Overheating Mystery

[sdcfish]

Can't figure out why my 350 engine is overheating. Bought this 55 Bel Air from my cousin. Had been re-built 2000 miles ago using a Summit Racing Performance Kit...Stage 1 Cam, High compression heads, edlebrock intake and carbuerator, headers....runs awesome if I could keep it from climbing up to 240 degrees!

Found out that the radiator was trash....super rusty inside. Car had been sitting and not being driven for a long period....maybe a year or more.

I added a Champion radiator...aluminum. Added a new 14" 2450 CFM fan, new shroud, and new water pump. I have tried running the car with and without thermastats. No luck!

This is what happens. Car runs very cool with no thermastat for about 10 minutes...mabye even 15 minutes.....stop and go traffic, waiting at street lights etc...not freeway driving.

Slowly, the engine creeps up to temp....I mean a long time I imagine is 15 minutes....4-5 miles of slow stop and go driving....so seems to be holding at 190....200.....but then boom! The car goes to 205, 210, and keeps climbing slowly.

I have recenly soaked the engine and new radiator etc in CLR, Radiator flush....even Vinegar! 2 days of vinegar.....1 day of CLR.....3 days of radiator flush. Went today for a pressured radiator flush...vacuum and pressure...so backflushed, and forward flushed, and replaced all fluids. Took off the electric fan and shroud, and added a bolt on blade fan....seems to be pulling more air, but no shroud yet and it's super close to the radiator, so that's a problem.

But test drive after the new fan mod, and pressure flush after 3 days of soaking the engine and still doing the same darn thing....just a slow increase of delayed temp rise, and then overboard. Still no thermastat in the car.

Could it really be just a fan shroud needed at this point, even though it's still doing the same thing with heating up over such a long, slow time?

Im really looking for help. I have no water in the engine oil. I puff no smoke out the tail pipes....engine runs really strong...love it!

What else can I look out before throwing in the towel and stripping the entire engine down?

Thanks for your help......Im attaching some pics of the old radiator and water pump that I have removed to give you idea of what I was looking at when I started replacing stuff.