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Radiator CFM?



My car is still overheating and the engine has been rebuilt. I have the stock fan/clutch setup. I bought two electric fans for the car and chose to go with the regular fan and setup and auxillary fan. The vehicle is still overheating with the stock fan and i am opting to put in the two electric fans. I can fit 2 12" fans across the radiator of the car the problem is that they pull about 600 cfm each. The total is 1200 cfm. I have seen a dual fan setup from Be Cool that can pull 2100 cfm. Other than the cfm difference the price difference is also significant. about $170

My question is

What is the necessary cfm to pull across the radiator to keep it cool. The radiator is a 4 core (i am not to sure what the fins per inch are).

In desparate need of some technical help, SSCAM69

again the engine has been rebuilt, new cap, rotar, pump, radiator, thermostat, etc etc.

I would go with the one large fan vs. the two smaller ones. I would think you could run the electric only.

Refresh my memory, when does it overheat? Has it always, or did it just start after the replacement engine?
The reason i took the engine to get rebuilt was the fact that the engine was overheating. So i have spent 2k and it is still overheating! I took her out this morning and she overheated on the freeway.

A friend suggested that i get a better fan with more blades on it. I cannot feel the air flowing behind the actual blades of the stock fan, only between the shroud and the edge of the blade of the fan.
If you have the original catalytic converter it could be clogged and causing the overheating also if you have the original exhaust rams there is a lever on the ram that sometime will stick and cause the engine to run hot.. Just a few .02.
So you get hot at speed. Do you have a thermostat in the engine?

Did you say the radiator is a new one?

Is your timing advance working proper?

When you say it runs hot, how hot? Does it steam over, or just too hot for comfort?

Do you still have the little front spoiler lip under the nose?

What pound rating radiator cap are you using?

Do you still have the fan shroud?
What about the foam around the radiator frame. I heard that the foam is important to the radiator flowing air thru it.
I have a alum Griffin rad and it never runs hot. Also have a one piece molded nylon Flex fan which is light weight and gets the job done. I run a 180 deg thermostat and the needle sits right on 180 all the time.
In response to Chris

Yes it has a thermostat, 180 deg

The radiator is relatively new, it was barely used but sat for about 2 yrs, has been cleaned out.

Timing has been set and is o.k.

not hot for comfort, the gauge was reading 220 and climbing

I have the front spoiler on the nose

I believe its 15 lbs, not to sure

Yes, i have the shroud, the previous owner melted the sides. For what i have no idea and have been trying to figure it out. I patched it up the best that i could to form a seal around the radiator.

In response to resto75

I bought the seal kit, but have not yet put the pieces that go between the hood and the radiator frame.

New developements:

I mentioned that the air could only be felt moving in the area between the shroud and the edge of the blades, you could not feel the air passing through actual fan. We took the fan off and found out that the blades were cut to make them shorter and some of the blades, after taking a closer loo, had no curvature. I am going to try and buy a rigid flex type fan to replace the old one. I am hoping this will do it.

Thanx again for the help

I bet I know what happened.

The prior owner broke a motor mount. Somewhere along the way also nailed the throttle and torqued the engine into the fan shroud--this broke the shroud on the side and tore up the blades.

Then, Bubba came over and offered to patch it up for cheap.

I actually did the shroud deed on my 74. Right after putting the engine back in, I had the hood off and was hot dogging in front of some friends (back in high school). I failed to replace the motor mounts (what do you expect for working part time at Kentucky Fried Chicken and going to school?). I dumped the clutch at about 4,000 RPM and all of a sudden--WHACK-thump, clang clang clang.

I think I told my dad that I had left a wrench in the shoud that got caught by the fan. Anyway, we first tried to bend the fan back, but it was too messed up. :r
Chris how does the air flow through your car. Like i mentioned earlier i can only feel the air flowing between the edge of the shroud and edge of the fan blade. I cannot feel it directly behind the blade, kinda a dead area.

Is yours the same for that matter?

Is this case similar to anybody elses?

I have tried 3 different blades and they all perform the same.

The car still overheats especially at idle.

Do you feel the air directly behind the blades?
Does the shroud need and extension?
What was the open flap for in the shroud for the L-82?

couple more questions, are you using a new fan clutch or the old one? What brand? I know for most of the GM V8's Imperial ( a common brand) has two parts a regular and a heavy duty. the two part #'s were something like 215149 for the regular and 215045 for the heavy duty (or something liek that) It makes a huge difference! The regular sucks :booty !! You definitely need the heavy duty. If you are running a fan clutch then don't get a flex fan, get a fan clutch fan. I'm sure you already know this, but I'm just going by what one of your earlier posts said. If you use a flex fan then you should take off the clutch and put a spacer in it's spot. And one last question, is the fan all the way, or at least mostly inside the fan shroud?
I hope you get this taken care of, I know how much it can suck.
One last thing, have you checked to make sure the car isn't running lean which can also cause it to run hot??

Good Luck,

Yes the fan clutch is brand new, i am not to sure what brand.

All the fans that have been tried have been rigid fans. The fan is almost all the way in the shroud.

The mechanic had and Imperial fan from autozone, the thing measured 18". it was to big and would hit the shroud on the lower end. So i went back to autozone to buy a 17" to fit in the shroud. Low and behold the guy said that the car used and 18 or a 19" fan he turned the computer screen and showed me to my disbelief. The pully is offset from the center of the shroud. Is this normal?
That seems odd, it seems to me that the fan should be centered and not have much clearance between the fan and the shroud with even clearance all of the way around. I wouldn't think more than a 1/2" of clearance at any point, maybe 3/4".

Yeah we were scratching our heads for awhile ourselves. I am getting really tired of this. After 3 different fans that have been put on the car and it still has not solved the problem. The closest we got was 210 cruising temp on the freeway, but when at a light climbed a bit past 220. Did not let it go past that.

