OVERHEATING

things not mentioned
wrong cap:- short spring cap in long spring filling spout
loose cap bend over the tangs
system never builds pressure it doesn't necessarily puke but the coolant miraculously disappears.

header tank of radiator below the highest point in the system leaving a big chunk of air in the heads..... you get the same symptoms ????



1) it overheats at a point way past the fan doing anything uesful so not fan
2) it doesn't overeheat on the fan which pulls through such a small amount of air compared with driving at speed, so if the fan can suck enough air to cool at idle and low speed i'd suggest the radiator is potentially ok
3) sounds like under driven pump is in place, this is usually a good thing. if the coolant goes too fast through radiator the coolant doesn't dump any heat. hot radiator hot engine very little heat energy removed. it just recycles it. same happens with no stat in place and you have one in there. all good.
4) evans everlasting radiator goop carries less heat energy per pint than standard blue coolant. it just doesn't degrade in the same way. it comes down to "specific heat capacity of the coolant and its ability to wet the metal surfaces and as far as i can tell evans' isn't any better than standard, and is possibly worse on this front than water and glycol. it behaves differently which could be considerd a benefit but if it was as good as they say military and GM Mopar and Ford would be using it. They may be. but i don't think they are

what i can say is swapping from an OK edelbrock 4bbl set up with what felt like a decent tune and standard advance curve to some spot-on tuned weber carbs with 15 initial and a total of 28* saw my temperature at speed drop by 1/3rd.

I'm now a great believer that many overheat, or in my case just running hotter than expected, issues are timing, tune and distribution related after that experiance.

to me it sounds like the throttle position in the speed range quoted results in a mixture that is marginal and slow burning, and that fire is till rageing as it exhausts down the headers..
Under hood area gets very very hot, very quickly at a specific point in the rev range when you are crusing at speed, and already have max air flow through the radiator.

timing and mixture (content or distribution) related

Plugs mentioned above as well yeah could be... poor flame front, slow burn slow igntion is what i'm talking about. wrong heat range plays havoc.

just my view from my desk at work... perfectly happy to be wrong.... :)

Dave