A604 Cooler Flow & Repeat Planet Failures


    Planetary failures are a pretty common sight in transmission shops all across the country. The Chrysler A604 units are common to planetary failures. It’s no big surprise when the teardown man tells you upon tearing one these units down to find complete planet meltdown. The problem is when You replace all the planetary gears with New / Rebuilt ones and it comes back on the tow truck .

    You go check it out, run codes etc. It has to come back out of the vehicle. Upon teardown the builder finds little tiny pieces of black, crunchy (non metal) pieces in the pan of the unit and complete planetary wipeout. The little pieces in the pan almost look like someone got floor dry into your unit. The R & R man swears he let it flush for almost a hour before he installed the unit and the gauge on your new lines flusher showed everything was normal.  The builder now suspects either the customer drives with a lead foot or You got a bad batch of parts because you have done hundreds of these things and you know it was all setup perfect when it left your bench. What happened ?

    Does this story sound so familiar ? We are going to try & explain a few things. The main cause & # 1 sign of a radiator problem is that little black crunchy material found in the bottom of the pan as seen in the picture below.

# 1 Cause

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   The Transmission oil cooler tank (as seen below) has water/antifreeze flowing all around it and down thru the middle of it to lower the ATF temperature before returning it back to the transmission as lube oil, draining back into the pan and starting the cycle all over again. The stock oil cooler (as seen below) is hollow inside, allowing coolant to flow thru the middle of it. This leaves a very small area for the ATF fluid. ATF upon entering into the cooler must weave up and down to make it’s way thru the brass mesh contained inside.

Inlet & Outlet

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    ATF upon entering into the cooler must weave up and down to make it’s way thru the brass mesh that’s not more than  .125 thick. This brass weaving has very small openings for the ATF to make it’s way thru.

Cut Cooler Tank

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    The debris is collected down in the end of the tank near the outlet. Thus, restricting our lube oil that’s returning back to our transmission. On our test vehicle, the longer that the vehicle was run , the more the cooler flow dropped. When compressed air was blown thru the lines everything seemed OK. Here is the results of the flow tests.

Collected Debris in Cooler Tank

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Cooler Tank

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* Note—Guage readings were taken on the radiator return line to the transmission*


Vehicle Cold at 1000 rpm’s in Park

.4 GPM (Gallons Per Minute)

30 psi (Pounds Per Square Inch)


*After 15 minutes of running time*

Vehicle at 1000 rpm’s in Park

.1 GPM

8 to 10 PSI


That’s Less than after 15 min’s running !


* New Radiator Results*


Vehicle Cold at 1000 rpm’s in Park

.7 GPM

40 PSI


When Tested in Overdrive with wheels off the ground

1000 to 1500 RPM’s

1.0  GPM

55 PSI


    Now, to answer the question on how did we come up with these readings. We built our own flow tester. As seen in the photo below.

Flow Meter

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     The radiator in this 1992 Dynasty gave us another surprise. We had done removed the tank off of the radiator & it was leaned up on a teardown bench so that any drainage would not make a mess. The radiator fell down flat onto the bench, when we picked it up to our surprise, the radiator was FULL of debris from when it spent time in the body shop for some frontend repair. This car was well taken care of and kept clean. With this car having air conditioning, You couldn’t see how bad it was plugged up.


 Debris Plugged Radiator

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OEM Cooler bypass Valve plugged with debris

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