04 LB7 with 200000 miles using coolant. Dealer also says they have found a couple instances where the coolant cap had gone bad.

Is coolant level low, very low when that happens. A collpsed hose and low level in the fill/overflow tank when its cooled off indicates you have a leak externally or into the crankcase. If the tank fills and overflows when running its an indication there's a compression leak into the coolant.If that capleaking, there shouldn't be any vacuum to collapse the hose.Your dealer knows all that and to say its the cap sounds like a lame excuse. Let us know what you find out, maybe we can all learn something.

If you have a coolant leak, it seems nearly impossible to have a collapsed hose, as there wouldn't be enough vaccuum to make the hose collapse. There is a chance that your cap isn't holding pressure allowing it to leak out the overflow tank when the coolant expands, and the vent is plugged, not allowing air back in when the coolant cools down. As long as you don't over fill the overflow tank, it shouldn't push out any coolant, unless you have a head gasket or injector sleeve leaking compression into the cooling system. I would try a new radiator cap, fill the overflow tank to the "full cold" line, and keep an eye on it. If it keeps pushing out coolant, then you'll have to dig deeper.

I posted a "collapsed hose" thread a few weeks back. I had also been adding fluid about every week. Last week, I was hauling some heavy loads and barely making 30 miles without having to add coolant. Finally spotted the drip,drip,drip coming out of the water pump weep hole on Saturday. Let the truck sit all weekend. Got ready to take it in this morning and when I went to fill the tank, the hose was collapsed again.

Take a real close look at your water pump weep hole. It is right above and behind the lower hose. You may have to move a small wire out of the way to see it.

Oh ya, 103,000 miles on truck

Its going in today. Usually, a leaking water pump means it is bad, buut mine has never overheated. No oil contamination and no water in the exhaust. Just one of the many things wrong with it.