Check out this expose' from Coolcraft.com for understanding how and how not cool your engine with a radiator:

Radiator Core Styles
What core type is best suited for your application?
Aluminum or Copper/Brass?
Do you need a new radiator?

Core Types:

The radiators that Cool Craft Components sell come in 3 different base core designs along with add-on options to offer the most comprehensive line of drop-in replacement radiators on the market.


1. Standard Automotive Core [OEM style core design]
2. High Efficiency Core [Available in Copper/Brass or Aluminum]
3. Optima Core [The best cooling core on the market]
4. Triple flow Option [Add up-to 15 degree additional temperature drop to any of our radiators]

Standard Automotive Core:



Similar to the OEM style radiator of the 60's its constructed using 1/2" fins and is available in 2, 3 or 4 rows. If you are looking for the same cooling as found in your original 50's - 70's car, then this is core for you.

High Efficiency Core:



Our High Efficiency core is available in copper/brass or aluminum construction. The copper/brass High Efficiency cores are available with 2, 3 or 4 rows of 1/2" tubes. The aluminum High Efficiency core is available with 2 rows of 1" tubes. Our 4 row copper/brass and 2 row aluminum cores cool the same with a slight edge going to the copper/brass core. How is this possible? Its simple. The 4 row copper/brass core is constructed with 1/2" in-line tubes giving you 2 inch thick core. The 2 row aluminum core is constructed with 1" tubes, again giving you a 2 inch think core. Both cores use similar size serpentine fins giving you similar amounts of heat transfer points. For more information on the cooling efficiency of aluminum vs. copper/brass cores, please refer to "Aluminum or Copper/Brass" section.

Optima Core:



For most applications, we suggest using a Standard Automotive core or a High Efficiency core in either Copper/Brass or Aluminum. There are some of you horsepower junkies out there that have blown their engines and need the cooling power of our Optima core. Constructed using an in-line tube design with 1/4" serpentine fins we are able to put more tubes in the core which increases the amount of heat transfer points. Our 4 row Optima core has as many rows as a 6 row Standard Automotive core. Couple this core type with the Triple flow add-on option and you will get the greatest temperature reduction from inlet to outlet in a drop-in replacement radiator available.

Triple flow Option:



Our Triple flow option is an inexpensive way to add up-to 15 degrees more temperature drop from inlet to outlet to any of our radiators. By building internal walls into the tanks, the coolant is re-routed to pass through the radiator three times (top to bottom or side to side) resulting in three separate exposures to temperature dropping airflow, with little to no adverse flow restriction.

Triple flow Option NOTE: Due to the internal walls we are unable to include a transmission cooler in radiators ordered with the Triple flow option. We do offer auxiliary coolers that look and work great. This option is not available for flathead (4 connection) radiators and requires that the inlet and outlet are located on opposite sides.


Aluminum or Copper:

The thermal conductivity or heat transfer rate of copper is 92% versus aluminum which is approximately 49%. However, the copper fin bonded to the tubes, or water passages, using lead solder is very inefficient and slows the heat transfer rate to just slightly better than that of aluminum. This can be a disadvantage of copper if the bonding process does not allow the copper fin to touch the brass tube, and why not all copper/brass cores of similar design, but different manufactures, transfer heat equally. Copper/brass radiators, because of their weight and durability, have been around a long time and can be easily disassembled and reassembled for cleaning purposes.

Not the case with aluminum, unless speaking of the O.E. version that comes with crimp mounted plastic tanks. As a result the life expectancy of the aftermarket aluminum radiators will be far less than that of copper/brass. To better understand the function and performance of any given radiator it helps to understand the “cooling” process and think of it in a way that allows for comparison. The words cooling, or better cooling, or efficient cooling are thrown around a lot in advertising and promotional terms but for the most part un-quantifiable at best without a reference or yardstick to measure by. To measure and control the cooling processes you have to take several variables into consideration.

Variables include engine temperature production at different rpm’s, or engine operating btu output, coolant absorption rates, coolant flow rates, or gpm’s, and coolant temperature reduction rates that will vary with the size of the radiator and the amount of (cfm’s), speed, and temperature of the air flowing through the radiator. The only device to actually compare one radiator vs. another with absolute control is to have a wind-tunnel that can duplicate actual driving conditions under various specified conditions. U.S. Radiator built radiator dyno or test stand in 1999 and tested every core design and manufacture, in both copper/brass and aluminum, for plain and simple temperature drop, inlet to outlet, at specific and controlled parameters.

