Transmission Heat Exchanger

[imbvl]

I use my 4.4 X5 to pull a boat, sometimes. Not a big boat, maybe 2300 lbs., boat, motor and trailer. (With 300 hp and full-time 4-wheel drive, I have no problem pulling the boat up a slimy ramp!) If it's a hot day (here in Florida) and a long trip, the transmission refuses to shift, and I end up going down the highway in 3rd gear at 3500 RPM. Other threads lead me to believe that the transmission heat exchanger is not doing its job, and the tranny oil is overheating. Is there a DIY thread on this problem? Can I just remove it, flush it out, and replace it? It's $350 for a new one.

I've ordered a BMW TIS on EBay, but it hasn't arrived yet. It's not apparent to me, what holds the cooler in place. Maybe the middle cylindrical thingee on the front side?

The tranny was replaced about two years ago, with a factory re-build, so I don't think it's a tranny problem.

I can obviously take it out, figure out the problem, take some pictures, and write a DIY thread myself, but I'd rather not invent the wheel, if I don't have to!

Thanks!

Bruce

[racingbmwm3]

Its a coolant to oil heat exchanger. I can't imagine it ever needing replacement unless it has physical damage.
The engine is running normal temperature at the time?
Considering the conditions you are running in, maybe a larger aftermarket air cooler would be of help.
And maybe new transmission fluid including flushing the lines would also help. I'd also change your differential and transfer case fluids more often.

If you do remove the cooler to clean it, you HAVE to replace the sealing rings else they will leak.

Also, you don't have your vehicle in your sig, so nobody will know which engine/transmission you have without knowing the model year of your X5.

[imbvl]

ATF-to-water heat exchanger - understood.
Normal running temperature. It's happened twice now, while hauling the boat. Other forum posts indicate that happens if the tranny gets too hot, because the heat exchanger isn't working effectively.
Tranny fluid changed two years ago, when the transmission was replaced. No fluid leaks from the tranny.

I'll take pictures of my cars, and post them. Thanks for the reminder.

I ordered the BMW TIS CD from EBay; less than $20; hasn't arrived yet. all will become clear, I'm sure.

Thanks for the response!

bruce

[g300d]

I did replace mine on a 3.0 but I believe they are pretty much the same as the v8's. Not the same problem as yours though, I had oil in my coolant and it was a last ditch check before a tear down. A pressure test showed a leak in the cooler so I thankfully did not have to open the motor.

There is a mounting/water distribution plate attached to the radiator. On this plate mounts the coolant reservoir tank and the transmision oil cooler, via the peg and its coolant inlet/outlet lines. It is a heat exchanger as mentioned.

It can be accessed from the bottom of the car. Remove covers, pull the wire clips securing the coolant inlet/outlet lines and the mounting peg, then wiggle the cooler a bit while pulling. It will pop out. The cooler will hang down and you can now remove the transmision oil inlet/outlet lines. Or you can do it vice versa and remove the trans oil lines first as those "quick connect" oil lines can be a pain to remove sometimes if you dont have a place to push against.

Another place to look if you suspect trans temp problems would be the transmision thermostat. On the 3.0 it is under the coolant reservoir tank on the mounting plate, not sure about the v8's but I suspect in the same area as well.

[racingbmwm3]

How many miles since the transmission was replaced? When did the shifting issue begin happening? I'm still not sure replacing the cooler will correct anything. I'd look into an auxiliary air/oil cooler. If the problem started happening recently, then your tranny fluid has probably broken down from the heat just enough to cause the issue.
In extreme duty circumstances, your case being high loads in high ambient temp, transmission flushes would be called for more often, similar to the maintenance performed on cars driven on the track. Typically, all drivetrain fluids changed annually, engine oil every few track days. One day of towing possibly equivalent to one day at the track??

To check the function of the stock cooler, I'd disconnect the lines at the transmission and flush clean fluid through one hose and see if it comes out the other hose just as fast as you pump it in.

[civdiv99]

The instructions you got for removal are spot on. I'd only add that I'd plan for some locking pliers to clamp the coolant and trans lines to prevent a bath.

But I doubt very much you will find an obstruction. Not in the trans fluid path, else you would have issues 24/7. And if you have coolant obstruction from deposits, I venture to say you have bigger issues, such as radiator.

Check also fmugar's posts about the radiator design and quirks affecting trans cooler efficiency.

[imbvl]

Thank you all, for your comments. Very good comments!

I bought a TIS DVD on-line, but haven't completed the downloads, yet. Not a slam-dunk.

I removed the oil-to-water heat exchanger, leaving the oil lines attached. Back-flushed it with a garden hose; no obstructions, no deposits came out. Good to go.

Then I removed the thermostat. There's a little (10 mm?) diameter piston, visible inside. Couldn't move it with a screwdriver, using moderate force. One end of it comes apart easily, held in with a spring clip. Took a sharp rap with a hammer to break it loose. Bought a new thermostat - $75. I found that when I had disassembled the thermostat from its bracket. one of the bracket fittings that the thermostat slides over had broken. Bought a new bracket, too - another $60. Put it all back together, ran it, checked for leaks - none. YAAYYYY!

Hooked up the boat and trailer, dragged it 50 miles on a 78-degree day. Problem came back - wouldn't shift out of third after about 50 miles. I pulled over, shifted into manual mode, and took off again. 1st to 2nd OK, 2nd to 3rd OK, wouldn't stay in 4th when I shifted it - went back to 3rd. 4000 RPM at 43 mph is not a recipe for long-term happiness, for me or the truck.

Back to the forums!

[admranger]

I've heard rumors of clogged heat exchangers from crud in the radiator blocking the passages.

Not sure if these rumors are true or not, but I recommend a radiator flush before you put in the new heat exchanger.

[imbvl]

The radiator and block were flushed thoroughly, when I replaced the head gaskets and chaintensioners a few months ago. Water system is clean. No crud came out of the heat exchanger or the thermostat, when I flushed them.

Thanks for your input, though, Kirk!