Home made fan shroud.

-
Hummm.

I would think the paint would act like a barrier and slow the heat transfer?

I know bare aluminum transfers heat like crazy because when I cut it it's hot as hell all the way at the other end of the 4x10 sheet...
 
If 134 isn’t as effective than r-12, why don’t they paint a/c condensers black to give it that extra help?

“Guess that's why Chrysler painted all their rad. black huh ? Along w/ gm. ford, and all the foreign cars !l”
Probably because oxidized copper & brass would have looked shitty & caused complaining customers.
 
Last edited:
Cope said:
Hummm.

I would think the paint would act like a barrier and slow the heat transfer?

I know bare aluminum transfers heat like crazy because when I cut it it's hot as hell all the way at the other end of the 4x10 sheet...
Click to expand...

1. No. In heat transfer by radiation, black surface color is best.
2. You are talking about heat transfer by conduction and aluminum is excellent and copper is an even better conductor.
The third type of heat transfer is convection _ transferring heat from a material to moving air or gas. Here the most effective is a fin.
 
The science behind this dose interest me but in reality it's a moot point.
The shroud dosen't even get hot. So it's not radiating heat no matter what paint I put on it.
 
I do have copper sheets, now that you mention it, that would look bad *** and transfer heat....

:)
 
trapster said:
"Painting a radiator black would almost certainly make its performance worse. You have no guarantee it will be any blacker in the far infra-red, and the paint itself would act as a heat insulator degrading the radiators ability to transfer heat to the air."

You saw this part right ?
Click to expand...

You have a point that the paint may not be the most effective at cooling by convection, but the paint is so thin it won,t be much of an insulator.
 
Cope said:
View attachment 1715169213

Made this today to try and bring down my temp. It seems to help.
Click to expand...
You see that second bypass? The one that used to go to the heater.
What's it doing?
It's sending hot water back into the pump for a second go-round............
I plugged mine.

And what about that hose-splicer?
Did you do that to the bottom one too?

IMO, you're going from bad to worse.Put a monitor on that circuit; see if it ever shuts off.
It costs a lot of gas-money to run that thing full-time, what with the electrical conversion factor. How many amps does that thing pull? Would it be 20? 20Amps at 13.2 volts is 264 watts, or about a third of an electrical horsepower. But the alternator is only what? 20% efficient, so it's gonna suck at least 5 times that out of the crank, so 1.75 horsepower..... full time? Ouch.
But maybe it only draws 10 amps and maybe the alternator is only 10%efficient. Well then it comes to the same thing.Except now the alternator is converting 90% of it's output into heat..... underhood heat...... cooking your fuel line. What's gonna happen when the underhood air temp becomes the same, or higher, than the temp of the air coming through the fan?

That's like running small lawn mower under there at 50% power. You better carry a spare alternator in your roadside repair kit.
 
Last edited:
Those are some good points AJ.

I'll plug the heater bypass and see what that does.

I have a very large hole in the hood and no inner fenders, so under hood air temp should be less of a factor.

My temp is fairly stable now at 190 around town but it gets hot on the HWY. I think it's dead heading air on the right hand side. I'm gonna pull it apart (no small job) today, punch some holes and make rubber flaps on that side.
 
AJ/FormS said:
You see that second bypass? The one that used to go to the heater.
What's it doing?
It's sending hot water back into the pump for a second go-round............
I plugged mine.

And what about that hose-splicer?
Did you do that to the bottom one too?

IMO, you're going from bad to worse.Put a monitor on that circuit; see if it ever shuts off.
It costs a lot of gas-money to run that thing full-time, what with the electrical conversion factor. How many amps does that thing pull? Would it be 20? 20Amps at 13.2 volts is 264 watts, or about a third of an electrical horsepower. But the alternator is only what? 20% efficient, so it's gonna suck at least 5 times that out of the crank, so 1.75 horsepower..... full time? Ouch.
But maybe it only draws 10 amps and maybe the alternator is only 10%efficient. Well then it comes to the same thing.Except now the alternator is converting 90% of it's output into heat..... underhood heat...... cooking your fuel line. What's gonna happen when the underhood air temp becomes the same, or higher, than the temp of the air coming through the fan?

