Hi all,

This is my first 7.3 of this generation so I'm really not familiar with what's normal and what isn't. Is this stock? There are a couple unconnected hoses near the passenger side headlight that are currently loose at both ends. Before I remove them, I'd like to confirm what they were there for. Thanks in advance for the answer

 

That's an aftermarket trans cooler. The stock one is tiny and looks like it was removed. The radiator has a cooler in the bottom which is important to be used. Its water to water cooling where the one you see is air to water. Both work together for proper cooling of the trans. Why the lines are disconnected, IDK.

 

I was going to mention that the bottom part of the radiator had been deactivated... it's not used and the hoses that should have been going there are probably those disconnected ones. So this aftermarket air/air cooler is the only transmission cooling available in my truck's case as it's currently set up.

Out of curiosity... if this air/air cooler is larger than the factory one, surely there's a point in size where an air/air cooler would match then exceed the original heat dissipation output of a tiny stock air/air + bottom of the radiator... this one might still be way too small, but still...

I recall the connections at the bottom of the radiator were pretty rusted out, the previous owner probably found that was leaking so he went ahead and added a larger trans cooler hoping it would do the job alone.

 

Here's a pic from when I pulled the radiator out, not long ago.
I immediately assumed the disconnected hoses should've been doing to those two rusty connections and that the air/air trans cooler in front of the radiator had been added as a replacement.
Are the rusty 'nipples' built in, or can they be replaced? If I recall correctly, one of them was even partially broken.

 

If I were to try to go back to setting things up like that, I'd route the hose to go from the trans to the radiator first (get down to the operating engine temp) then to the air/air cooler (to now use the ambiant air temp), right? I might have a few questions later about that - to make sure I know which connection to the trans is the "out" and which one is the "in".

Thanks in advance

 

If you are sitting in traffic the bottom of the radiator is important to keep the trans cool, the air to air one doesn't get enough air. The bigger cooler that replaced the factory one is still to small if you tow at all. The stock one is a joke, I heard some use it for a power steering cooler if you have bigger tires.

I'm not sure but I don't think the rusted connections can be replaced. That's a pretty good hit the radiator took!

If I remember correctly the line going to the rear of the trans is the return line. Yes, run them to the radiator first, then to the air to air second.

 

The transmission circuit is completely separate, right? i.e. that bottom part of the radiator is isolated from the rest of it.

Most of my vehicles have been manuals, and I'm realizing I never paid any attention to transmissions' cooling circuits. Does it have its own water pump? Where do you fill it up with coolant? Is the coolant reservoir feeding both systems by gravity...?

I'll take the radiator out and inspect the two connections for the transmission cooling part of it more carefully, see if they can be saved.

Thanks so much for all the info so far, oldbird1965!

 

Another question - the radiator part, is it perfectly symmetrical in there? If so I can connect it either way, but otherwise, I have to find which of the two rusted connections is the inlet and which is the outlet.

My air/air cooler seems symmetrical, but I guess I'd tend to have the entry at the top and exit at the bottom, gravitationally speaking, even though the amount of pumping needed should be the same either way.

 

No, it is not. The transmission cooler is cooled by engine coolant. After the radiator has removed the heat from the coolant it flows over the transmission cooler.

No, it does not have it's own water pump. The engine's water pump circulates the engine coolant and the transmission pump circulates the ATF.

Yes, it is.

They are also symmetrical.

You didn't ask, but the cooler in your photo is not a good cooler at all. It is a tube and fin design, just one tube the criss crosses with some fins attached. It's very inefficient. A stacked plate design will remove a lot more heat than that one will.

 

I already thought pretty highly of this forum, but having a Ford Automatic Transmission Engineer answering my questions personally is about as good as it can possibly get! I feel really spoiled and will try to return the favor as time passes by making sure I remain an active user and help others when I can.

Actually, this was a bit of a brain fart moment on my part - I was operating under the stupid assumption that the transmission was getting cooled by coolant, while in fact it should have been pretty damn obvious to me that it's the ATF that needs cooling. Given that the rusty connections have been left open and that nothing's been leaking out from the radiator from them, I had to conclude whatever coolant was supposed to flow through those had to be a second coolant circuit, but now of course the answer's obvious - the ATF is the liquid meant to flow through those, and it obviously had its own circuitry in there (which has been sitting empty and accessible by outside air) to exchange heat with the same coolant as the engine without mixing with it. Very logical and thanks Mark for setting me straight (I'm sure oldbird65 would've done that too, but you were faster than him)

Makes perfect sense. When reconnecting things properly though I will likely spill some ATF, and will probably need to add some anyway (longer hoses when I'll be done). Would you be kind enough to confirm what oldbird65 said about which transmission connection is the outlet of ATF and which one is the return of the cooled fluid? I suppose I could start the truck and see which of the two hoses spits ATF (I may have to shift into Drive for this to happen, or would it circulate even at Park?)


Great idea. I actually have a spare FPHE I used during the two years I ran my Chevy on WVO... I could replace that cooler with it. Although that would require a bit of modification to the coolant system, while an air/air cooler does not. It's a basic FPHE, two inlets and two outlets, meant for liquid coolant.

The previous owner of this truck spent the last few years opening his big yard and driveway with it - the truck had no tags, the transfer case stayed in low range all the time, and the transmission would only operate in temperatures below the freezing mark. I'm guessing even a subpar setup was enough for him in those conditions.

 

Don't forget the Former tag in front of my title. I left Ford 11 years ago.

The front connection is out to the coolers, the rear is the return. Fluid will circulate anytime the engine is turning, regardless of what gear the trans is in, including park.

 

Yeah, I know, but that's actually even better from our point of view in this section - for advice and information on 1990s E4ODs, you're likely an even better source than the average current Ford engineer


Great, thanks!
Also, I immediately realized after posting above about my flat plate heat exchanger that it can't be a true replacement for an air cooler, given that it will only lower the ATF to the coolant temperature, no further. It's great for WVO, and it's also my "Plan B" if I can't use the radiator connections because they're too damaged, but it won't help get the ATF's temperature any lower than exit coolant at engine operating temperatures - unlike an air cooler, which I gather is needed to supplement radiator cooling precisely for that reason.