Tansmission Temperature thoughts ---

[civdiv99]

Great comments.

I get that there is no revelation here that somehow something is wrong with the stock X5 design. I don't think for a minute there is. I also know that manufacturers shoot to hit 212 degrees if possible to boil off moisture. BUT, I'm not running the OEM fluid, and I know many here who may have changed aren't either, so my point is anyone can do a quick search of transmission temps vs service life. There's a gazillion charts out there - and my Allison manual came with it's own - and it don't like getting much over 200, high $ synthetic and all. I'll stick with the cooler running temps and see how it goes. And I'll follow up on this every now and then - including a failure. Until then - I personally prefer a lower temp.

Some observations I've made just on my vehicles -

2011 Camaro SS 6-sp auto the trans temp runs 180~190 but will climb with spirited driving (which means all the time if I'm driving)

Class A motorhome w/ 8.1 and 5-sp Allison runs maybe 160 going down the road but will hit 190 on a long summer climb. Pulling a car.

2005 Toyota Tundra - only temp I've had is hitting the pan with an IR thermometer. Was running maybe 160 that day, but was a one time check. It has a stand alone trans cooler from the factory as part of towing package.

[JCL]

Originally Posted by Ghost-Flame

Is there an advantage to having an auxiliary trans cooler on these transmissions even towing a trailer or a boat?

I tow a trailer with my Motorcycle with my 3.0 e53. The trailer and Bike weighs about 1200 lbs. I generally do high way trips but, I go as fast as I can... 70 to 85... 90 depending on the State. I always wonder if I am abusing the trans and have thought about getting a trans cooler. Based on these 2 above posts It sounds like the transmission has plenty of cooling ability and cooling it further may be detrimental, am I correct?

Well, this is just my opinion, because I don't have hard data to back it up. That said, my observations jibe with it. I don't think you are doing any damage to your transmission at those loads. And speed doesn't equate to transmission load. Steady state on the highway, if the torque converter is in lock up mode, isn't putting any significant heat into the transmission.

Originally Posted by Ghost-Flame

Are modern transmissions better at cooling than the old automatics? My uncle burned up a transmission on a brand new 1970ish, loaded, ford LTD station wagon, pulling a pop up camper, when they replaced the transmission they put an auxiliary cooler on it and it lasted for years after that.

Yes, much better. I used to install transmission coolers on vehicles like that (we even had a succession of LTD wagons at home, up to the 460 cid, and used for towing). If those vehicles were towing much, we also put in shift kits, usually a different check valve and spring in one of the passages in the valve body, to firm up the shifts and reduce clutch slippage.

Older automatic transmissions were great sources of heat, and consequently burnt the transmission fluid fairly easily. That is where the whole fluid change process that is debated here came from. Modern transmissions convert more of your engine power to forward motion, in a quest for fuel economy, so there is much less waste heat generated. Less heat means the transmission fluid lasts much longer. Part of it is the transmission shift strategy (backing off the timing during a shift using the ECU, to reduce power and reduce clutch slippage) You can tell that one works, since clutch plates come out of high mileage BMW transmissions looking like new (as reported many times on the rebuild posts) and old 1970 era clutch plates came out cooked. An even more important element is the lock up torque converter. A slipping torque converter generates heat, and all older ones thus generated a lot of heat. A locked up converter (and BMW uses an aggressive lock-up strategy) doesn't produce any heat, as there is no relative motion to churn the fluid.

As a side note, that is what is most important when you are pulling a trailer, that you keep the transmission in lock-up. You can tell when it locks or not (revs change) and as long as it is locked up you are being very easy on your transmission, no matter what load or speed you are at. Too much load and you will have to drop a gear to keep it locked up, but that is better than trying to pull a higher gear and generating heat.

Jeff