It would be great if that transpired to be the origin of that phrase!
Class 40's were ice boxes on wheels, the doors fitted where they touched and the windows kept slipping down.
They were full of expanding foam to stop the hurricane of cold air which blew in through every nook and cranny of these engines,
As someone remarked, the stove was in the middle of the engine compartment.
Before leaving HM, I placed a can of boiling water on such a stove to go class6 to Manchester.
On arriving at the location after about 45 mins running, I went for my boiling can, but alas it was full of cold water by this time.
The comedian who decided that the mashing ring was in the engine compartment, ought to spend the rest of his days riding about in such an engines gasping for a quick brew.