Trans fluid flow path
 

Can someone confirm for me that the trans fluid flows into the radiator cooler through the passenger's side fitting and out of the driver's side fitting?
Thanks in advance for the help on this.
-Bill

Re: Trans fluid flow path
 

Hi Bill,

There's a few threads on this somewhere. I had asked the question myself, but now I've forgotten the answer. :-(

I have a diagram in my locker.You will find it HERE

Okay, if I read the diagram correctly, the fluid does flow into the radiator through the passenger's side fitting and out the driver's side fitting.
Thanks!
-Bill

In the parts diagram it lists part 5 (going into the passenger side of the radiator) as the HOSE ATF IN hose and part 6 (driver's side of the radiator) as the HOSE ATF OUT.

When referring to these hoses as "IN" or "OUT", are they referring to the radiator or the transmission?

http://www.subaruparts.com/diag/?mod...category=450-B

attached is a drawing showing fluid flow from the OEM add-on filter going into the pass side (US versions anyway) and out on the left.

this is from the tech bulletin I got from alldata.

Oh wow I really disagree with that flow path. Which way is the flow in the bottom header of the radiator? It is from the passenger side to the driver side. The oulet form the radiator is on the driver side.

There are two ways to connect a fluid to fluid heat exchanger, parallel flow or counter flow. In parallel flow the hot fluid and cooler fluid move in the same direction and in counter flow they move, well in opposite directions.

In parallel or counter flow, the cooler fliud, the fluid doing the cooling gets hotter as the heat is removed from the hot fluid.

In the parallel flow case the temperature differential between the hot and cool fluid is less because the cooling flow is heated up raising lowest temperature available for cooling.

In counter flow the maximum temperature differential is obtained and the maximum heat transfer rates are obtained as well as the lowest possible outlet temperature for the hot fluid.

The diagrams links above show AFT entering the passenger side. The AFT gives up heat to the coolant. The coolant gets hotter and is still flowing over the AFT heat exchanger in the same direction as the AFT flow. Now there is hotter coolant to cool the AFT. This is parrallel flow.

Reverse the AFT flow so it enters the the driver side. The AFT give up heat to the coolant and the coolant moves off of and away from the AFT heat exchanger. This is counter flow.

With the extra AFT heat exchanger installed in front of the a/c condensor, driver side, half, connected in series after the Raditor cooler, the lowest possible AFT temperature can be obtained.

Heat from the aux AFT cooler will raise the raditor coolant temperature becasue the air passing thru is hotter from the aux trans cooler.

Well any way, that is how I got mine set-up. And this really only matters when one is drving the SVX HARD. :D

Okay, here's what I'm seeing so far (yep, glad I asked this question:D )


If we accept that since the aux filter diagram that Lee provided is consistent the figure that Nubs provided that the flow path is as they indicate then -

Hose 5 is on the Driver's side and ATF In means into the transmission
Hose 6 is on the Passenger's side and ATF Out means out of the transmission

I agree with SVX Commuter that this means we have parallel flow wrt heat transfer, as the radiator coolant flows out of the hose at the bottom of the driver's side of the radiator.

Since there is a pump within the trans that circulates the fluid we are now faced with the fact that either we have the flow path backwards or Subaru made an engineering decision (maybe they were more concerned with warming the trans fluid up?) to go with parallel flow.

My bottom line concern here is that the PermaCool filter I've got does have designated In/Out flow path that supports the filter's "relief" feature (allows for flow even when the filter gets clogged up). Hook it up backwards and, according to the instructions that came with it, you don't get the by-pass when the filter clogs up.

Has anyone actually gotten under their car and seen which line gets hot first?

-Bill

I love this site. Always new things to think about.

but first, just to confirm, the OEM flow is from the transmission to the OEM add-on filter, then "in" on the right (US version passenger side) side of the radiator and "out" on the left, then finally back to the transmission pan.

I had never thought about parallel vice counter flow. Is there a reference that describes the dynamics? Seems in counter flow that the end state of the fluid being cooled (which one ATF/Water is suspect here too) is opposite to the hotter end of the cooling fluid. I would suspect a significant temperature differential might be necessary to observe a strong correlation.

In a practical sense anybody have knowledge (or feel strongly) what the temperature differential is from one side to the other?

Lee,
My guess is that the trans fluid is always hotter than the coolant in the radiator - except when it isn't, and then I think Subaru figured they wanted the coolant to actually bring the trans fluid up to temp so the converter will lock. I've got to figure they did some conductive/convective heat transfer analysis before they decided on the design they implemented.
-Bill
p.s. yeah, this site is the best!

Hi Bill,

I'm sure the intent of Subaru in placing the ATF cooler inside the radiator was to control the ATF temperature. However, I don't think they properly accounted for city driving in 100F temperatures, and they knew it. Have you ever read the warning label about the ATF temp on the sunvisor? Its quite humorous. Subaru basically says that if the ATF overtemp glows, then you should refrain from hard driving until the light goes off. I LOL'ed when I read that. They are basically admitting that they did not account for all possible driving conditions in designing the cooling system for the ATF. And they never bothered to fix it! That's what kills me.

They should have also added to that - if your light goes on, you just toasted you ATF Fluid and you had better change it ASAP! :)

This is directly from the SVX service manual on the cooling section diagram:

The ATF cooler INLET hose B (#18) is going INTO the DRIVER'S side of the radiator.

The ATF cooler OUTLET hose B (#19) is coming OUT of the PASSENGER side of the radiator

another way to look at this...
 

The ATF line out of the tranny is at the bottom of the tranny, right? Trace that line to the radiator and that is the ATF line into the radiator.

Well I have not looked at the service manual's but when I installed my cooler I also flushed the tranny. I pulled the hoses off of the hard lines to check the flow path and the way I showed was the way I hooked up my filter and cooler. It has been that way for almost three years know.