Re: 498 and 488 approaching Cumbres with the1963 RMRRC excursion

Running "in the britches" without opening the drifting throttle valve will slow the engine, as you are simply compressing the the air in the cylinders. Things get real hot real quick. Adding the steam from the drifting throttle cools things a bit, not much, but a bit.

I remember coming off the hill light one afternoon. When I opened the drifting throttle steam started squirting out around a pipe union next to the valve. Lacking two big pipe wrenches to tighten things up, I simply closed the drifting throttle valve and hauled the Johnson Bar back a few more notches and gave her a bit more tender brake. I could smell the valve oil cooking out front, and as John pointed out when you put the engine back into forward motion, the Bar racked hard in the quadrant until some oil got pumped into the valves. It was a pretty slow trip down the hill after that.

I've wondered what the cylinder temperatures and pressures are when you come off the hill with the drifting throttle. The mechanical lubricators can generate 400+ lbs of pressure. But even that isn't enough to over come the cylinder pressures. Superheat valve oil is good for 750 degrees or so.