That's like running small lawn mower under there at 50% power. You better carry a spare alternator in your roadside repair kit.
Click to expand...

I know u get "out there" on some of ur surmising , but u have outdone urself this time !! LOL
 
Cope said:
Those are some good points AJ.

I'll plug the heater bypass and see what that does.

I have a very large hole in the hood and no inner fenders, so under hood air temp should be less of a factor.

My temp is fairly stable now at 190 around town but it gets hot on the HWY. I think it's dead heading air on the right hand side. I'm gonna pull it apart (no small job) today, punch some holes and make rubber flaps on that side.
Click to expand...
u just answered ur own problem. UNDER HOOD AIR IS FIGHTING THE AIR COMING THRU THE RAD. ! Disregard caps ----------
 
Hummm... never thought about that.
I just figured it all blew out the wheel opening or out the back of the car?

I have been thinking of making a plate and sealing the carb to the hole in the hood but I really thought all the fresh air from the scoop was helping..
 
AJ/FormS said:
You see that second bypass? The one that used to go to the heater.
What's it doing?
It's sending hot water back into the pump for a second go-round............
I plugged mine.

And what about that hose-splicer?
Did you do that to the bottom one too?

IMO, you're going from bad to worse.Put a monitor on that circuit; see if it ever shuts off.
It costs a lot of gas-money to run that thing full-time, what with the electrical conversion factor. How many amps does that thing pull? Would it be 20? 20Amps at 13.2 volts is 264 watts, or about a third of an electrical horsepower. But the alternator is only what? 20% efficient, so it's gonna suck at least 5 times that out of the crank, so 1.75 horsepower..... full time? Ouch.
But maybe it only draws 10 amps and maybe the alternator is only 10%efficient. Well then it comes to the same thing.Except now the alternator is converting 90% of it's output into heat..... underhood heat...... cooking your fuel line. What's gonna happen when the underhood air temp becomes the same, or higher, than the temp of the air coming through the fan?

That's like running small lawn mower under there at 50% power. You better carry a spare alternator in your roadside repair kit.
Click to expand...
AJ- great observations. Cooking the gas is a good one.
 
A lot depends on when your the scoop is on the hood and the size and shape of the scoop. It may be in a high pressure zone, pushing more air into the engine compartment at speed. It may be in a low pressure zone, actually pulling air out from under the hood.
An air dam under your bumper will block air from going under the car, thereby creating a low pressure zone underneath, sucking more hot air from the engine compartment.
 
Last edited:
It's a big Harwood scoop.


20180317_200227_zpsfllt9bnz.jpg
 
Dosen't the heater bypass just pump back below the thermostat?

I can't remember if it's an open passage or goes to the head?
 
Took the shroud off, punched some holes and added some rubber flappers.

20180515_165721_zpssvcsbzj9.jpg


20180515_165710_zpsntd5y4hu.jpg


I had to work on a customer engine so no road test yet. I'll road test in the AM. And report back.
 
RichB said:
Just fo the heck of it, I looked up emissivity factors. For radiant heat transfer, the emissivity of black paint is .97 to .99, while the emissivity of dull aluminum is
.20 to.30 . Big Difference! The emissivity of polished aluminum is only.05 .
I found this info on page 26 of Thermal Environmental Engineering by James K. Threshold. Color is important.
Click to expand...

People have argued about this for a while, and a few days ago I came across a similar question+answer asking why computer heat sinks were painted black. The answer basically said that at the temperatures they were operating at, the radiative cooling gained by the black paint was negligible. So I tried figuring it out for myself...

The short story is, I don't think the color really matters as far as cooling goes.

