Liability-rated by marketing for the USA is the same as the weak-sauce 3.7l V6, 5k lbs. However, the EXACTLY THE SAME European version is rated at 7k lbs.
When properly equipped, I have pulled that 7k lbs without any problems, and stopped it as well.

The best was getting 19mpg while doing it!
I'm probably the person most likely to be voted "insane towing fool" b/c I've equipped my CRD with a pintle hook, and actually USE IT for hauling really heavy stuff like this:
That is a 70kW generator equipped with its own hydraulic brakes, weighing in at 6840 lbs. With the 4500 that the CRD scaled at... That is 11,340 lbs being pulled at 19mpg by a FOUR CYLINDER ENGINE!
Take that, Mr I-Gots-a-Hemi driver! Bwahhahahahhahahahahahahahahahaha!
