I seem to have a problem with my car running above thermostat temp ( 195 ) when I cruise at highway speed. 55 mph and 2900rpm it runs up to 210. It may even go higher but I don't push it .As soon as I drop down to lower speeds ( and rpms ) temp drops back to proper range. Coolant is fresh, I have a stock shroud , fan maybe a bit deep in the shroud ( more of fan is in it than out ) 3 row radiator and timing is set properly. Could it be a water pump whose impeller can't cope with the RPMS. It's the only part that's suspect , it doesn't leak but I've seen impellers that have coroded, therefore they don't push as much water. I have a post about not getting coolant surge into the recovery bottle when hot, could this be an indicator towards the problem?

Are you sure the radiator is full. If you just flushed the system, it is possible you still have air trapped in the engine. Check the fluid level in the radiator after you drive (and the engine cools down) and top off as required. Once the radiator is completely full of fluid, you should start getting overflow in the bottle.

I have/had a similar problem, but when I exceed 65 mph (no tach at the moment, but sounds close to the same RPM range as yours) the radiator starts spitting fluid out the overflow. I put a temp overflow bottle on, but it would still puke... that didn't fix the 'problem', just the result.
I figured maybe the radiator was undersized so upon completion of my resto, I'de go with a better radiator plus switch to an electric fan. My water pump is new.

But then.... as I dismantled the engine chasing a bad valve, when I took off the heads... someone got a little crazy with the silicone on the head gaskets and probably 40% of the water jackets were clogged with rubber gasket crap.
I don't know if that was my problem or not, but I'm darn sure glad I found it.

Just wanted to throw that out in case you've had any work done recently... hope this helps.

Is it a stock fan? Is it something that just started to happen or has it been happening for a long time?

Is there a spring in the lower rad. hose?

do you have a fan shroud,and something that helped me,before i Really fixed my cruising temp problem,with a Large Griffen Alum radiator;
I added a lower front,spoiler that helped as much as anything else at cruising speeds..
I have a flowkooler waterpump,and a highflow t/stat,180 deg,that i put on the engine when i added the Edelbrock Performer cam/intake setup.
WIth the extra power,i knew i would have more heat,and,until i added the Large Griffen,i would see up to 220 at 70 mph extended cruise,{like driving back from Carlisle,in 85 deg temps}
Now with the griffen,i see 200 on the same type run,
Oh my plugs are very light colored after a run like that,not white,but not Brown,like a tan...
I am running a junkyard HEI,and a Holley 850 dp,with 4 corner idle,and the engine is stock compression, {10.25}
graemlins/beers.gif

Fan doesn't matter at highway speeds; 90% of the time, your symptoms point to either a collapsing lower radiator hose or a radiator that won't cut it any more due to internal scale/corrosion, regardless of how it "looks". graemlins/thumbsup.gif

To support JohnZ's suggestion, if lower hose is collapsing, this is due to waterpump sucking the hose dry, not enough flow from the radiator, due to being restricted or too small, or too small of a thermostat opening.

The lower hose spring suggestion is a good one, and certainly a corroded radiator would not help either, but if you have been fooling around with the carb (tooooooo lean jets) or intake leak!

Nearly all the cars that I have fixed with this problem were ALL lean if freshly installed or assembled or changed. The faster the car went the worse the problem became.

The pump could be an issue, and certainly if the coolant was low too. The overflow will only work if the system is totally full!

Check it out and report back!

I have considered the lean condition. I thought that reading the plugs, essentially having to pull over and yank them while it's piping hot would give me a decent read on what my cylinder conditions are like at that moment.
The lower hose is an old Atlas model from my days of working in an Exxon station, back when kids pumped gas for customers. Although I suppose in NJ, that's the only way you get gas. It's old, I will replace. It's the universal corregated type, so I'm thinking it may not even have the support wire/spring in it. Thanks for the ideas!