 15psi at idle through the filter, I think that it's okay?

I'll still look into removing the front cooler.


Any other guesses from the community at large?

 

Mark if fluid comes out of the return port on the trans during this test what causes that ? I know it's not good. Just looking for knowledge.

 

It happens when the bypass is open. That can be caused by a stuck bypass valve or a restricted cooler circuit.

 

It seems that Torque can read both "Transmission Temperature" and "Transmission Fluid Temperature" from the PCM. (PIDs 2211bd and 221674).

In my truck, the value for the Transmission Temperature has typically been 5 - 10 degrees hotter than the value for the Transmission Fluid Temperature.

In trying to understand this difference, I was hoping to understand from where the PCM was getting its data. Stated differently, assuming it exists, where is the transmission temperature sensor located?

I believe there is also a PID for transmission line pressure (2211c0). If my understanding is correct, where is that sensor located? Could it be the bypass? What is the appropriate transmission line pressure (which at idle I'm guessing is the equivalent of 1 liter per 15 seconds, but under load may be higher).

Thank you.

 

The PCM reads the temperature from the Transmission Fluid Temperature sensor on the solenoid body inside the transmission pan. There is only one sensor.

There is no sensor. That's a calculated value of what the PCM wants for line pressure.

Here is what line pressure should be when measured at the test port on the side of the transmission.