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SHO RadiatorTransmission Cooler - How To Clean

new 10/26/2007

Larry—Background—I started this in tracking down an OD off warning light last July. Ford had installed an external transmission filter in the air to oil cooler outlet line with the new tranny at 95K (200K now). When I got the OD light, I had no performance related symptoms to cause an overheat condition and so I checked the oil flow thru the cooler system. Since I bought this car in May 99, I have changed fluid about once/ year, by pumping out thru that same cooler line and I knew immediately the flow was restricted (about 0.2L)- it should be approximately 1L/min. I also checked flow before and after that filter and the filter wasn’t clogged. I then checked flow going into the cooler and found normal flow. I used compressed air to blow backwards thru both coolers and about a teaspoon of non-metallic debris came out—I reassembled and rechecked flow, changed fluid and everything was back to normal and no more OD off lights. ( I had also isolated the finned heat cooler and tested it but no clogging there and in retrospect the radiator cooler protects it and if that large tube becomes clogged you have other serious transmission problems). I checked things again about 5000 miles later and flow was about 60% of normal. I repeated the above, but then removed the external filter from the outlet/return line and installed a new one in the inlet side to protect the cooler. The filter is Ford PN XC3Z-7B155-BA and it is easily installed in the 3/8” rubber line on the air to oil cooler outlet. This filter also has a bypass/ relief valve. I also considered bypassing the radiator cooler and adding an auxiliary cooler but did not want to deal with cold weather issues in this my daily driver.

The procedure follows below:
Procedure to clean SHO radiator transmission cooler(s) (based on 99 model year)

This procedure assumes you have determined you have a low transmission oil flow condition but can also be used to check for correct oil flow. Other things can cause this condition, but one of the easiest (and cheapest) to check is a restriction or clogging of the oil cooler in the radiator tank. This condition gave me the OD off light.

The SHO transaxle fluid is cooled first by an oil/ coolant heat exchanger in the radiator tank in series with an oil/air finned heat exchanger in front of the lower radiator. The transmission cooler is the upper finned tube—the lower finned tube is the power steering fluid cooler. Transaxle fluid flows from the transmission to the bottom of the radiator cooler, out the top of the radiator cooler and into the air to oil cooler on the right side of the car. The oil to air cooler outlet is on the left side and from there it goes back into the transmission. The oil lines consist of combinations of steel tubing and rubber hose using hose clamps and spring lock connectors. This procedure can be conducted without opening any springlock connections.

The inlet to the oil/radiator cooler is easily accessed through a hose to steel tubing connection (hose clamp) located on the left side of the lower radiator shroud. The outlet is accessed by removing the hose/ hose clamp on the left side of the upper finned tube. Once the system is opened, you need to make temporary connections with scrap hose/tubing etc to direct oil into suitable containers and to adapt your air hose to the finned tube outlet. Once you have made the necessary connections, blow air in the outlet/ reverse direction of the oil flow. I would not make a hard connection with an air gun or air hose to avoid over pressurizing any of the components—I think the coil in the radiator tank narrows down in the bends and any debris should easily come back out. Once you have cleaned the tank cooler reconnect the inlet line, direct the oil outlet into a suitable container, and check oil flow by starting the engine and measuring flow—normal flow is approx 1L/min. Reconnect all lines, top off fluid and check for leaks.

I have also installed a filter in the inlet line to protect the cooler. It is Ford PNXC3Z-7B155-BA and goes easily in the inlet hose at the lower left side of the radiator shroud. This filter has a bypass/ relief valve.

Larry – with all the usual disclaimers
Harry Skruch
Baltimore MD
99 BLK



Harry is a recent addition to the family, and already he's in the thick of things. Thanks Harry.

He even used his smell chekker!! Great form sir!!


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