I wrote the article before I had the drawing. Gary's right, it's not an exhaust deflector, it's just a deflector on the early version for the M4A3. Although the later parts are called exhaust deflectors, but the exhaust is not just the engine combustion exhaust, but also the cooling air exhaust.
None of the initial M4 series tank designs had any provision for any deflectors for exhaust air, which caused a serious tactical and technical problems caused with all of the dust that got kicked up. All of the M4 series then had deflectors added to them. The M4A3 was one of the first ones to have the feature added.
Notice the missing parts on the tank I took pictures of for the article. The locking pin is a prominent part that needs to be added. Incidentally, the part in the article went on to Rob Ervin at Formations.
As for warming up. I am positive that that is what these two doughs are doing.