The locomotives at Saint Patch Grade, that means the SD40-2, GP38-2, ES4400AC, created clearly visible exhaust when the engine was running. In my opinion this exhaust rather looks like steam so I always get the impression that the engine must be broken and burns its coolant. The exhaust should look less white, more grey and more translucent than the present white "clouds". But after all, the CSX locomotives have exhaust! But when I'm driving on a Class 66, Class 166, or Class 43 I absolutely cannot see any exhaust. I know that the locomotives have to meet very hard emission norms, which might be a reason why there is not as much exhaust visible as on the CSX locomotives. But especially the HST, build in the 1970s, when emission laws were less strict, should produce visible exhaust. The Classes 166 and 66 were build in later years, but nevertheless I cannot imagine that there is absolutely nothing coming out of the exhaust pipe. At least some flickering air should be visible.