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      11-09-2012, 12:20 AM   #1
N54_Fan
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Drives: BMW
Join Date: May 2008
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FIRST (well 2nd really...) AUTOMATIC TRANSMISSION COOLER for E9x (pics & Diagrams)

So for quite some time I have been determined to get my car road track worthy. Many of you may know I have spent a lot on "reliability mods" since AT 335i tend to have overheating problems at the HPDE track. About 7 weeks ago (after tons of research) I had personally custom designed an AT cooler. There is not one currently available for purchase and this has never been done before (Actually, ...AR design did the 1st and only other one but never marketed it) So, I met with the Frank Benevento at PSI Tuning (Precision Sports Industries) in Winter Park, FL. (407) 617-0372 to have them do the work. 2 days after that my car was hit by a lady in a motorcyle while I was stopped at a light. She hit me so hard my bumper, fog light and driver side oil cooler were crushed. I had plans for HPDE at Sebring exactly 3 weeks after that accident. My car was in the shop for the next 3 weeks. I almost did not make it to Sebring but Frank at PSI really pulled through for me and got my AT cooler and all mechanical work done in time. The delay was in the design of the cooler and how to mount the cooler. Frank spent HOURS getting it right. I must say he really did a great job and spent much more time than I expected to make sure the job was done right!!! AWESOME Customer service by Frank...I highly recommend him for any work on your E9x.

Part of the issue is the appropriate size cooler. I had chosen the largest transmission cooler that I thought would fit. I initially chose the B&M 70274 Supercooler because this is what most Corvette guys were running and most people say its nearly impossible to over cool your tranny fluid. (Most data also says the transmission fluid lifespan decreases by 50% every 6 degrees F over 200 F. Some say the ideal ATF temp is about 180-200 F.) This cooler will NOT FIT in front of the radiator. It could possibly fit if placed in a wheel well but I did not have that option given my Dual ER Oil coolers. The reason it would not fit was because there is a power steering cooler that is about 18" x 2.5" x 1/2" that is just above the intercooler (See pic 1 & 4) and hidden by the front bumper and plastic shroud that diverts air to the radiator area (I really never knew there was a PS Cooler on our cars). In the end we had to go with the slightly smaller B&M 70272. Next problem was how to mount it. The cooler should NOT touch the radiator as this would transfer heat to the radiator and diminish the radiator's cooling ability. There should be a gap of about 1/4-1/2" between the 2. Also the cooler should NOT block air flow to my Cyba ducts for the DCI. The guys at PSI made a custom mount for this. We had to cut a portion of the rubbery plastic shroud that diverts air to the radiator area. See pics 1 & 4 below. The cooler is mounted as low as possible to allow the hoses to come off from the top of the cooler. Hoses should always mount to the top or come from the side to the cooler and never from below. Running hoses from below increases the risk of air pockets and poor cooling. We chose to mount the hoses to run behind the Cyba scoops. See pics.

I chose to use a T-stat to allow the tranny fluid to warm on cold starts and only divert flow to the new cooler when above 180 F. I chose an Earl's 501 ERL 180 F T-stat. See pic 2. I also chose to mount the T-stat AFTER the heat exchanger. The BMW E9x M3 has this same setup with the same heat exchanger as our cars. In fact they use the same part number as our factory oil cooler for their tranny cooler. The only difference is that the M3 plumbs the transmission cooler in parallel and I designed this in series for ease and because that is what most have done on Corvettes and other big V8s with good success. In addition there is really good data to prove that in series is more efficient than in parallel. I chose -6 AN nylon braided hoses and black anodized AN fittings because I wanted less weight that SS lines and my ER dual oil coolers had nylon hoses... so for continuity of looks as well. I left the fittings to Frank to decide since he would have to figure out which ones he needed. Frank @ PSI custom made a mounting bracket for the T-stat and this mounted perfectly to the chassis behind the waterpump. See 2nd & 3rd pic. The heat exchanger's top hose (#2) in the diagram below (See pic #6) is the outlet from the heat exchanger and return line to the transmission. This line was intercepted to T-stat and the inlet to the cooler. The cooler return line goes back to the heat exchanger return line back to transmission. (See pic in pdf file)

So how good does it work? So far I have limited data and probably will be unable to get really good temps until early next week (was hoping this weekend but does not look promising). I have a temp sensor mounted to the Earl's T-stat for the inlet hose and outlet hose. The inlet hose will give me an idea of how efficient the factory heat exchanger is since one temp sensor is mounted after the exchanger and before the cooler. If the heat exchanger is efficient enough then the AT cooler should barely come into use as the T-stat will close when temps go below 180F. The reason for limited data is I picked up the car at 9:00pm Friday and drove directly to Sebring for the Sat/Sun HPDE. I had no time to hook up the temp sensors to the PLX gauge I have. So on my way to Sebring that night I pulled over and measured the inlet and outlet hoses temp with an IR temp sensor. They were 176 F inlet and 154 F outlet after 1 hour of normal highway driving. I am sure the fluid temp inside the hoses are higher. The next day at Sebring I expected to get some time to install the temp sensors but my car developed an electrical problem. Long story short,...it seems the accident caused a loose connection and an electrical short. The car went crazy and the car was now at the dealer for nearly 3 more weeks to fix this electrical problem. Thankfully it was an easy fix albeit time consuming to diagnose. So, I got my car back yesterday and everything seems fine. I will plan on hooking up the temp sensors as soon as I can but it looks like it will be early next week before I can compare these to water temps and give more detail.
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File Type: pdf bm_cooler_techdoc.pdf (590.3 KB, 141 views)
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