Before winter hit, the coolant tested at -35 degrees F. I guess possibly I could have gotten a bad cooler. If it could happen, it could happen to me. Seems like the thing cost just a little over $400 directly from Cummins. Do you know of a way to test the cooler? I've about decided to rebuild the thing. I know it doesn't have many miles on it, we've got a '99 and a 2003 model that both have around 200,000 mile on them, with no internal engine problems as of yet (knock on wood). But this truck sat for 5 years (from 2000 to 2005) with a messed up front end. I think the sitting was harder on it than anything, as it has multiple oil leaks, and more blow-by than I think it should. Also, i've noticed lately, it takes several seconds before the oil pressure builds up after you start it. Especially on cold starts. So I was thinking all new gaskets, seals, set of rings, rod and main bearings, oil pump and head stud set. Plus have the head checked out by my machine shop. I know it won't be cheap, but I've got a big shop, tools, and I'm capable of doing the work myself. We've rebuilt a 5.9 before (D41 Komatsu dozer), and it wasn't that bad. Am I on the right track here? Right now, money IS an object, but it's an object that's going to have to be overcome, so from a mechanics point of view, what would you suggest with the blow-by and oil leaks in mind? The reason for the head studs, while this isn't a hot-rod by any means, it is turned up a bit. I haul a Case 580M and a 580Super M on a pretty regular basis, plus it's rigged as a welding truck, so it's not light on it's own. Thanks for your replies.