I'm not sure yet if I'll end up modding my current enclosure to fit a single 10", or go some other route. Either way, I'm not selling it yet as it is part of the current system until I decide what do to. I'll let you know if/when it becomes available.

I'm pretty sure that's the issue. I sourced the water pump and thermostat from eBay. I think I paid $80 for the water pump and $55 for the thermostat. Lesson learned. Both eBay vendors had good ratings, but I guess that can be very subjective. Thermostat guy did give me a full store credit, but I doubt I'll use it. Water pump vendor offered a full refund, but I didn't have the time to pull it have him receive with within the 10 days allowed.

Like I said, lesson learned. Should have done some more research here on this forum before ordering those items.

Tons of reputable OE sits. Pelicanparts, AutoHausAz, RME, etc.

Hell, even the part # for the water pump from the dealer, is a Refurbished Core unit....

Good luck. For hoses, gaskets, etc - Dealer. Getbmwparts.com
For the rest, cheaper options on the OE sites . SOMETIMES even better IMO when looking at suspension options...(more bushing selection)

Tons of reputable OE sits. Pelicanparts, AutoHausAz, RME, etc.

Hell, even the part # for the water pump from the dealer, is a Refurbished Core unit....

Good luck. For hoses, gaskets, etc - Dealer. Getbmwparts.com
For the rest, cheaper options on the OE sites . SOMETIMES even better IMO when looking at suspension options...(more bushing selection)

Good info on the aftermarket parts, Stunt.

I get mine (mostly) from FCPEuro.com So far so good.

As for your sub project (assuming you ever want to touch the X5 again after this massive project), I had surprisingly good results dropping in ever so slightly modified (trim the mounting rings a bit) a pair of JL 6" subs. They go down pretty low -- low enough to feel the bass on London Grammar's "Hey now". Pretty musical too, picking up the low end that the HAT Imagine's leave off in the front. Not the best, but nothing to sneeze at either. Minimal modification to the stock housing.

I'm assuming you no longer have the amp that is looking for a 2ohm load? I imagine replacing 2ohm speakers with 4ohm would significantly affect the sound output.

ebay is only good for finding hard to locate USED items, not new.

Okidoke, add it to the tools for whenever list please.

If you run a dual voice coil 10" you should be fine... but the trick is going to be finding a 10" sub that will work with the power output of the am in relation to the volume of the box ;)

keep up posted stunt! I've been thinking of trying the same thing in mine since I bought the truck...

This is the sub I was looking at:

http://www.jlaudio.com/10w3v3-2-car-...-drivers-92150

Rated for 500W (same as my amp) and the optimal sealed enclose size is 0.625 cu. ft, which I think is very close to the volume of the factory unit, especially modded for a single 10" hole via a piece of MDF wood.