99 Expy, 5.4L, with tow package

I installed a larger transmission cooler (https://www.ford-trucks.com/forums/1...r-install.html) awhile back and towed our TT to Destin, FL last week. Several times during the trip, I turned off the AC and discovered that my transmission temperature would decrease 5 -7 degrees within a few miles. I believe it is the heat from the AC condenser affecting the transmission cooler. Below is a picture of the new cooler sitting in front of the condenser.



The new cooler is about twice as tall as the stock transmission cooler and I installed it in the same location as the stock cooler so it sticks up higher than the stock cooler. Also, the stock cooler was installed at an angle. It angled out toward the front of the truck (see picture). The new cooler sits straight up.



This is the only explanation I can come up with for the AC affecting the transmission temperatures. Does it seem like the condenser could have this big of an affect on the temperatures?

 

Your conclusion is wrong.

Running the AC simultaneously places a greater load on the engine (it works harder - more heat in the radiator) and the heat rejected from the condenser is slightly raising the temperature of the air flowing through the radiator reducing its efficiency. Since the stock plumbing for the transmission cooler circuit runs through the radiator, the transmission isn't cooling quite effectively.

In all, if the temps only rise slightly and stay within the normal operating band, don't worry about it.

 

The condenser is in front of the radiator, is it not? Now you have an oversized tranny cooler and a condenser for air to pass through before it even reaches the radiator. This setup will make for higher coolant temperatures in the radiator. The radiator also contains a built-in tranny cooler. So as the tranny fluid (which is now a lower temperature than the coolant) passes through the radiator, it absorbs heat and take it out of there, resulting in an increase in tranny fluid temperature.

 

Ok, that sounds reasonable. I knew the transmission lines ran through the radiator before the cooler, I just didn't think running the compressor would put that much more of a load on the engine.

The transmission temperatures are fine. It hit 204 while in stop and go traffic. Out on the interstate pulling at around 60 mph it ran between 195 and 200. This is with the outside temperature in the low 90s. We ran through a couple of rainstorms and the transmission would run between 175 and 185. With the stock cooler, it had hit 215 in stop and go traffic and would run between 208 and 212 on the interstate.

I don't recall if the transmission temperature would drop when the AC was turned off with the stock cooler. I assume it would.

I guess if I'm ever running too hot with the AC, I can help things out by turning off the AC.

 

That new set up bothers me. It is the zip ties and how you fastened it down. Looks like you routed them through the condenser and radiator and zipped them up. Not really a good idea. There is a good chance that the fins in the radiator/condenser will free up and allow movement which will in turn cause wear and could wear through the condenser/radiator and cause a leak. That is why Ford mounted it in front of the condenser on its own mount. You could be asking for problems there. Is it metal on metal or did you put some foam tape separating the trans cooler from the condenser?

 

I think maybe the pictures aren't showing it very well. I have a detailed post of the transmission cooler install with many pictures (https://www.ford-trucks.com/forums/1...r-install.html). The transmission cooler has 2 L-brackets on the bottom that are mounted into a support below the condenser (see pictures in referenced post). The stock cooler was also mounted to this support via an L-bracket. There is also an L-bracket on the right top of the cooler that is mounted to a vertical post that runs in front of the condenser (again, the stock cooler was mounted to this vertical post via a bracket). The cooler sits about 2 inches in front of the condenser. There are zip ties on the top left of the cooler, but they do not pass through the condenser or the radiator. They wrap through a vertical post that sits at the midpoint of the front of the truck about 3 inches in front of the condenser. Again, the stock cooler was mounted to this vertical post via a bracket with multiple bends. I did not have the capability to make a bracket to mount to this post, so I opted for zip ties to simply provide some front to back stability (although, even without the zip ties the cooler is securely held by the 3 L-brackets).

The cooler sits about 2 inches in front of the condenser and does not contact the condenser. The L-brackets and zip ties mount to posts/supports that were also used by the stock cooler.

 

I tried doing a search and either I did not do it correctly or there is nothing on here about this. Is there a write up or some thing about hooking up a trans temp gauge to the test port. Any pictures ect. I would like to install a temp gauge and I think using the test port would be good. Thanks for the help.

 

I installed the sending unit in the test port on the drivers side. Here is a link to the article I followed (TheDieselStop.Com - www.thedieselstop.com). It is for a 1999 SD, but it was the 4R100.

 

Thanks for the help.