Hi,

got my first push rod tube cleaned up and would like to paint it with

hi-temp paint? any problems doing so?

tks

randal

Paint holds heat. They were plated gold or clear zinc.

hmm ..... now I have four painted..............

fresh paint should wire wheel off easily enough. too bad..... they look great

purple..............

tks

randal

Has anyone really done a study to find out how much heat is held in by paint?

If you google it, the answers are back and forth on both sides. The only argument I found that made any sense was that radiators are painted black because black color radiates heat better.

I have not seen any conclusive information that paint will affect heat soak. In theory, any applied surface on the tubes will have some marginal insulation effect. But paint is not considered an insulator or our homes would only have paint and not insulation.

I think the jury is still out on this urban legend...

BTW,
Kirchoff's Law of Thermodynamics basically states black (black body) absorbs better AND radiates heat better due to it's infrared properties. If this is the case, we should all paint our engines flat black.

just kidding about the purple....... they are black hi temp rattle can paint.

so the black will radiate the heat away like a radiator..... good........

they were developing some surface crud so I wire wheeled that off and thought

some paint would protect them for another forty years....


tks again...

r

I'm sure this debate is not over... But it's hard to argue against Kurchoff's Law. The only person that may have real world testing info on a T4 is Jake Raby. I'm sure he will chime in at some point.

Some of you are worried that a little paint on the push rod tubes will cause the engine to overheat?

The paint debate goes much deeper than just pushrod tubes...

If I was to add 40 holes in your house about 1 inch in diameter, it would be like leaving a window wide open.

So every little tiny incremental improvement using new chemicals, new knowledge etc can allow us to add more horsepower and reduce heat.

Things like paint versus zinc plating could add a few degrees and keep you from the full potential of the motor.


So yes, we argue about it, but it's so we can all learn.

What happens if I paint my jackstands?

(oops, I hope I don't get banned already…)

You will then have some cool looking Jackstands........but only if they match your car!

I painted mine.....
But masked off the o-ring seats. I wonder if engine paint is hotter or colder?

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and then installed....

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It it looks good then do it. Are you going to race the car professionally or compete in an endurance contest?

Not a racer, just a daily driver. Fastest I have had my car in these 1st 5000 miles is 75.... maybe. Not positive, cause the speedo is squirrelly.

Painting stuff ended up being one of those, "while your in there" things. makes you take your time during assembly. did not want to scratch the paint. And having a light color on the tins has helped me fined leaks etc...

Any thing that would fit in my wife's oven got painted and baked.

another shot of the engine on the table...


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All the oil that goes to the rocker assemblies, which is a lot, drains back through the push rod tubes. They're out in the cooling airstream, so they cool quite a lot, like eight tiny oil coolers. It's true that radiators are painted, but that's a special heat conducting paint that lets the metal conduct (and shed) even more heat than bare metal. That high-tech engine paint does the opposite, retaining heat. Bottom line there was a good reason VW zinc plated those.

Looks pretty good painted so try it, what the heck. Who knows, you might get away with it, especially if you never thrash the engine so shedding heat doesn't ever become critical. I wouldn't myself, but I'd be curious to hear how it turns out for you.

http://www.vw-resource.com/cooling_qa.html

"
Miscellaneous Ideas to Improve Cooling


All of us want a cool running engine, one that can take 70 mph into a headwind at 95 degrees all day.

The stock cooling system will handle higher power okay, but do include the thermostat and cooling flaps. (See our discussion of Cooling Vanes and Thermostat. If the thermostat is expanded, the flaps should be open, (as long as the control rod is moving freely).

Another useful trick is to examine the heads carefully, and use a Dremel or small chisel to remove any casting flash between the fins. This improves airflow for better cooling.

Paint the cylinders (not the heads) with a very thin coat of matt black heat resistant paint (brush-on, not spray paint -- according to John Connolly (Aircooled.Net), using the brush-on type is much better than spray-on, maybe it sticks better. Also paint the push rod tubes with the same stuff (that will cool the oil just a little, since it's just come from the hotter heads and is dribbling past the cooler cylinder air).

Don't be tempted to install those shiny "cool" aluminium rocker covers. The black VW ones shed more oil heat according to Bob Hoover. Apparently VW offered an Arctic Kit many years ago which included chrome rocker covers to slow the radiation of heat in cold climates.

If it's really needed you can alter the oil cooler doghouse to fit the wider Type 4 oil cooler.

