Hi Paul, the big problem I have discovered here is there is not a coolant over flow bottle/tank installed......so when the coolant heats up and expands it just goes to the ground from the drain hose till a hot coolant level is established. Now if there are no leak's in the system, when the coolant cools, the level in your surge tank goes down to around the sight glass level, leaving half of the tank empty......allowing for rust to form it seems.....
My surge tank is completely full all the time and there is a level in the over flow bottle at all times that goes up and down from coolant expansion and contraction.......cold level/hot level.
So, I have asked before on here with not to many response's, why not add a expansion tank so the radiator cap drain/over flow hose goes into the tank.......so your surge tank will always be full and the level in the expansion tank is a lot more easier to look at and if you watch the cold/hot levels, you can quickly see when you are loosing any coolant at all.........
I am going to say, due to added cost is the only reason these Coach's don't have them when built..........?
Just a thought for you to ponder......
I just replaced mine last year as it was old and a couple of the mounting points broke off. Bought a exact replacement at RV Chasiss.com(Spartan)
https://www.rvchassisparts.com:8443/...is/runApp?id=5
No reason that I can come up with not to add one............
Same coolant system setup as most all auto's and even big trucks/semi's.........as most radiator's are not accessible today and all use a "Overflow" Tank.