[Guy]

Yep. You nailed it Clarke. After having a large  leak in the next compartment forward last winter , I am paronoid about such things. At some point (soon) the hose has to be replaced. It has several pinholes that oooze coolant The prior leak in the foreward compartment was caused by a broken  manifold that joins the in cab heater, water heater preheat lines and this mystery loop, which is an abandonded loop. I think as Tom surmised,  it is from a former water bay "en route" heater. Who knew that these old coaches had a means to keep the water bay and storage areas toasty while driving in freezing weather ?

I have no interest in resurrecting the old storage bay engine produced heat system, but do any Classic  owners have a system remaining? Just curious, Would love to see how Newell engineered  it .