Thinking I will do a coolant change on my 35 pick up. Is there anything to be aware of when flushing out the radiator and block. Do I just take off the top and bottom hoses and go for it? Sorry still a noob at flatheads.
I tend to use non glycol coolants as it doesnt "search" for cracks like glycol.

 

Talkwrench

If your rad is the original type and it has never been recored then it has the rods in it. the only correct way to clean it is to have the top tank removed and there is a wire brush that has to go down the rods or tubes to clean the scale.

If your rad is again the original type and is in good condition then run some vinegar through it with distilled water you can get from the drug store its pretty cheap and doesen't have the lime content in it. I would run the vinegar about 50-50 mix for awhile then drain the rad and then use the distilled water with antifreeze to required mix.

Also there is a product called Iron Tite I've used this in rebuilds and it will go to and seal any crack if there are any. But DON'T put it in the rad. Take off the top hoses at the heads and pour 1/2 of the bottle in each side, replace the hoses and top off the rad to just a little above the core.

This proceedure should be done on a warm engine. some guys fill the rad to the top and this is wrong, as when it gets warm and the coolant starts circulating the rad will spill its fluid all over and make one hell of a mess. That tank on top of the rad is called an expansion tank and that is exactly what its intention is. Works the same or similar to a coolant recovery tank on the newer vehicles, 1960s and up.

Hope this help you out a little

 

Normally I would pull the radiator, but it looks like a bit of a mission on these to get it out. Since the motor has been [suppposedly] rebuilt I am expecting it to be half decent, I'll see what crud comes out, If its real bad then I'll pull it and go through it properly.
So who runs thermostats??

 

You pretty well have to run thermostats in a Flathead, or a large fender washer with a 5/8 hole so as to restrict the constant flow and also to let the rad do its job of cooling.

I spoke with a man in the desert country of Las Vegas NV. he has an original 1937 Ford Flathead and he runs 180 thermostats. He told me his cooling system is clean and he has no issues with over heating running the dessert. I've been down their in 115 degree temps its hot.

I had an old timer who used to do the Rad Rodding tell me that 180s were the ones to use. some use the 160s and in reality their open most of the time allowing full flow and therefore the rad isn't keeping up with the cooling.

 

Check out Alconox. We used to use it at the Ford Dynamometer Laboratory for cleanuing the dyno heat exchangers (Liquid/liquid radiators). Powerful stuff.

Alconox® Powder Detergent And Precision Cleaner - Spi Supplies | SPI Supplies