C4 towing overheating...Cooler flow tests?

I am towing with a 91 mustang 302 EFI HO in a 4x4 Bronco II with a C4 behind it. I can hold almost any hill at 60MPH @ 3500 RPM in second gear with a ~5000 pound camper trailer. The problem is transmission temps.

I have a HUGE tranny cooler (covers half the rad) and I still can't keep the temps under control. I am measuring in the pan and the first good hill puts it at 220 deg, and after that I still does not cool on the flat actually goes up slowly still.

I just came back from a short camping trip (20 miles out) and I had 225 deg temps coming into the driveway with only one big hill.

I have to go on a 300 mile trip in a week and I need to get better control of this. I don't mind seeing 225 at the top of a hill, but running 60MPH on the flat with the gauge still slowly creeping up has me worried.

The transmission shifts very well with a Transgo stage 2 and a couple extra clutch's. The converter is a stock C5 unit from a 81 C5. Trans case is a heavy duty pan fill with a shimmed bellhousing for the C5 converter depth. There is no case mods for cooler flow.

I am open to any suggestions.

I would really like to do a cooler flow test, but I need a spec for cooler flow volume.

I am unsure about cooler flow volume but I know that at normal idle you have between 15 and 25 psi pumping out. I read these #'s on a tranny flush machine which uses the tranny to flush it's self.

Having a large cooler in front of the radiator is nice but do you have a good flow going through it and are the fin's large enough to dissapate heat readily?

Also, think about welding some fin's on your pan if there aren't any clearance issues, maybe that will help you a bit at cruising speeds....


FE

That is hot.
I am thinking that the converter might be the culprit.

I am interested in what Paul and Gregg have to say.

Is it possible to put a fan on your tranny cooler?

I think you need to disassociate your tranny cooler from your Radiator and give it it's own fan.. Similar to this pic of the Battlestar below.

The tranny cooler is about 2-3 inches in front of the rad, it is the first thing to see the air coming into the engine compartment. Fans are great for cooling a drag car in staging or the pits, but running down the highway at 60 MPH is air movement that a fan can't match. I don't think a fan will help me out.

I don't think the airflow is the issue. I do question the old C5 converter, but its stall speed is so low (1400 RPM with this motor) that I don't think it is slipping too much.

It's possible that the tolerances in the tranny are too tight an there's too much friction, isn't it?

Is it possible the flow is going too fast through the cooler and not cooling properly, and maybe you need a flow restrictor?

A restrictor would increase pressure and decrease flow. Not going to help.

Internal thrust clearance was fine when I had it apart last. I had it shimmed tight (.015) as C4's like that, but I could still turn the input by hand. Knowing C4's it has more clearance than that now.

Ok ,normal cooler pressure will be in the 30-50 psi range. As for flow amount i've not seen any figures published but you could check with the return line disconnected to make sure the cooler circuit is free .Just start at idle and into a clean container to see how much pumps through.
If you have good flow there rules out any probs in the pump area and that the checkball is free and that the cooler itself is not restricted.
Next i would be checking the case at the return, remove the fitting and check the passage in the case is free of any restrictions.
One C4 i got to rebuild had burnt oil and that passage was blocked. Check maybe with a piece of wire or a drill bit maybe to see it is clear. All the cooler in the world wont work if the oil can't return.
There is NO kinks in any of the cooler lines ?

I have been doing a lot of testing with temps last few weeks on one of my C4's in a friends car. Is one of my C4's using a stacked plate cooler from PWR (PWO1223- 280x255x19mm)with -6 lines. Has the usual pump mod and deep pan etc and full manual valve body runs up to 210psi with a high stall 9" converter. With a temp gauge in the pan it is hard to get it warm. After a 10 second pass trans temp is showing just on 160*F .

If your cooler line are free and you have flow. I still say converter might be your heat source.
You are towing maybe 2 times the weight the C5's normally see.
I also would not run the cooler lines thru the radiator.
Ever calc the converter slippage?

Flow as far as VOLUME, at 20 psi the trans cooler lines (at idle) that are 3/8" diameter will pass 15 quarts in about 7 minutes.

You can approximate flow at diffrent PSI with diffrent Mathematical calculations to tell you the answers.

If KINGOFAZLE were here he'd have them on the top of his head, he's a damn mathematical genius

But since I've flushed trannies at idle under 20psi at 15 qts per 7 or 8 minutes, you can for sure find out the flow of your cooling lines with the pressure running at say 50 psi...