Overheating in traffic

A few possibilities I can think of (others may jump in with more ideas)

No anti-collapse springs in the radiator hoses, sucking flat or close to it, tight bends

Radiator is not new/ maybe it needs professional flushing?

Is there a shroud for the fan?

This is just one of many products, have you tried any? Link below.

https://www.summitracing.com/parts/kys-530-4032?seid=srese1&cm_mmc=pla-google-_-shopping-_-srese1-_-keyser-manufacturing&gclid=Cj0KEQjwzpfHBRC1iIaL78Ol-eIBEiQAdZPVKsd_QNh-lcTJ6mhAdylZe_OptlnsKMZbU2ZI5IJwKlwaAp1F8P8HAQ

I reckon you have a fixed fan and are not using a fan clutch (fan clutch could be bad)

Here's another trick that may help.

See my last reply in this old post/ click on the pics and compare

https://www.2carpros.com/questions/1961-pontiac-other-1948-6-cl-getting-too-hot-215deg-just-blocks-driving

Your turn,

The Medic

Coolant should NEVER be more than a 50/50 mix as it eats aluminum up. What is compression ratio on engine? If higher like 11-1 will cause it to run hotter, 210 isn't to bad to run a 455 try a bottle of water wetter, or the stuff for cooler running at auto parts that works. You may want to invest in an electric water pump as well.

I've sued the coolant help stuff before and it works. Not necessarily that brand though.

HMAC300, Took me a few seconds to figure out "sued" was spota be "used"!

I too have had good results with a different brand, called somethingoranother COOL or COOL somethingoranother, I couldn't find it online at the store I got it from a few years back.

The Medic