Not condemming anyone, just pointing out simple things. Butnuts are some of the most creative folk I've ever run into when it comes to solving problems, or should I say, overcoming various challenges - chassis & house both.
FYI, All of the coaches I drove over those years were stock, often fully loaded w/ passengers & luggage. MCIs are the most notorious for overheating stock cooling systems in our hot SW deserts, stuff a "monster motor" in the tail w/o any other changes and it was a recipe for disaster. And some charter bus operators tried just that - I even had to go out a couple of times to rescue their passengers. Not a pretty sight when you've got 40 people stranded by the side of the road in the middle of the Mojave Desert. The company I worked for had a strict policy that if you overheated and shut down due to driver negligence, you were headed to the unemployment office. You learn quickly under those circumstances!
I think you'll agree that if you stuff a 454 big-block in a Chevette, you're going to have problems w/o a lot of modifications. Extreme example, but you get the idea. Even Geoff, whom I have tremendous respect for, admits that adding the additional load of his trailer/toad to his coach taxes the stock
cooling system. So solutions have to be sought, as has been done.
With the two-stroke Detroits, the sweet spot for pulling grades seems to be in the 1700 - 1900 rpm range on a partial throttle. Running it on the governor with black smoke pouring out the tailpipe is guaranteed to overheat the beast. The Series 60 has a sweet spot that's several hundred rpm lower - TomC probably knows the range and can chime in with the numbers. The key? "Partial throttle!"
I guess my major point is this: Most busnuts overheat their coaches because they're pushing too hard for the conditions and
not paying attention. Otherwise known as my tongue-in-cheek comment about excessive weight in your right shoe.
Perhaps the above helps explain why I often talk about Aesop's Fable of the Tortoise and the Hare. Buses are not hares, yet owners often try to drive them that way. Those who do end up with various problems, asking for solutions. Those who drive their coaches like a Tortoise, arrive unstressed, happy and ready to roll again next time.
FWIW & HTH. . .