According to this page
Heat Transfer: Radiation
The emissivity of black paint is 0.9 and the formula for measuring the energy per unit area radiated away (Q) at temperature T is:
Q = 0.9 * 5.67e-8 * T^4​
Just to plug in some numbers, say the entire radiator is 212 degrees F (that's 373 K)
Q = 0.9 * 5.67e-8 * 373^4 = 987 watts per square meter​
My '64 Dodge's radiator core is 22x19 inches, or 0.27 square meters, so it radiates
987 * 0.27 = 266 watts of power​

Figuring out how much heat energy is given off from the coolant+air going through it takes more guesses, but I think it's reasonable. This page:
Stewart Components
says 189.5 HP of heat, which is 139,377 watts. Or about 500 times as much as is radiated.

Using their examples of 190 degrees F radiator inlet temp and 180 outlet, 100 gallons per minute (6.66 qt/sec) coolant flow rate, and my Dodge taking 20 quarts of coolant, I can guess how they came up with that 189 HP number. At 6.66 qt/sec, it takes 3 seconds to pump all the coolant through the system. The radiator has to cool it all down 10 degrees (5 degrees K) in 3 seconds to keep the inlet temp at 190. 20 quarts of water is about 19 liters, and it releases 4184 joules of energy to cool 1 liter of water one degree K. So to cool all that water:
19 liters * 5 degrees K * 4184 = 397480 joules of energy
power (W) = energy/time = 397480 J/ 3 seconds = 132493 watts = 180 horsepower​
Which is close to their estimate.

I'd say the black paint is to keep the brass from tarnishing and turning green, rather than to improve it's cooling ability.
 
Last edited:
You need to use the total surface area of your radiator for the radiation calculation, which is much more than the frontal area. It will include the tanks, the tubes, and the fin surface areas. Color may not make much difference in total engine cooling but black surface color is best for the radiant cooling.
 
you could just check it with a leaf blower, or a shop vac, you'll want those flaps to be pretty loose. :)
looks great by the way. Now I need one.
 
RichB said:
You need to use the total surface area of your radiator for the radiation calculation, which is much more than the frontal area. It will include the tanks, the tubes, and the fin surface areas. Color may not make much difference in total engine cooling but black surface color is best for the radiant cooling.
Click to expand...

You're right, I did only count the front of the radiator and not the whole thing. That might get you a little more than double: the back surface plus the tanks and sides. And yes, black is the best for radiant cooling. But I wouldn't expect the surface area of the fins to make any difference, since a material is just as efficient in emitting as it is absorbing, and when one fin emits some radiant energy, the next fin over that it's facing is going to just reabsorb it.

I was just trying to see for myself how much of an effect the radiant cooling has. Since the airflow is hundreds of times more efficient at removing heat, I don't think it makes any practical difference.
 
brummett said:
You're right, I did only count the front of the radiator and not the whole thing. That might get you a little more than double: the back surface plus the tanks and sides. And yes, black is the best for radiant cooling. But I wouldn't expect the surface area of the fins to make any difference, since a material is just as efficient in emitting as it is absorbing, and when one fin emits some radiant energy, the next fin over that it's facing is going to just reabsorb it.

I was just trying to see for myself how much of an effect the radiant cooling has. Since the airflow is hundreds of times more efficient at removing heat, I don't think it makes any practical difference.
Click to expand...

You also need to take into account the loss of airflow do to the paint.
 
trapster said:
You also need to take into account the loss of airflow do to the paint.
Click to expand...
I`m surprised no one has mentioned the super stock racers usedto run black engine blocks, claimed it dissipated the block heat better. Don`t know if they still do,but I know of one really successful that does> or did.
 
Dead horse.

Paint if you want. I enjoy the look of raw aluminum and I think its better for cooling.

I think the difference is so minimal that it dont make any difference. If painting an expensive aluminum radiator made it cool better the company's would be painting them.
 
You must log in or register to reply here.
-

Back
Top