A couple of months ago I started my 239 flathead for the first time after an overhaul. I did not have a fan shroud at the time and my water temp after tuning up and messing with the engine for about two hours was a steady 180*.
I just bought a used shroud from Josh Madsen on this site (thanks Josh) and now the temp is down to as ready 160*. What a difference!

 

I agree, it's as important as a thermostat! Plus I just don't like having nothing around that spinning fan. Too easy to get just a little too close.

 

You can bet that if the fan shroud was not necessary, the manufacturers would not install them. And of course, you'll find the naysayers who don't run one and get by just fine. It is all about maintaining enough airflow through the entire surface of the radiator. I ran a '52 Merc for a about year without running a fan. Of course, I did not run in traffic and judged my stops.

 

Fan shrouds are very helpful at idle and at low vehicle speeds. However, you really should run your engine at 180 F. Engine temperatures lower than that don't get the oil hot enough to remove any moisture and let sludge build up.

 

Cool! Glad its on and working.

I put 190 thermostats in the flathead in the 53 C600. I really need to ad a mechanical gauge so I can see what its actually running at.

In March pulling (very slowly) a parade float it goes to the hot side and does not move either direction so its steady and hasnt boiled over. Of course the temps were around 65 or so, need to see how it will do in the summer heat I guess. It has a shroud on it as well.