Pay attention to your trailer brakes. Our 23' Yamaha only has brakes on the rear axle. If I lived in CO (rather than FL) I would add them to the other axle immediately. Brakes on both axles are required by law in many states (including FL) but the boat dealers sometimes ignore to save $400. Also, flush trailer brake fluid often.

I find the X5 transmission will stay down shifted when the transmission starts to get warm. That must pump fluid faster to cool things off. After a minute things go back to normal. It is a nice warning sign.

As ard mentions, Android Torque with a Bluetooth dongle in the OBD port will allow you to set up a custom gauge set to monitor temps.

And are you sure your boat weighs 4000lbs? My very light 23' boat weighs 3200 empty. Add 1200 for trailer. Then another 500 for gas and gear and I am near 5000 lbs.

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2009 35d, 2006 325i & 330i