So after burning up and destroying a transmission, I think the problem is inadequate flow through the cooler lines and coolers. How many PSI of pressure should it take to blow fluid through two cooler lines and two coolers (the radiator one and the factory external one)? I think I don't have enough flow.
Has anyone bypassed the radiator cooler and just used the factory auxilary cooler on a '78 F250? Truck will be driven in the summer time only....no winter driving.

 

It shouldn't take much pressure at all if the ends of the line are open. You should be able to blow through it with your mouth (through a clean length of hose naturally).

Running an external cooler only is fine as long as it is a big one. A little auxiliary cooler alone would not be enough.

 

Blue and White, I did just as you suggested (blowing through a clean length of hose) and I pretty much turned blue trying to force the fluid out. A restriction I guess? Just for fun, I did the same thing with the hose connected to a pressure guage. couldn't get the needle to go about 2 psi when I"m almost turnign blue in the face lol faulty guage or is that all the human lungs will produce...2 psi? mmmmhhhh

 

Maybe you will get 3 psi with your cheeks only, no lungs.

It sounds like its pretty well plugged.

 

Trying to blow through a cooler and lines filled with oil is a whole different story than trying to blow through a system that is empty.
If there is no oil in the cooler and lines you should be able to blow through it fairly easy. If it has oil in it I doubt you'll blow through it at all. You may be able to get the oil to dribble out but that's about all.

 

mike, ya i barely made it dribble, but then i didn't get out much oil when i finally heard air coming through. I think I'll take each piece apart (lines, ext. cooler) and blow some low pressure compressed air through them just like i did when i "flushed" them out with brake clean prior to assemby. Maybe it's the cooler in the new radiator that is partially plugged - i never tried to blow through that before assembly...it's new right.....it should work.....

 

use a compressor to clear the lines. I can register 7 psi on a gauge just with my lungs. lol. You should be able to blow through it once you clear the lines. I am using a medium sized external cooler in front of my radiator for my transmission. I do not like the factory kind because whats your coolant at? 190 degrees or so? 230 when its hot. you want your transmission temperatures under that, ideally. Nice to keep them around 175 if possible, under 200 at all times.

 

hesteranger, ok maybe my guage is not calibrated correctly haha. I have been thinking the same thing about why the transmission fluid goes throught the "hot" radiator first before going to the factory external cooler. What I'm thinking is just using the external factory cooler only and bypass the radiator one. Think the factory auxiliary one is big enough by itself to cool the fluid? I'm not planning on doing an towing of any kind (collector car insurance forbids towing ;( ). I do run 35" tires but that shouldn't overheat the tranny too much I wouldn't suspect. Any thoughts?

 

bypass the radiator?

Wrong move. The system does more than cool the transmission fluid. First it helps to bring the T fluid up to operating temps quicker. Then later what you think as "Hot" is in reality still cooler than the T fluid. After transferring some of that "hot" to the cooler lower radiator it helps the external cooler do a better job in supplying the trans a relatively cool fluid; and the cycle repeats.... A simple engineered system which works.

.

 

Thanks for the input guys. In my quest to figure out why the trans fluid got burnt, I pretty much disassembled all 4 pieces of the cooling system and was able to blow air with my mouth through them. I'm pretty sure the cooling system on the truck is A OK, just waiting to see what the transmission shop is going to tell me as to what caused the fluid to get too hot and have the transmission destroy itself. I think i'll keep the whole system intact for maximum cooling.....there is a reason Ford designed it that way i guess.

 

it does bring the transmission fluid up to temperature when its cold, but if you ever put a gauge on your atf it comes up to temp pretty quickly, even when its chilly out. I know its a diesel, by my excursion gets the trans fluid up to temp before it even opens the thermostat....

the factory aux cooler isn't big enough to handle the trans by itself. It does an ok job of cooling the trans fluid to below the temperature of the coolant after the radiator has theoretically cooled it to near the temp of the coolant.

 

Update: Before I install the rebuilt tranny again, I wanted to verify that the coolers were clean and free flowing so I don't have to go through all this trouble again. What I did was disassemble all lines and coolers. Both steel lines are free - no question there. What I did to the coolers was hook up my siphon gun and a gallon of brake / parts cleaner. Instead of "blowing" the cleaner through the coolers, I used the siphon gun to "suck" the fluid through. I was able to get fluid to come through, but certainly not at a steady full flow. I'm wondering if this is just how the siphon gun works in this situation. I did this procedure to both the external cooler as well as the cooler in the radiator and had about equal flow through each. I'm not quite convinced this was enougth flow yet. Blowing air through everything with the air compressor produces quite a blast of air coming out of the exit lines.
The tranny guy told me a C6 should pump about 3/4 gallon per minute. So....I've been thinking....what type of electric pump can I attach to the tranmission lines to pump transmission fluid through everything and verify flow rate before I even get the transmission installed? Any ideas?

 

I don't know.. I mean fluids are viscous so fluid isn't going to (and isn't meant to) flow through a cooler with no resistance. I'm not sure I'd use cleaner for the coolers, anything corrosive could be detrimental to their performance. Just be careful what you use.

I think youre putting more prep into this than most. At this point i'd probably just put a return filter in it and feel ok with it.

 

hesteranger...i'm not overly concerned with the cleanliness of everything (althought that is important to clean things up after having a tranny let go). I'm more concerned why the transmission destroyed itself by lack of lubrication through the gear end of the tranny (rear portion). The output shaft got so hot it is blue, the gear cluster (planetaries) were all destroyed, and the aluminum housing of the transmission was ruined because a bushing spun inside the housing. Yea...serious **** here! I certainly don't want to put the tranny back in and potentially ruin another transmission. The transmission shop is confident the previous rebuilt was correct. I just want to make 110% certain that there is nothing wrong with the two coolers on the truck. I'd like to do more testing. BTW: brake / parts cleaner is not corrosive. Any ideas on how to go about that?

 

How often have you done tranny service?