Tansmission Temperature thoughts ---

[civdiv99]

Some of you may recall maybe 1 1/2 years ago I did a garage rebuild of my 5HP24. I used a Mobile "multivehicle" synthetic trans fluid. It's been fine.

Now, I also run a B&M trans cooler up front - it fits nicely between the electric fan and the radiator. More thoughts on why I do this follow.......

I posted some info maybe a month ago on reading the trans temp with a multimeter. Of course a IR gun will give ya close enough - I have additional plans for the process I outlined so tossed it on the board while I was at it. But I'd be curious to know if a few of you could hit your pan with an IR therm and let us know what your trans pan temp is after driving around on what counts as a 'warm' day.

It just drives me nuts that BMW will run the trans as hot as they do. I'd bet way over 200 degrees fluid temp. They do this to accomodate the "lifetime" fill idea as the oil needs to exceed boiling point of water to boil off moisture that may condense inside since it's not getting changed. (The trans vent tube is tucked way up in the tunnel).

Since I am not running the lifetime secret squirrel sauce, I am going to have to change it regularly anyway (not that I'd consider the other stuff lifetime in terms other than the "transmission's" lifetime).

The 5HP24 first use was in what - 1995 (ish)? So was under development to whatever extent before then. Way before the secret squirrel sauce and lifetime fill mantra. Now here's where I am going with all this rambling. The ZF kit for my 2002 covered the whole range of years and applications. In other words, the o-rings and seals and various other part numbers didn't change over time and aren't unique to BMW applications. They are the same parts as when 30K changes were commonplace. While I suspect this high $$ fluid is more tolerant of operating temps that seem contrary to good trans oil life, I'm not convinced it's necessarily the best plan. Best compromise to sell cars with a minimum of req'd dealer svc maybe -

Anyway - I would really like anyone using stock trans setup to give us some readings off the pan after driving around or highway trip - I want to know what you see.

And second point, granted I'm a tinkerer, but for those of you (like me) who have strayed from the lifetime fill koolaide, you might want to consider not just the fluid properties in terms of compatibility, but realize that even quality trans fluids generally have a problem with high temps - and trans fluid life drops precipitously when you get well into the 200s. I'm running in the 150s right now, but it is not hot (or warm) out.

Hell, I have a class A motorhome running an Allison with their synthetic transsynd fluid ($$!!!!) The Allison folks included a chart reflecting shortened trans life and effects of temp. That thing only runs trans temp of maybe 170 across Nevada in August (I have a digital readout).

[faranks]

After doing my rebuild and trying to fill correctly, my pan never got that hot according to the IR gun. I still have to top off, so I will take a spirited drive and take an immediate reading.

[civdiv99]

Thanks. Stock trans cooler uses engine coolant to help get up to temp, but it's still just the little box down there catching whatever wind comes off the fan. X5 4.4 runs it's coolant at 108C which is 225F. I'll be changing that this spring - and I'll post how I do it with minimum of hassle, etc. Otherwise, thermostatically controlled or not, I would be surprised to see under 210+ trans temp on a hot summer day..............

[Turbo_Bimmer]

Civdiv99, I have a diagnostic tool to read the transmission temperature sensor. If this is helpfull to you, I could connect my laptop tomorrow while going to work (30 min highway drive) and let you know the max I read.

I read somewhere that the ZF fluid is expensive because it is formulated to be non-conductive since many electrical connectors are submerged in the fluid.
I would be curious though to take a measurement between the ZF stuff and M1, just to see.

[RRPhil]

Civdiv99,

Here’s a typical result from my Range Rover (M62 engine, ZF5HP24 transmission, same cooling system as E53). 110 deg.C. = 230 deg. F.

Clearly the fact that the electric thermostat on the engine operates the engine cooling system at such high temperatures in an attempt to eke out the last bit of fuel economy at part load doesn’t exactly help with the transmission fluid ‘cooling’ (or is that heating?)



Phil

[Ghost-Flame]

I don't have any data just some thoughts.

I always thought that tran fluid temps of 220f to 230F were normal. You are running 150F with the added cooler. that's 70f. I would think that would be great for extending the life of the trans.

[SlickGT1]

I don't know if I will ever put in a cooler again.

I used to think they were life savers, until 2 cars I put it in, the trans died months after. I came to the conclusion that modern cars cool the trans enough as is. I also have a theory that adding cooling lines for the additional cooler reduces line pressure throughout the system. At 200+ deg, tubing and lines will expand and start changing oil levels along with oil pressure. With the transmissions being the sensitive drama queens that they are, any pressure, volume differences might cause more damage than good with a cooler.

There are guys on ClubLexus that are currently working on hard line cooler systems for the same reasons I am stating. (I don't know why though, as I have very rarely seen a trans fail on that site, I know mine lived a happy life with heavy abuse).

I say don't mess with it.

[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.