I have a 472 hemi in a 67 R/T that runs cool in hot weather in traffic and down the road for what I say are short high speed runs. At 65 to 70 mph the temp will rise over 200 (slowly) if kept at the speed. Slow to 50-55 and the temp will go down. Alum rad with stock waterpump. I'm thinking a problem "could" be the lower hose collapsing at higher RPM. Does anyone use a non stock rigid or flex metal lower hose ?

Is there a chance that this might be a carb tuning issue when the primary circuit transitions in?

I recently asked a local parts store why the newer lower hoses did not come with a wire. They said that the manufacturers are using better rubber materials that no longer require the wire insert which prevents collapse.
How old is your lower hose?

Here is what we purchased for both our big block cars. It's for a Ford hose but it works just fine.

https://www.cjponyparts.com/lower-radiat...5-1973/p/HW769/

You may need more radiator

Problem could also be the coolant isn't spending enough time in the radiator due to the thermostat being too low a temp setting.

That's an old wives tale.

Oh, OK. Never mind, then.

Overheating at highway speed is a sign that you're either not getting enough air flow...like electric fans blocking the radiator...or the radiator is too small. Another possibility is that someone accidentally used 100% antifreeze instead of 50/50

I believe a couple responses are taken out of order

the coil spring inside the lower hose is an aid on the assembly line where the cooling system is filled under vacuum

& if your cooling system is developing proper pressure, the hose is not going to collapse

if you can't maintain temperature & it is exceeding your thermostat rating - the excellent flow & open thermostat may not allow the fluid to spend enough time in the radiator to cool

you do not mention what fan or shroud you are using.

I agree, if it can keep up in town, air restrictions are hurting you on the freeway.

The fact it is coming back down at 55 tells me you have enough radiator and it is spending enough time there.

Something is blocking air flow.

It might still be possible that your lower hose is collapsing, and you could test that by staying in a lower gear at 55 so your rpm is higher.
if it starts creeping up, then I would use the steel hose with the rubber ends.
http://www.jegs.com/i/JEGS/555/511241/10...DYaAl-yEALw_wcB

mechanical fan with schroud...no blockage. Now....IF the engine is working harder at high speed, it may be generating too much heat for the Alum rad I have in now. The motor has a nice cam/stroked and stock bore. It's also a waterblock. It's got to be the hose or rad and the hose is easier and cheaper to try.Thanks to all. (the coolant is newer and 50/50)(stat is not a player unless not opening and it opens)

You might be able to coil a welding rod in the hose to confirm/elim that potential without any expenditure. Post what it ends up being. EDIT with more thought, you could (in your driveway) run it up to the RPM that it is acting up at on the highway & see if the hose starts to suck shut. water flow is the same at a given RPM so it it is doing it at speed it will do it in your driveway at rest. this will quickly resolve that potential.

Are you running a hood to radiator support seal?

Is it an aftermarket radiator. Many of the aluminum radiators don’t seal well on the slides to the radiator support. So air spills right around the radiator.

The shroud could actually act as a limiter when too much air tries to enter through the radiator.
Some shrouds have rubber flaps that open up when enough airflow is there.

Also most likely that underhood air can't escape the engine bay fast enough causing lower airflow through the radiator and engine heat is building up.

A front spoiler can create some lower pressure behind it which could in turn help evacuate hot underhood air and aid overal cooling.

I don't see the shroud as suggested is an issue at high speed

Had that with bad head gaskets

not having any coolant issues or performance

Performance, car would run fine until up to 65-70MPH and the temp would climb but ran fine at slower speeds. Head gaskets were bad

Don't rule out air backing up under the hood at high speeds just yet.
One way to make sure/rule out is to install mbar manometers in front and rear of radiator support and run lines into the cabin to view them.

Unlikely, but headgasket issues would also show up after shutting the engine off and restarting it shortly after when coolant pressure is injecting coolant into a cylinder. But it's more likely engine combustion pressure is making its way into the cooling system when the engine is running hard.
Hard radiator hoses would be a result of that until pressure drops again.

Where's your timing at at higher speeds?
Fast/Slow curve?
Vacuum advance hooked up?
Late timing will cause warmer running engine.

so then, why when a car is running hot, do you " race" the engine, thereby speeding up flow? wouldn't you want it to idle, so the coolant spends more time in the radiator?

what's your timing?
what carb?

see thread in the race section. "time in the radiator" is an old wives tale. you need coolant flow, air flow, plus adequate radiator size to maintain cooling parameters.

Watching this thread as I have the same issues with our big blocks.

People saying YES thermostats 50%, people saying NO thermostat %15 and people saying cut the guts out of the stat %35 .

We have run with the guts cut out, too hot and just run without a thermostat and still too hot, trying the 180 thermostat soon even though some say it will not help.

Holley 950 double pump

12 at idle..36 at high speed

car runs strong to 130+ but heats up like first stated

terzmo, Is your timing ALL in at 65mph ? Maybe it is not full advance at the RPM your sitting on ?

Anyone know if those super coolants or water wetters work at all? I went with a larger radiator, no issues under any conditions.

This is one of my 3 most favorite myths though. Neat thing about it is that it will NEVER go away.