My 05 WR450, has a distinct odor that I notice when it is running, I think that somehow some coolant is working it's way into the upper end of the engine, but I had a local shop do a pressure test on the radiator and the mechanic said that it held pressure. Nontheless, I have been losing some fluid from the overflow tank, not a significant amount. I did a search but wasn't able to find much information about what I might do about this. We have several aluminum block chevy engines and they all eat coolant, it doesn't seem to do much harm, there. Auto parts places sell some pellets to add to the radiator to seal up the leaks, and this was recommended to me by a retired GM engineer. ????? Probably won't do much until this winter, but may take off the head and check for warpage, and replace the head gasket at the very least.