Anyone pulling a 19' with BMW X3?

[jcl]

Originally Posted by adamkalins

I understand the new X3 have more engine power, but look for that second transmission radiator, or have one spliced in, or drive 80km/h,.....

A cautionary note about adding additional transmission cooling to these vehicles. The older X3s used GM transmissions (5 or 6 speed). Newer X3s use the ZF 8 speed transmission.

The ZF transmission uses an oil to trans fluid heat exchanger to cool the transmission, and it is equipped with a thermostatic control. This is a more sophisticated system than simply a fluid cooler stacked in front of the radiator. The system works in both directions, providing cooling in higher ambient temperatures, and heating the transmission when the fluid is cold. Turns out a significant amount of transmission wear happens after a cold start before the fluid is warmed, and since engine oil warms up faster than transmission fluid, the engine oil is used to heat the transmission fluid until they come to equilibrium. The transmission has a special cold shift program, based on fluid temperature. It is not advisable to over cool the transmission. Removal or bypass of the thermostatic valve can result in the transmission staying in the cold shift mode for an extended period of time.

Any additional cooling should be done with retention of the thermostatic control for transmission fluid, IMO. I would monitor the fluid temperature, but wouldn't recommend adding an additional cooler.

[BayouBiker]

Great advice JCL! Another sound piece of advice would be to not push the manufacturers capacity limits. They know their vehicles and capability very well. One upping or second guessing manufacturers engineering teams is often a fools errand. Many people learn this lesson too late.

[jcl]

I would simply reset the light on the dashboard, using a code reader instead of gum.

[adamkalins]

I had an ODBII sensor watching it, and the coolant was at the expected 195-210F range. The car never went into limp mode, it was just so crazy hot. Yes I noticed that the engine coolant was always where it was supposed to be, but I think that the heat exchanger was not moving the heat to the radiator effectively. The sensor messages were all from transmission places and all had temperature in common. The transmission oil meets the engine radiator at a heat exchanger, and thus cools the transmission oil. Even though the radiator was reading OK, I think the oil was not exchanging heat at a high enough rate. I have since learned a lot about heat exchange. The engine needed cooling, the transmission needed cooling, I was pushing a lot of heat at an old radiator in the summer. The ambient air was thin, dry, hot. The low temperature delta and low absorptive quality of the air combined with my high production of heat (towing max) I just rode the limits of that car for probably half the vacation. If anyone is reading this, the lesson is that if your car says you can tow 4400lbs (thanks bono) then you can't actually tow 4400lbs. Your car is not new. Your family will pack too much. You will want to accelerate uphill. You will want to go above the speed limit. Mountains have less air. The praries are dry. Summers are hot. Bono, I have an X5 now too. Much nicer. Much. It has a separate radiator for the transmission and I can barely feel the Airstream behind me. This one time I floored it off the line (because I could). All the dishes, everything that was in the trailer, was sent to the back. Good times.

[BayouBiker]

The integrated radiator transmission coolers are have limited transmission fluid to coolant heat transfer area. If the transmission is generating more heat than can be conducted through that area, the fluid will heat up while the coolant does not until the temperature difference is sufficient to force the heat energy through. As the radiator ages, fouling on the exchange surface makes the issue worse. This is why vehicles designed for heavy towing and hauling have large separate coolers for the transmission. As you learned, manufacturers recommendations are there for a reason.

[jcl]

Originally Posted by BayouBiker

The integrated radiator transmission coolers are have limited transmission fluid to coolant heat transfer area. If the transmission is generating more heat than can be conducted through that area, the fluid will heat up while the coolant does not until the temperature difference is sufficient to force the heat energy through. As the radiator ages, fouling on the exchange surface makes the issue worse. This is why vehicles designed for heavy towing and hauling have large separate coolers for the transmission. As you learned, manufacturers recommendations are there for a reason.

The heat exchanger system used on the ZF transmissions has proven to work very well. No additional cooling capacity is recommended to be installed.

In the case being cited:

*the vehicle was towing a load within its rated tow capacity
*it appears that the vehicle may have been overloaded, with passengers and cargo, but we don't know weights.
*the vehicle was an older model, and it was reported that the radiator was dirty
*it was reported that nothing failed. A light came on on the dash, which the poster resolved with a piece of gum stuck over the light
*the vehicle was being operated at higher speeds than it may have been capable of, given the older 2.5 l engine model, and steep ascents
*the vehicle experienced very high fuel consumption, suggesting that it was working hard
*the replacement vehicle was a newer and larger BMW SUV, with the same heat exchanger design. It was reported to work very well

Lots to learn here, including loading to rated weights, maintaining a vehicle and cooling system, and so on. I wouldn't put cooling system design in that list.

[BayouBiker]

Repeating good observations is a virtue.