AW-4 Auto Transmission direction of fluid flow

Hi All,

I have a 1992 XJ 4.0 Liter 4X4 with AW-4 auto trans. This vehicle has a transmission cooler. I would like to add a filter in the transmission cooler line. The filter has a preferred direction of flow. I need to know which way to install the filter.

AW-4 has two cooler line connections on passenger side. One connection is relatively close to the engine. The other connection is mostly towards the rear of the transmission.

Which of these connections does the ATF flow OUT of? The other connection will be the return.

Thanks!

My Service Manual shows this:

.

You better make sure the filter is capable of the flow/pressure of a automatic!

Don't quote me on this.
But I'm pretty sure that I have read that some of those diagrams are actually wrong.
So I Googled it and this is the first thing that popped up.

https://www.cherokeeforum.com/f2/pic-transmission-cooler-lines-diagram-chart-107766/

Now I recall reading this also. Disconnect a line and prove out the flow direction.

Regardless of the drawings, the front port is the output!

My '88 has the factory tow package that includes the aux cooler. It's hooked up exactly as the pic Tin_MN posted.

Out the forward port on the trans to the top port on the radiator. Out the bottom port to the aux cooler inlet. Out the aux cooler and back to the trans rear port.

My question for Mhead is why do you think you need a filter?

Hi All,

Thanks for replies! I see all agree that the line connected to the front (engine side) of the AW-4 transmission is the output for hot fluid and the rear port returns cooled fluid into the transmission. This connection is evident in the drawing.

I guess what is unclear is where the hot fluid connects to the radiator... top or bottom? I'll review my connections soon and post how my 1992 4.0L is connected.

I also have the additional transmission fluid cooler.

I'm installing a new remanufactured AW-4 and it seemed a good idea to install a filter. That said, the AW-4 I took out had 392K miles and was running strong. I just change the fluid every 30K. Maybe I'll skip the filter due to flow/pressure concerns by Saudad. I doubt I'll really need it and if the filter impedes the flow I won't know the transmission is overheating until it is too late.

If you are wondering why I replaced a good transmission, well, I figured it was just time. Better do it at my pleasure rather than have it pop somewhere. I like to drive far from home.

I really like the braded lines and I'm embarrassed to say I just use transmission rubber hose and hose clamps. Anyone know what pressure the trans cooler circuit runs at?

Thanks for advice and the cool diagram.

mhead said:

Anyone know what pressure the trans cooler circuit runs at?

Click to expand...

The test port figures from the FSM show almost 300psi.

RCP Phx said:

The test port figures from the FSM show almost 300psi.

Click to expand...

300 psi? I'd thought there'd be a lot more leaky hose clamp connections.

300 PSI? I'm shocked. I noticed a 300 PSI rating on the transmission hose I purchased but thought nothing of it. 300 PSI? Really? I can't imagine how my hose clamps haven't popped off and I've run them for a long time. How do the radiators hold this pressure?

I can understand 300 PSI within the transmission which makes sense for closing mechanical things or clutching but not outside the transmission.

300 PSI changes my whole attitude towards plumbing the trans cooler.

ChatGPT (my new friend) replies to question

How much pressure does the transmission cooler circuit have in a Jeep AW-4 automatic transmission?


The transmission cooler circuit in a Jeep AW-4 automatic transmission typically operates under pressure levels ranging from 10 to 30 psi (pounds per square inch). The exact pressure within the circuit can vary based on factors such as temperature, fluid flow, and load conditions. It's important to note that these values are approximate and can differ depending on specific vehicle configurations and modifications. For accurate and detailed information regarding your particular Jeep AW-4 transmission, it's best to refer to the manufacturer's documentation or consult a qualified technician.

Anyone out there corroborate 300 or 30 PSI as the pressure in the transmission cooler (radiator and additional heat exchanger) circuit?

The AW4 manual says: "(9) Press accelerator to wide open throttle position and note line pressure in Reverse. Pressure should be 223-to-273 psi <1540-to-1883 kPa>.
CAUTION: Do not maintain wide open throttle tor more than three or tour seconds at a time."

Obviously, ChatGPT never worked on an XJ.

I have never found a flow chart for a AW4, but most auto's have the cooler following the torque converter (that's where the most heat is generated) so even if it see's 1/2 of the pressure that's still over a 100psi!

mhead said:

How do the radiators hold this pressure?

Click to expand...

It doesn't have to, there is either a tubing or plate/fin core within the radiator.

Oil coolers should fill from the bottom, so they don't trap air. I doubt you'll see more than 50-psi on the coolers, since the discharge is straight into the pan.

If you add a filter, make sure it has a pressure bypass.

The numbers I posted earlier are the max pressures. In Reverse, parking brake on, wheels blocked, wide open throttle.

The numbers at idle are significantly lower.

(6) Shift transmission into D range and note line pressure with engine at curb idle speed. Pressure should be 53-to-61 psi (363-to-422 kPa).

(8) Shift transmission into Reverse and note line pressure with engine at curb idle speed. Pressure should be 73-to-87 psi (500-to-598 kPa).

However, also bear in mind these are at the test port, not the outlet. I could not find any mention of pressure testing at the outlet itself. The outlet itself only needs enough pressure to push the fluid through the cooling circuit.

lawsoncl said:

Oil coolers should fill from the bottom, so they don't trap air. I doubt you'll see more than 50-psi on the coolers, since the discharge is straight into the pan.

Click to expand...

Excellent point. In this regard, the only pressure will be due to the fluid viscosity relative to the passage dimensions.

lawsoncl said:

Oil coolers should fill from the bottom, so they don't trap air. I doubt you'll see more than 50-psi on the coolers, since the discharge is straight into the pan.

Click to expand...

This I've been unable to confirm, maybe will try next time I have the pan off!!!

I agree, pressures are those expected at the pressure test port and not necessary the pressures in the cooling circuit.

The pressures mentioned can be seen in the operator's manual page 7,8 which gives the pressure measurement location as "test port". Link to manual is shown below.

"discharge straight into the pan" is an excellent clue. The interior of the transmission runs at atmospheric pressure due to the vent at transmission top. So the pan pressure is atmospheric and at least the pressure at the return point is known.

Unless someone has a more certain cooling circuit pressure, I'm going to keep to my transmission line hose and hose clamp rig.

Thanks for replies!

https://cdn.xjjeeps.com/pdf/en-us/aw4-transmission-service-information.pdf