Generally the fan doesnt make a difference at speed, its the air flow through the radiator that takes care of the cooling on the highway above 40 mph. The fan is for stop and go traffic to mimic the air flow at speed. What you arent considering is that above a certain RPM your engine is loosing efficiency and is creating more heat....the harder you drive it the hotter it gets. Your car temps sounds normal for its temperature and being at 210 isnt out of the normal operating range. If it cools down as you slow down then you are okay. my car does the exact same thing on very hot days when I get off the highway onto side roads. on any day below 90 its happy as a clam


Those high RPMs are your issue and you should consider a 5 speed swap if you are going to speend that kind of time on the road. I have a 5 speed with 4.11 rear gears and I am just under 3000 rpm at 80 or 85 mph...forget exactly....its a great investment

 

And you cant compare a cold days cooling readings with a hot days cooling reading, the ambient temperature will take away more heat quicker on cold days.....my car will stay at or below 180 on days in the 70s so I would say you are just experiencing the heat of the work you engine has to do at sustained high RPM.

 

So is the spring intact in the lower radiator hose, or not? We still don't have a straight answer.

If the spring isn't rigid along the length of the hose (easy to check, cold, with your hand), it needs to be replaced, and is 100% your problem.

And please confirm your temps with an IR temp gun. You may be surprised.

 

I said in post 16 that lower hose is correct and functioning beautifully. By correct I mean OEM replacement hose w/correct spring properly installed and verified to be functioning correctly. I have a close friend whose a retired mechanic w/a garage full of cool cars and most of his tools still and we've gone over this car front to back top to bottom and I wouldn't hesitate to drive her cross country right now worry free. So I assure you I'm aware of the colapsing lower hose on these cars and we made damn sure to get that correct. I really do not have a cooling problem, I was only posting this to inform those like me with perfectly functioning cooling system yr round and the only temps above 200 are on 90 degree days at high speed for more than 15 miles where the temp stays at 220 plus but doesn't overheaat, that a stiffer fan action keeps the temp right on the money even on 100 degree days at high speed for 15 or more miles even w/AC on. If I find a fan clutch that functions smooth and quiet yr round but really tightens up at 220 plus and keeps the 100 degree hwy temp at 200-210 I'll pay whatever they're asking for it. I will get a temp gun one day but since I don't have a temp problem it hasn't been a priority. I'm aware that a 220 reading on the factory gauge is hit or miss and could be 10 degrees or more in either direction. From a lifetime of older cars I can tell this car runs nice and cool and smooth whatever the exact temp is

 

No sarcasm but luckily science was my favorite subject in school so I get that cooler air means more efficient heat exchange and of course cars run cooler in winter than summer. I also comprehend air flow so I'm aware of the dynamics the clutch fan employs to bring air in when stuck in summer traffic On this particular car the lack off air flow is well documented so I paid very close attention to sealing up the air box and making sure nothing was impeeding air flow to the radiator or alowing it to run around. I even plugged a couple spots I felt were over looked.

Mine runs cooler around town in the winter of course. But on the hwy at 85 mph she runs 200 yr round even on a 40 or 50 degree day. The only time it deviates is this time of yr and even then only above 90. If it's 88 out she'll lay right on 200 or a tad higher which is perfect as these motors are made to run best between 200 and 210. I notice on my 2011 Camaro SS that this time of yr she runs 206 to 208 and the fans kick up often so I agree that 200 to 210 is no worry and actually where you want it. I chuckle when people post worried about 200.

I would argue air flow but if that were true wouldn't the car always be a little warm at 85mph regardless of air temp? One thing I do know is that a stiffer fan action on hot days makes her run perfectly cool on the hottest day ever. I of course don't want or need a stiff fan 24/7 but I'm convinced that stiffer action maintains a proper temp under heavy heat load. Now whether that's the most efficient way or the intended design or not I have no idea. But I posted earlier that if there is a clutch that operates quiet and efficient and kicks in stronger under abusive conditions and keeps the temp steady in the sweet spot then I'll take it

 

OK, my perspective here. I live in tropical Queensland Australia. It's Bloody hot here! When I first moved over here. I quickly learnt I had the exact same issue you are describing.
I installed a Champion aluminium radiator. It helped a little, I went over every gap around and over the radiator. Plugged off every path air could possibly find around the radiator. It helped a little. I tried a high flow thermostat. It helped a tad. I tried various timing settings, mostly finding the vacuum advance timing had the most effect on high speed hot outside running temps.
But. Still, when outside temps were below approximately 94 degrees, no issues whatsoever. But when temps got higher. There I was chewing my finger nails off watching the temp gauge!
In went a 4 row aluminium rad meant for a big block car. C5 electric fans with there built in shroud.
The fans NEVER run on the highway now, never.
105 degrees F outside, Fans only kick on at a long light or crawling slowly in extreme traffic.
Big! Kickass rad, proper shroud that flows when your moving!
No more issues. And I did fight this for several years.
Bottom line. NO, THE STOCK RADIATOR IS NOT GOOD ENOUGH!!

 

Thanks for confirming that unambiguously!

 

It's challenging to post w/o giving so much detail that it becomes too much to read to get to a point. But mulltiple posters mentioned lower hose so I was clarifying my situation I appreciate all feedback as I will be driving this machine 'till I die so I'm always open to learn or share info that'll keep 'em rolling down the road.

