This is a good subject. I bet more of them aren't working correctly, but most people would never notice.
On the vegistroke forums this has been a hot topic for discussion. The 6.0's have notoriously had poor coolant flow since the vegistroke came out. With that kit, you're relying on coolant flow from the engine to run back to the bed, through the aluminum tubing in the tank and back up to the motor, to heat the oil in the tank. Almost every 6.0 owner with this kit experiences poor flow and poor heating in the tank. Despite the kit using 3/4" lines and the 7.3's using 5/8's, the 7.3s never had this problem. With my setup I always had VERY poor coolant flow. The line going in my tank would be luke warm, and the line coming out would be ambient. To remedy this, a bunch of guys would buy an aux coolant pump to put in line down on the frame to help push hot coolant through.
I just had my truck gone through over the winter to do studs/gaskets etc... when it was torn down, I did a new OEM thermostat, and I went with an Alliant water pump. It has metal impeller blades on it, vs. the OEM plastic. I also had a new radiator put in (trans lines were rotted and didn't come out very nicely, and cracked the original). Did a coolant flush, new OEM oil cooler and put it all back together, still using Ford Gold coolant. Wouldn't you know... coolant lines running to the tank in the bed now... HOT going in and HOT coming out. I now have EXCELLENT coolant flow. I also monitored my temps before and after and EOT and ECT remain virtually unchanged, despite the poor flow before.
Many people with coolant filters have found black plastic pieces in their filters... parts of the OEM impeller. Others have found they spin on the shaft at times and become useless as well. I couldn't justify going with another plastic OEM unit myself. I'm glad I didn't, now I shouldn't even have to worry about adding that aux coolant pump on mine to get the proper heat for my veggie system.
