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67 Sunroof
Samba Member
Joined: February 22, 2014
Posts: 1836
Location: Salisbury, MD
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 Posted: Mon Sep 10, 2018 7:25 pm Post subject: Why black paint? |
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Everything I have learned says that black paint absorbs heat....heck even when I wear a black outfit I get hot as hell!
So why paint our engines black?
I don’t understand the theory behind it if we wanna keep our air-cooled engines running as cool as we can?
Can someone explain what I’m missing? Thank you! |
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FullFender
Samba Member
Joined: October 25, 2014
Posts: 647
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| Posted: Mon Sep 10, 2018 7:28 pm Post subject: Re: Why black paint? |
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Very good point, I am glad you brought this up. All my tin is black, oddly enough CHT's remain fine. Interested to see what others say
Last edited by FullFender on Mon Sep 10, 2018 7:37 pm; edited 1 time in total |
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Glenn 
Mr. 010
Joined: December 25, 2001
Posts: 76904
Location: Sneaking up behind you
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| Posted: Mon Sep 10, 2018 7:34 pm Post subject: Re: Why black paint? |
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Who paints their engine?
Not the factory?
_________________
Glenn
74 Beetle Specs | 74 Beetle Restoration | 2180cc Engine
"You may not get what you pay for, but you always pay for what you get"
Member #1009
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modok
Samba Member
Joined: October 30, 2009
Posts: 26785
Location: Colorado Springs
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| Posted: Mon Sep 10, 2018 7:40 pm Post subject: Re: Why black paint? |
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the tins are black on the inside so they don't reflect heat back at the cylinders and heads.
you can see why chrome cylinder tins are not so smart.
i don't think the outside color matters much. i like machine grey
Last edited by modok on Mon Sep 10, 2018 7:43 pm; edited 1 time in total |
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Max Welton
Samba Member
Joined: May 19, 2003
Posts: 10697
Location: Black Forest, CO
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| Posted: Mon Sep 10, 2018 7:43 pm Post subject: Re: Why black paint? |
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The tin guides the air. It does not function to either absorb or reject heat.
The air inside the shroud for example has not yet cooled the engine. That air is still (relatively) cool.
OK fine. How about the over-cylinder tin? Most of that is inside the engine room. If it were to radiate heat, where would that heat go? Right back into the air in the engine bay, that's where. Then it would go back into the fan.
Bottom line is that it doesn't matter what color the tin is.
Except that maybe black hides dirt better. My floor is pizza colored.
Max
_________________
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Last edited by Max Welton on Mon Sep 10, 2018 7:45 pm; edited 1 time in total |
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modok
Samba Member
Joined: October 30, 2009
Posts: 26785
Location: Colorado Springs
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| Posted: Mon Sep 10, 2018 7:44 pm Post subject: Re: Why black paint? |
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Cool idea
They should paint toyota truck engines red so it hides the blood. Every one I ever fixed i end up bleeding.
Last edited by modok on Mon Sep 10, 2018 7:46 pm; edited 1 time in total |
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Glenn
Mr. 010
Joined: December 25, 2001
Posts: 76904
Location: Sneaking up behind you
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| Posted: Mon Sep 10, 2018 7:46 pm Post subject: Re: Why black paint? |
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The factory painted the tins black because black goes with every exterior color.
_________________
Glenn
74 Beetle Specs | 74 Beetle Restoration | 2180cc Engine
"You may not get what you pay for, but you always pay for what you get"
Member #1009
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rugblaster
Samba Member
Joined: March 31, 2016
Posts: 1170
Location: San Angelo, Texas
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| Posted: Mon Sep 10, 2018 8:01 pm Post subject: Re: Why black paint? |
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Black radiates heat. Look at wood stoves, they are not black by accident. But what about a black car being so much hotter inside than a white car sitting out in the sun? Start a fire INSIDE the black car and it will radiate more heat than the white car. Thermodynamics is a tricky bitch. It has to do with electro-magnetic radiation.
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ach60
Samba Member
Joined: May 14, 2001
Posts: 4139
Location: Santa Maria
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| Posted: Mon Sep 10, 2018 8:08 pm Post subject: Re: Why black paint? |
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The factory painted the tins black because black has good thermal Emissivity.
Emissivity is a measure of a material's radiating efficiency.
You want the heat out of the engine, you don't want the heat hitting the tin & bouncing back into the aluminum.
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Good Luck
Al |
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Glenn
Mr. 010
Joined: December 25, 2001
Posts: 76904
Location: Sneaking up behind you
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| Posted: Mon Sep 10, 2018 8:09 pm Post subject: Re: Why black paint? |
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| rugblaster wrote: |
| Black radiates heat. Look at wood stoves, they are not black by accident. But what about a black car being so much hotter inside than a white car sitting out in the sun? Start a fire INSIDE the black car and it will radiate more heat than the white car. Thermodynamics is a tricky bitch. It has to do with electro-magnetic radiation. |
What about at night?
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Glenn
74 Beetle Specs | 74 Beetle Restoration | 2180cc Engine
"You may not get what you pay for, but you always pay for what you get"
Member #1009
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Max Welton
Samba Member
Joined: May 19, 2003
Posts: 10697
Location: Black Forest, CO
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rugblaster
Samba Member
Joined: March 31, 2016
Posts: 1170
Location: San Angelo, Texas
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| Posted: Mon Sep 10, 2018 8:15 pm Post subject: Re: Why black paint? |
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| Glenn wrote: |
| rugblaster wrote: |
| Black radiates heat. Look at wood stoves, they are not black by accident. But what about a black car being so much hotter inside than a white car sitting out in the sun? Start a fire INSIDE the black car and it will radiate more heat than the white car. Thermodynamics is a tricky bitch. It has to do with electro-magnetic radiation. |
What about at night? |
Sleep.
