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BW66 Check-up and ATF Flush (BW66 & 12)

BW66 Check-up and AT Flush (BW65, 66 & 12)

Kyle Chatman, Stefan Knappe and Per Stanius

Since this topic came up on Jag-lovers recently, I thought that I would repost a message from about a year ago. I do wonder if part of the BW transmission's bad reputation isn't due to incomplete maintenance, and I recommend that you flush the system when you change the filter. Why? By my calculations, if you change the transmission oil every 30K miles, following your change at 90K miles your transmission will contain about 2 quarts with 90K miles, 1 quart with 60K miles, nearly 2 quarts with 30K miles and about 3 new quarts. That's an average of 45K miles and you're about to use this mixture for another 30K miles. That's why I recommend a flush and a flush is very easy on an XJ6. Also, this was my second favorite project on the XJ6 -- very rewarding.

But first, try the following test to check-out the 66.

  1. I'm not an expert, I'm barely a novice, but I thought that the following two tests should give you some comfort if you are generally satisfied with the transmission's behavior and it doesn't whine in 2nd gear. (My source is a Mitchell publication on transmission available at our public library [beginning on page 6-17].) Under full throttle, the shift from 1 to 2 should be at 41-51 MPH and the shift from 2 to 3 should occur at 73-81 MPH. That is the fun test and I recommend that you keep your repair manual open on the passenger side in case you're stopped by the law. The second test I tried was a stall test. I had never done this before so it seemed rather strange, but the idea is to pit the engine against the brakes and see what RPM you can reach. Engage the emergency brake and push with your left foot on the brake pedal. Shift to Drive and step on the gas with your right foot and monitor the tach. Make note of maximum RPM reached. Don't try this for more than 10 seconds at a time. You should reach 1950-2100 RPM. If your stall speed is higher, then clutch or band slippage is indicated. I recommend that you do this before changing the ATF and it probably would be a good test for a used car purchase.
  2. Replace ATF filter and add about 4 quarts (this will overfill the pan in preparation for the flush).
  3. Flush the system. I recommend a two person team. My 13 year old son was the top-side member. I was under the car where I disconnected the rubber hose at the water cooler tube connection. Disconnect on the exhaust-manifold side of the car. (If you disconnect on the intake side the fluid will spray out of the tube hole and make a mess.) The disconnected exhaust-side rubber hose can then be directed into a plastic gallon container. My son started the car and the transmission pumped out fluid in a hurry -- transmission is left in Park. At two quarts, my son turned the car off and we added two quarts of new fluid. We continued to do this for about 8 quarts worth: pump out two, add two, etc. The last two were Redline synthetic. It was very easy and requires only a plain screw driver for the clamp and pliers to work the hose loose. You might try this if you want to change fluid more frequently than you change AFT filters. I think that 3 quarts is about the maximum that can be removed in one cycle using this method and it might be possible to keep up with the output but my partner didn't feel comfortable trying.
  4. Add fluid to bring to proper cold level as directed in the owners manual. I recommend that you follow-up with a hot level test when the after a 20 mile drive (when you get a chance).

Per Stenius has since informed me that some models may be different. While helping a friend with a Series II ATF flush, he discovered that the opposite connection had to be removed. He was not certain whether it was a switch of hoses at some point or an original difference. I suppose the best advice is to be prepared to stop the engine immediately if the flow is a different direction.


Stefan Knappe

I would add one little thing I found during the process. After you have taken off the transmission oil pan and removed the filter, a separate distance block falls into your hands also. This distance block is mounted between the valve block and the filter. On both sides thin paper gaskets are placed, which did not come with the new intake filter. If I would have known of their existence, I would have bought them in advance to renew them. I had to reuse the old ones, which was no problem.

BTW, I asked a well known Jaguar/Rolls-Royce specialist in my area (who frequently rebuilds these transmissions himself) about which fluid I should use. He strongly recommended to stay with the original fluid. He was the only place having it in stock, and I bought ten liters at DM 18,60 each. Rather expensive. He had it in a big container signed 'CASTROL TQ-D' where it was pumped out. Now I have (at least) the feeling of having done the best to keep my transmission (141.000 km / 90.000 mls) in good order.


Per Stanius

I did that oil change/flush on the BW12, and here are some comments:


  1. Oil comes out from the hose on the intake side when flushing
  2. Removing oilpan somewhat of a hassle due to close proximity to exhaust pipe. Need a flexible extension to reach one of the bolts.
  3. Oil pan bolt torque spec is much higher than S2/3: 10-13lb/ft (S2 is 5-6...)
  4. Gasket is cork (does this go on wet or dry??? I put some grease on mine)
  5. Oil filter is simple wiremesh, no gasket there. I think these can be cleaned instead of actually replacing them. I kept mine, since it looked so good.

Using the correct (Type F) fluid makes shifting MUCH better - Dexron is not good for the bw12.

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