I think i am just going to install flex-a-lite dual electric fans. They are rated at 2500 cfm which should be sufficient for the car. Thats if there is not improvement tommorow.
I was trying to find the Imperial website to see if they had an online catalog, but found the autozone site has an online catalog. Checking either the 18" or 19 " fan gives different than average V-8 part numbers, so I'm sure the correct fan clutch is heavier duty than normal.
I'm on this forum because my dad has a vette, but the last time I had V-8 American Iron, '70 Skylark 350, I used the heavy duty fan clutch. My engine would get up to about 230 cruising at around 4000 rpm on the highway in FL, then the fan clutch would kick in. It sounded like someone just started up a turbine jet engine under the hood, the temp would drop to about 200, and then it would go back up. The last car I had I mid '80s low hp Olds boat w/ Olds 307 I could feel the fan kick on and off, so they definitely draw some power.
I would go with the electric fans in an instant, just make sure you run them on a thermostat rather than all of the time, and make sure your alternater is up to the job. If the amperage isn't high enough it's really easy to get a higher amp alt for most any GM car.
Good luck and I hope you get it ironed out tomorrow

PS I used to freak out at 220 and 230 too, but I wouldn't worry if it runs 190-210 and then goes up at lights, 220-230 is not really that hot or that big a deal. I wouldn't worry about shutting it down until it is in the 240+ range
Remember my little story about the broken motor mount? Better check yours, or at least make sure they are in proper. Reason being, it sounds like the engine may be shifted in the bay not lining up with the shroud. That is a long shot, but you never know.

It shoulds like you have covered every base possible. I would go with the fan and the relay kit from Pep Boys to get the cycle right where you want it.

You were asking about the amount of air behind the fan. The real trick is to open the hood, crank the car and put a shop rag on the headlight side of the radiator assembly. It should suck the rag against the condensor or radiator. It it just keeps falling off, you are not pulling enough air.

The fan blades should sit right in the shroud, with a finger width or so around the edges. The shroud needs to fit snug to the radiator support and radiator area.

It sounds like you get hot while cruising at speed.


Go to the bone yard and yank a lower air dam off a third generation firebird. Not the outer painted one, but the black plastic one that is about 3 1/2" tall and 30" wide. Figure out a real creative way to attach it to the bottom of your radiator/cross member assembly. It must be directly under the lower part of the radiator as much as possible.

Cruise down the highway and watch your temp drop off to almost nothing. This is a street rodder trick that almost always works. I also put one on my V8 Fiero project and cooled it off so much that I had to look for ways to raise the temp after that.
How did today go?? Any head way, running cooler?
Let us know your progress

The mechanic thinks that if we put everything stock again we should be able to cool it down.

I disagree! The fan has been offset and you cant go stock anymore.

But we have been trying to catch this gremlin for a while and just decided to let him figure it out before he gets frustrated from me making suggestions.

We had an edelbrock victor aluminum water pump that we found out was a reverse pump. A local guy did a switch aroo with the blades. I don't know if he connected it yet or not so i will let you know what happened on Monday afternoon.

I really hope he can make it work with the stock shrould cause i paid $280 for it! Bubba go ahold of the old one.

The only thing that has been really changed is the cam. Its got .47" of lift with 292 degrees of duration. Its go 2.02/1.60 valves that have been worked over. I noticed it does not have much low end response but when i take up to higher revs i can feel it. The guy estimates 370 hp but i want to put it on a dyno to get real numbers. Is his estimate correct?
reverse pump, switched the blades? Do you mean it was meant to turn the other way and so he changed the impeller. That would make a HUGE difference I believe.
As for the cam, I take it to mean 292 292 .470 .470. The lift at .050 and the lobe centerline could be make a difference, but for the norm this sounds like a cam with lots of overlap which should make for a pretty mean sounding idle, and should put the real power at higher rpms instead of lower rpms. You'll want a good low rear gear for something like that, especially with those big valves which will like the higher rpms too.
As far as the hp, I wouldn't even guess, too many things can affect it, CR, carb size, header size, etc... It could be a pretty strong motor though if everything works well together.
I hope the cooling deal is either fixed or fixed soon.
Good Luck,


We'll the mechanic gave me the car back, and guess what he figured out what was going on. It turns out that we were putting in a 17" fan. When i went to Autozone to buy a replacement fan it turned out that it needed a 18" or even 19" fan. Which shocked me cause we could barely make a 17" fit.

Well this is what he did to make the 18" fit. He put the heavy duty fan clutch and he put nuts between the clutch and the fan to back it up a bit, and it fits!! So I took it out with a " i have to see it to believe it attitude" and she barely went over the second notch on the gauge.

I went through 1 1/4 gas tanks cause i was so excited.

but there has risen a new problems. I put headers on the car and its heating up the starter. She won't crank after a long drive.

When i push her hard and i come to a stand still she also dies. What could cause this?

Now i have to battle the interior heat. Now that she has a true dual exhaust i am going to wrap the headers with exhaust wrap and also the pipes that run under the seats. I am also going to put a heat barrier cause d@mn she gets hot inside!

I have to take her back on tuesday so that he can put the rear bushings on the car and he is going to check and possibly change the rear gear to make her a better daily driver. I would like to go with a 3.5 or a 3 gear ratio. She is reading about 10mph above what she is actually doing. I think its in part to the tires, she has 245 60r15 and the rear gear. Since i live on the U.S./Mexico border sometimes i spend an hour and a half waiting to cross back into the U.S. for this reason as a safety precaution i am going to put an auxillary fan.

The mechanic wanted me to test out the car and see how i felt her.:) Boy am i LOVIN IT!!!!!

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