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'69 Karmy, '69 Camper, Meyers clone, '65 drag bug, 10.78 @ 128 (sold it) '51 Dodge farm truck,
'09 MB E350 '18 MB E400, '65 Plymouth Valiant convertible and a '19 Ford F250 King Ranch (nicer, but dirty, farm truck)
VWoA factory trained line tech 75 till 90 or so
ASE Master Certification
VWoA Assoc. of Quality Technicians inductee (One of 25 in the five state southwest region)
La Confrerie des Chevaliers du Tastevin (San Angelo Chapter)
TCU ......GO FROGS!!!!!! |
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YDBD
Samba Member
Joined: February 25, 2017
Posts: 891
Location: Bavaria, Germany
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| Posted: Mon Sep 10, 2018 8:58 pm Post subject: Re: Why black paint? |
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This:
| ach60 wrote: |
The factory painted the tins black because black has good thermal Emissivity.
Emissivity is a measure of a material's radiating efficiency.
You want the heat out of the engine, you don't want the heat hitting the tin & bouncing back into the aluminum. |
I think even in the dark black will radiate more heat than other colors of the spectrum. Black cars feel hotter due to the emissivity, and cool faster. I always thought when my black car goes into the shade it will cool faster than another color.
Sound like a cool science experiment....
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Towel Rail
Horizontally Opposed
Joined: April 15, 2005
Posts: 4622
Location: SE CR IA US NA PE
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| Posted: Mon Sep 10, 2018 9:25 pm Post subject: Re: Why black paint? |
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| 67 Sunroof wrote: |
Everything I have learned says that black paint absorbs heat....heck even when I wear a black outfit I get hot as hell!
So why paint our engines black?
I don’t understand the theory behind it if we wanna keep our air-cooled engines running as cool as we can?
Can someone explain what I’m missing? Thank you! |
You learned it backward apparently. Black is the best absorber of light, which is why black things get hotter in the sun. But it is also the most efficient at radiating heat.
Bob Hoover was big on painting parts like engine cases, cylinders, and pushrod tubes with a thin coat of flat black.
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1974 Thing -- under the knife
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049 > 070 > 053 > 009 |
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ach60
Samba Member
Joined: May 14, 2001
Posts: 4139
Location: Santa Maria
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| Posted: Mon Sep 10, 2018 9:33 pm Post subject: Re: Why black paint? |
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| Max Welton wrote: |
| ach60 wrote: |
| You want the heat out of the engine, you don't want the heat hitting the tin & bouncing back into the aluminum. |
OK. Where does that heat go again?
Max |
Engine on:
Out, guided by the Sled Tin
Engine Off:
Absorbed by tin, radiated off into the engine compartment, and out into atmosphere.
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Good Luck
Al |
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jason
Samba Member
Joined: August 07, 2002
Posts: 3444
Location: Garage
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| Posted: Mon Sep 10, 2018 9:42 pm Post subject: Re: Why black paint? |
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| They painted it so it wouldnt rust. Im sure the sheen matters though. |
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vwracerdave
Samba Member
Joined: November 11, 2004
Posts: 15303
Location: Deep in the 405
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| Posted: Mon Sep 10, 2018 9:46 pm Post subject: Re: Why black paint? |
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The engine tins DO NOT radiate any heat. They only direct air where it needs to go. The color of the cooling tins has no effect on engine temperatures, and chrome DOES NOT make it run hotter.
The factory chose black because it is a neutral color that matches and body color. Black is also the cheapest paint color to produce.
Ever wonder why Henery Ford only offered the Model T in black?
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rugblaster
Samba Member
Joined: March 31, 2016
Posts: 1170
Location: San Angelo, Texas
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| Posted: Mon Sep 10, 2018 10:14 pm Post subject: Re: Why black paint? |
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The next time I remove hot valve covers, I'll just tell my fingers they are full of sh*t.
_________________
'69 Karmy, '69 Camper, Meyers clone, '65 drag bug, 10.78 @ 128 (sold it) '51 Dodge farm truck,
'09 MB E350 '18 MB E400, '65 Plymouth Valiant convertible and a '19 Ford F250 King Ranch (nicer, but dirty, farm truck)
VWoA factory trained line tech 75 till 90 or so
ASE Master Certification
VWoA Assoc. of Quality Technicians inductee (One of 25 in the five state southwest region)
La Confrerie des Chevaliers du Tastevin (San Angelo Chapter)
TCU ......GO FROGS!!!!!! |
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Xevin
Samba Member
Joined: January 08, 2014
Posts: 7624
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| Posted: Tue Sep 11, 2018 12:40 am Post subject: Re: Why black paint? |
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Here we go again.  
https://www.thesamba.com/vw//forum/viewtopic.php?t...a6e3ceb56d
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modok
Samba Member
Joined: October 30, 2009
Posts: 26785
Location: Colorado Springs
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| Posted: Tue Sep 11, 2018 3:13 am Post subject: Re: Why black paint? |
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