Buick 350 in regal not keeping cool

Has this 350 been bored out? If so, that generally requires more cooling capacity. I am not familiar with the fan you mentioned, but it should be moving a TON of air if functioning correctly, just like a stock mechanical fan does. I'd check you don't have an air pocket in the top of the engine too.

You have a problem here and it should be easy to explain, just have to get your hands dirty and figure it out.

I 100% agree with Larry in regards to the thermostats.:TU:

 

thing that contrays with a keeping the coolant in the radiator longer also means the other half of the coolant sits in the block longer meaning it gets hotter....not?? 2 other thing thrown out there from other guys could be a

bad head gasket- but there is no oil in the coolant or milky oil

Lean carb mixture- one way to find out. pull the plugs

I thinking of trying it with out the thermostat (Mr Gasket 160, it tested fine in a boiling pot of water, but if you do a search a lot of people had problems with them) to see what it does. Really it should keep cool without it, if it does not time to look at something else.

 

... so, the carburetor isn't running waaaay too lean?

 

My advice is before you start tearing things apart and throwing money at it, make sure it's TUNED PROPERLY. This alone might be your problem. Once that part is out of the way, then you can progress to the rest of your processes of elimination.