 

I'm gonna go your route when I drop my big block in her, but for now the stock system is fine. I'm gonna need tons of advice on that project, particularly fellow 77 4speed owners!

 

I have a couple of suggestions for you now and for when you install that big block.
Air flow at speed and engine compartment temperature is always a concern with these cars.
Chevrolet noticed they had temperature problems on their ac equipped cars and they added a bolt on factory lower air dam extension to all the big block ac cars.
Adding one will pick up and force more air up into the radiator.
On my 73 bb, I removed the front license plate and mounting bracket, replaced it with an oem center grille which basically allowed for 33% more air flow through the front grills.
Swapping out the oem style radiator and going with a better aluminum aftermarket radiator with make a huge difference in keeping the engine temperature cooler during high demands.
DeWitts and Champion seem to be the most popular and show the best results.
Running an Edelbrock performance hi flow water pump is a plus and adding a hi flow thermostat will allow more coolant to flow through the system.
If you are or plan to run headers, make sure they are ceramic coated.
Add some type of venting which allows the extremely hot air to pass through and escape from the engine compartment.
Adding vents in the hood allows the heat to escape and the proper vents and their placement will allow more outside air to be pulled into the engine bay and through the radiator.
These cars allow little air through the radiator and when you start running them at higher rpm, the engine temps will run hotter than normal.
On my 73, my rpm’s were 3100 at 65 mph with 3.36 rear end gearing.
If I kept it at 60 mph my engine temps would run around 200, anything faster and the engine temp would increase to about 220.
On the California highways, I was getting run over.
As suggested above, if you want to run at 80+ mph then swap to a five or six speed transmission and keep the rpm’s at a minimum.
Cooling a big block in these cars is only done by taking every step possible to make it happen.
The problem is the design of the body allows very little air through the radiator so you need to do everything possible to get more air to pass through, you’ll need to improve the cooling system to keep engine temps down and allow as much of the hot air to escape the engine compartment.
One other thing to keep in mind, when your car was built, the maximum speed on highways was 55 mph, so that is the speed your car was designed to run the most efficient.

 

[QUOTE=OldCarBum;1608061025]I have a couple of suggestions for you now and for when you install that big block.
Air flow at speed and engine compartment temperature is always a concern with these cars.
Chevrolet noticed they had temperature problems on their ac equipped cars and they added a bolt on factory lower air dam extension to all the big block ac cars.
Adding one will pick up and force more air up into the radiator.


I will definitely go w/the Dewitts when I land the BB. If I had the money I would've already done it but mine runs perfectly cool at 80 or 90mph yr round and only creeps up on 90+ degree days and even then doesn't overheat so I drive the hell outta her even on 100 degree days like I did today driving the 50 mile hwy round trip to work and back. So air flow is not a big prob w/the stock 350. I would love a bigger air dam that is plug and play. If I could find an in stock pace car one that supposedly will bolt right up on a 77 I'd buy it in a heartbeat. Again though I don't need it now but I wiil later. Actually after all the studying I did about these cars before purchasing this one, coupled w/my personal experience w/the 75 Stingray I owned 25 yrs ago, I'm very happy w/the engine temps in this one as well as the lack of interior heat. The 75 woukd bake you like a clam on a 40 degree day w/t-tops off. This one has no noticable cabin heat even after driving 250 miles at 80 plus. If I were gonna keep this engine I'd be happy as is. Again the only reson I started this thread was to say oh by the way a stiffer fan action will scrub that excess heat perfectly and she'll sit on 200 all day at hwy speen in the baking heat. When I drove to work at 100 degrees she ran barely a needle width above 200 and on the way home this evening still 90 degrees (at 10pm) she stayed a needle width below 200 and I was burning across the 7 mile long bay bridge keeping pace w/the 85 to 90mph traffic. I wouldn't mind the center grill piece either although I'm strangely ok w/the front plate

 

Air flow on the highway.
77 - 79 front spoiler extension part of Heavy duty cooling option in those years. It's made out of conveyor belt kinda reinforced rubber. These really do help scoop some air through the radiator. Although getting hard to find nowadays. If you google it I have found a couple out there.
A couple pictures of my car in the garage just now. Hard to get a good picture under there. But here ya go.



I don't think the original retainers are available at all anymore. I've added extra rivets to mine over the years anyway due to abuse. Might not be super pretty but doesn't break on every driveway and speed bump. And it does really help.

 

Mines a 77 to be clear. And the heavy duty cooling option probably wasn't all that popular in these years. I really don't know for certain. I do know it really helps pull in air on the highway.
And it doesn't break left, right and center!
And it fits right on your car!
(OK you will need to drill holes, come up with rivets and reinforcement plates).

 

I know I suck at photos, so, from the 77 AIM.

As you can see, a factory option. It bolts right onto your 77.

 

Thank you! I've seen home made ones that look ok but I'd be thrilled to find on of these

 

There out there but getting hard to find. I think I seen a guy in the UK with one. Ya have ta do some goggle searching around. I like mine not because it's super pretty, but rather because it actually makes a difference and it doesn't break on every pot hole, speed bump and steep driveway. It really does get hot here. When the outside temps go up you need even more air through the radiator.