Cooler line Pressures

[WVtrucker]

What kind of pressure is on the trans cooler lines for a stock 4R70W? thanks!!

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[Bluegrass]

There is no really hard answer to the question except to say that if measured you would not find very much.
Reason is the outlet from the front pump goes to a line then to the radiator cooler then either through an aux cooler or back to an open pan.
The resistance to fluid flow presented to the fluid by all parts of this loop is the only means for pressure to build to any level.
Same as opening a hose to water from a facet. If the hose is open on it's end, there is no pressure but only volume flow out the end. Put a spray end on to back up the water, reduces the flow and raises the pressure, then it's a different story. Same with the trans cooler lines.
You would never want to impede the fluid flow any more than is nessesary to accomplish the total job of cooling the fluid returning back to the pan and still keep near total volume flow.

Sorry if I over done the answer.

[WVtrucker]

Thanks Bluegrass. That is more or less the answer I was looking for. Since there is little to know restriction to the flow given the pump output volume there is very little pressure.

Thanks again.

[casey_1]

Actually the return from the cooler goes to lube the trans, not to an open pan. There is an orifice in the lube circuit so there is pressure in the cooler lines.

I've seen up to 60 PSI in the line to the cooler. There is also restriction in the cooler, the return line is quite a bit lower, usually below 20 PSI.

[Bluegrass]

Casey, are you sure about the restrictions?
I have never run onto this before anywhere.
Where can this be documented?
I have an ongoing interest in fluid cooling the trans and have a specific setup that does not include the radiator cooler in the loop, for summer time towing.
Testing has shown that the fluid temps out of the last cooler are lower than the pan temp.
I can easily put in a pressure gauge as part of the learning curve, to varify how much there is in my setup. I would expect there to be some.
Sometimes there is restriction used in certain designs the slow the fluid if the design allows the flow rates to be so high that fluid cooling is less efficient becasue it passes thru too fast, then there may be pump requirenents also.
With two coolers in series i'm sure ive added some restriction as well as more cooling area but works good so far.
Then there is a matter of wintertime fluid cooling.
With my towing setup, I expect it to be too much cooling for cold weather so will hook the radiator back into the system this fall.
The trans has a temp sensor that won't allow OD until it come up to sensor temp besides a bit of stif shifting until that point.
There seems not to be any large amount of info on all these areas, 'commonly' available.
Thanks.

[casey_1]

Originally Posted by Bluegrass

Casey, are you sure about the restrictions?

Yes.

Originally Posted by Bluegrass

I have never run onto this before anywhere.

I have. Every trans I've been inside of uses the return fluid for lube. There are restrictions in the lube circuits bacause the fluid has to flow through some small passages.

Originally Posted by Bluegrass

Where can this be documented?

In the shop manuals. And I don't means Haynes or Chiltons, those are not shop manuals. They are general overviews for those that don't want to know a lot, or spend a lot of $$$.

Originally Posted by Bluegrass

Testing has shown that the fluid temps out of the last cooler are lower than the pan temp.

That is because the return fluid goes through the lube circuit where it picks up some heat. If the cooler just dumped into the pan, the pan temps would be just about the same as the cooler return.

[Bluegrass]

Thank you. Thats something I was not awhere, of never being inside one except to change fluid and filter.

[WVtrucker]

That's why I love this site. I learn something new almost every day