I have a "built" 500 cubic inch Cadillac engine that I am running in a 1940 Chevy truck.  I am running an Afco aluminum radiator to fit the stock location.  I am using the cadillac 195 degree thermostat that blocks off the bypass when open.  I believe the water pump is made by "Flow Kooler".  I also have the stainless steel radiator hoses.  I added a 4000 rpm fan and shroud from a Lincoln.  It is the perfect size for the radiator and immediately brought my cooling temps down to 195, even on a 100 degree day in traffic.  My problem is that I had been running a mostly open exhaust.  I recently had a pair of magna flow mufflers installed.  On the drive home from the exhaust shop, I noticed the engine temps rising again.  20 miles of highway driving brought it up to around 230 degrees.  I also had the air conditioning system charged for the first time, but didn't run it due to cooling concerns.  I may try drilling some small holes in the thermostat to reduce restriction. My two questions are:  Would a triple pass radiator cool any better than the 2 core aluminum Afco that I have?  Do you have any other suggestions that could help my situation?

Thanks for the response.  I'll go back through the truck and "fine tune" the cooling system.  At least now I know not to spend more money on a different radiator.  I think I may be able to tweak the airflow across the radiator a little.  I'll go ahead and try advancing the base timing a few more degrees, and double check the centrifugal and vacuum advance.  Hopefully a few little things will be enough.  I was considering trying the Evan's coolant, but I wonder if it actually enhances cooling or only eliminates the boil over caused by overheating.