So what did US Radiator learn? First and foremost, they discovered that where the radiator is concerned core design and NOT material had the greatest effect on temperature drop. While all radiator cores might look the same they perform differently based on tube spacing and fins per inch. Heat transfer points where temperature is actually allowed to leave the radiator are where the fin is bonded to the tube. The more transfer points, the greater the temperature drop. A 60’s core for example had a 1/2” tube spacing (ie, 1/2” fin between the tubes) and by going from a two row radiator to a four row core design they were able to double the heat transfer points which resulted in a 15-20% increase in temperature drop without changing the other variables (air flow, coolant flow).

In the 80's the Japanese came out with a core design in response to the need to downsize, which has become the standard, and was efficient enough to allow the re-introduction of aluminum (a less efficient heat transfer material) at the O.E. level. By changing the tube spacing to 3/8", a design referred to as High Efficiency in the industry, more tubes or water passages and fins were allowed across the face of a core with a specific width in inches. The design was simple enough but proved to be very efficient in that more heat transfer points created greater temperature drop inlet to outlet. At this point the move to aluminum construction was purely financial in that raw materials are purchased “by the pound” and a finished aluminum radiator weighs about 25% of a copper/brass unit (dollars per pound being almost equal at that time) and resulted in huge savings to the O.E.’s . This is why we've seen most copper/brass manufactures either switch to aluminum or fold up their tents permanently.

It is important to note that this decision was based solely on financial savings and should not be confused with more efficient. In fact the tests that US Radiator conducted, resulted in almost exact temperature drops, aluminum vs. copper/brass, at all operating ranges where the core design was the same with a slight advantage going to the copper/brass unit (even against their own aluminum units).


Do you need a new radiator?

Lets face it, radiators are expensive. Its in your best interest to exhaust every option before investing in a new radiator, unless of course your existing radiator has obvious damage or is older than dirt. There are many reason why a car may be overheating. Some are auto make/model specific which won't be covered here. The web is a great resource to turn to to find out what others have done to cure their overheating autos. Its probably not a stretch to say that most automotive magazines have tech articles on cooling in their spring issues every year.

Airflow, let me say it again, AIRFLOW, or lack-there-of, is one of the major contributors to overheating problems. Lack of airflow can be a result of an un-shrouded radiator, fan installed backwards (rotating in the wrong direction) or a manual fan not sitting at the proper angle in the shroud. We highly recommend a shroud properly fitted to the fan and radiator. The only time you really depend on a fan is at idle or low speed where there is little or no air flowing through the grille. Shrouds are necessary to maximize the amount of ambient air being pulled through the grille and radiator. Proper fan and shroud alignment should be leading edge 1/3 in and trailing edge of fan 2/3 out. The air flow off the back of the fan deflects at about a 45 degree angle when set this way. When the blade extends further into the shroud the air off the back of the blade flows straight back into the block and decreases the airflow efficiency by about 15%.

If an electrical fan is the only way to go then by all means place it on a shroud that covers the entire core. We often see an electric fan attached directly to the core and the only thing this does is waste the rest of the core surface when you need it the most. A 16” electric fan attached to a core only cools a 16” circular section of that core. Where space is an issue we offer 3/4" deep custom aluminum shroud that enables adequate air flow over the entire core and when combined with a thin-line electric fan results in a total depth of 2 3/4 “.

 

Since this happens at highway speeds, I don't think it is your fan clutch. You haven't told us much about your radiator. Is it new or recently overhauled? You really do need a thermostat.

 

You may want to check or replace your EGR valve. If it isn't functioning properly you could be running hot when running at highway speed.

 

Generally speaking, at freeway speeds you should have sufficient air flow across radiator. And it's a high load condition (vs. stop and go). Suspect radiator efficiency. I am not sure why people remove their thermostat. Just about every car came from the factory with one. Inspect all components; you have a cooling system. Heck my 68 L36 never runs hot and it has pretty much stock parts, including the original (recored) Harrison radiator.

 

Thank you for all the advice. I guess my first task is to install a 180 degree thermostat. Next will be to check the radiator for blockage. Then on to the timing. I think the timing is a little advanced given the occasional dieseling when hot. I'll post to let you know how it goes.

 

I had about the same issue when I tried to run no shroud.

 

Did you have any luck?

 

Couple trouble shooting hints that need to be investigated. Heat on high and fan blowing max if she starts overheating, the heater coil will act like a secondary radiator and will get you to safety, but that doesn't fix the issue.
First, (engine cold), verify the radiator has no restriction. Shine a flashlight down the filler neck and you should see the cores (veins). Antifreeze has clarity so you would be able to see a half dozen or more cores. Old radiators will have a slight thin white residual material which is normal on the entry of the cores but not like toothpaste, and it should not be milky to your antifreeze - if so, you will need a cleaning and pressure test. Second, since you are in the cooling system, check the hoses, squeeze test, they need to feel like they won't form a fold .. Bottom hose is different, it has a support coil built inside, so those need to be inspected at the clamps. Ballooning is not good, collapsed lower hose are more difficult to view if it is distorted in any way I would suggest in a new one along with clamps. Belt tension and fan clutch needs checking. Fan clutch basically will sound noisy and you will hear if the fan is overworking itself creating air drag.
One last suggestion would be the turbine slipping on the water pump internally. I have read in Corvette Fever Tech tips on a problem they have with water pump shaft that would slip spinning the turbine thus not quite cooling like it use to. But overall, keep your cool. Stay thirsty my friend.

 

My `76 consistently runs 200-205 when it's warmed up. The car is stock aside from a 300 horse crate engine that was new when I bought the car 4 years ago. The temp will sometimes hit the 210 mark if I have the AC on in traffic and it's a hot day. The only mod to the cooling system is I put a pair of ball valves in the heater hoses so I can run with no coolant going through the heater core. I have never had to add fluid to the rad.

 

#1 if the system is working properly, your car will run at same temp. on freeway as in city.
that temp. is determined by the Thermostat, i suggest 185.

When I assembled my BB motor with pretty much new componets and orginal good radiator,
the first week or so I fought with higher city temp. than freeway.

Final Resolution... Air Lock,... it is very difficult to get all the air out of a Corvette system,
mostly due to the motor sitting higher than the radiator.
I must have tried 10 other ways of completely filling system.

the way I resolved .... removed the radiator hose to thermostat connection at the radiator side.
stick a garden hose in the radiator, keep it running, start car, warm up enough for the thermostat to open keep running,
keep the hose straight up, shut off car fill hose completely while holding upright, then quickly reconnect to radiadtor.
Once this was done the car stays rock solid on 185.
Caution this will create hot water coming out of the Motor radiator hose!

 

Thanks for all of the tips. Once I can free up some time, I'll get to trying out some of the advice given.

 

i just drill a couple small holes in the flange of the thermostat, that lets the air pocket flow through . then you just top it off after its run for a couple minuets . and now some know it all will chime in with the car won't come up to temperature or some such nonsense.

 

this will not get prevent air lock, or cure it. my T-stat Already had holes drilled,
it will help miniminze, and I do agree with drilling the holes.
like I said, i drained and refilled many times, thinking, ok now I have all the air out.
...I was wrong. .... several times. find a way to ensure you have all Air out of system.

 

I would be willing to bet the problem is your radiator is internally plugged/corroded.. I went thru the exact same issues, I even had my original 4 core radiator rodded out and boiled clean and it still ran 200*+ on the highway within 20 miles... I did ALL of the suggested tricks... Could never get it stable at 200-210* hwy temps..

I put a Dewitt's aluminum radiator in with the stock 7 blade fan, shroud and severe duty clutch, temps dropped to 170* instantly on a 90* day on the highway. Basically 30* drop in temps on the highway.

I now run 180-185* all day with a 650hp, iron headed big block with AC blasting.


Go buy a Dewitt's, slap it in, seal up the core support and shroud well.. Put a Hayden Severe duty can clutch on it.. That thing will run cool as can be on the highway.. I'd put a 160* thermostat with the bypass hole (or drill a hole).. You'll be good to go.

 

You mentioned you have the radiator seals in place. Do you have this one? (Outlined in red arrows.) Note the mark it makes from contacting the hood (Yellow arrows.)

 

Well, I finally took a closer look at the interior of my radiator. Initially saw that the radiator water was flowing, but at a closer look, it appears that some of the tubes are not flowing very well. It looks like a new radiator will be my next purchase. Now, what does the forum recommend as a low cost aluminum radiator. I'm leaning toward Champion due to cost. Anyone have any experience with a Champion radiator? DeWitts are just too expensive for me.

 

Check out what is available at your local radiator shop...you may be surprised what you can find. I did and found an aluminum with 3/4 inch tubes (2 row). It works great, affordable, and keeping money in community of local businesses.

 

Asian, if you weren't so darn far away I'd give you an aluminum radiator I have just to get it out of my garage. Anyone near San Antonio need a radiator?

 

I run a constant 165-175 no matter if it's 100 degrees out or 50 degrees out. Freeway or city driving doesn't affect it.

 

i have a champion and it works very well I've had zero issues.
when i bought it the people who sold it to me said to expect to find the box has been opened, because we take them all out and inspect pressure test and re package each of them. when i got it there was no damage.