Dave wrote to "Speedy Jim" asking about these methods to increase cooling. Jim wrote back -

Sorry. My personal feeling is that all of those measures are "lily-gilding". Any improvement is likely to be small and probably insignificant.

Many people install a larger oil sump in an attempt to reduce oil temperature. The Gene Berg catalog says that oils sumps aren't really effective in reducing the oil temperature. You only end up with more hot oil. The deep sumps don't have enough surface area to make much cooling difference. They were originally designed to prevent oil surge in hard cornering (racing), not for oil temperature reasons.""


and the debate continues............

my guess is that the thin coats (2) of paint a rattle can applies is nominal and

wont make much if any diff... just protect the surface from corrosion, hopefully.

Oil 'dribbles' back? Sure, at idle. Fifteen or twenty years ago I saw a video made by a guy who'd lost a racing engine from oil starvation, so one thing he did to find out what was going on was glue a plexiglass 'window' into a hole he'd cut into a valve cover. At high rpm's there was oil that half filled the rocker chambers, showing where a lot of his oil was going, and staying, at speed. Those pushrod tubes do more than you'd imagine. If you're determined to paint them my suggestion would be a very thin coat or two of flat black radiator or BBQ paint, at the most. But then again this is internet wisdom, so do whatever you want.

The old wive's tale of "Black gets hotter" or "Black radiates better" was made even worse by Dr. Iam Malcom in Jurrasic park.
We all know that the black interiors of our cars definitely get hotter in the sun, so why?

Just because the color "looks" black to our eyes does not mean that it is black as far as the Infrared spectrum is concerned.

Black is "Black" in the visible spectrum because it does not reflect light that we can see. It means nothing to the BIG contributor - Infrared.
The term "black body radiator" actually has nothing to do with the color of the radiator.
The term "black body" really means that the radiator has no actual color other than that which is due to the temperature and nothing else.

The real answer is that we dont know if one paint radiates better than another unless we can measure it's emissivity which requires a high tech instrument.
If a material absorbs heat good, it has a low reflectivity.
Flat Black paint might radiate heat better (high emissivity), but if it absorbs better (low reflectivity) than it will get hotter becuase it is absorbing the heat from it's surroundings better.

So to make something good at getting rid of heat you want high emissivity and high reflectivity.
Those two are often conflicting because a good radiator is a rough surface which makes it a bad reflector.

But keep in mind that heat moves away from the pushrod tubes three ways: Radiation (light), convection (moving air), and conduction (it's touching somehting else).

For this application the biggest contributor to cooling is the convection part. SO if you really want to make a difference, put some aluminum cooling fins on the tubes and orient them so air flows downward through them.

/Lecture

And we all know what happened to Dr. Malcolm in Jurassic Park!!

I went ahead and painted mine , I ended up using high heat brake caliper paint (rattlecan), I've haven't had oil temp issuses in awhile but then again I run two oil coolers , Bill D.

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What's with the plug wires?

Must be dual plug system?
Any details on that build?

And what exhaust do those stub pipes belong to?

Sorry, slight thread hijack, but an order of magnitude more important than the heat transfer of pushrod tube paint vs plating is the head casting itself.
Just been into cleaning up my newly acquired 2L 3 bolt intake heads (039-101-371A) and I noticed that casting flash had substantially blocked off many of the thru cooling passages between the fins. Lots of cleaning up with long drill needed to get flow passages opened up to intended areas. Photo shows area of concern. I did more clean-up after this, but you get the idea.
Click to view attachment

Note that my older 2L buss heads 022-101-372G were much better for flash.
So while you're in there folks look closely in those passages.

xx

Yes , it's my first attempt at a twin plug motor ( third gen of my 2.8 )

Details & pic's are forthcoming ( I need to make time to update my thread )

http://www.914world.com/bbs2/index.php?sho...225696&st=0

stubbs belong to my 7 year old 1 7/8 tangerine , they've been ceramic coated
inside for this build ,

sorry I don't want to hijack this thread , thanks Bill D.

Funny that I stumbled across this after this discussion.
It's about intercoolers, but applies almost exactly to the question here:

http://www.youtube.com/watch?feature=playe...p;v=f1QL9veQaNg

thanks for the link

Sorry, can't believe that, no way. Bare metal (aluminum anyway) convects heat best, and that's science. What manufacturer can you think of who paints their aluminum radiators or intercoolers? Radiator paint was used back when radiators were brass to reduce corrosion, which did reduce convection, but even unpainted brass transfers heat better than painted.

The only reason radiator paint came up in this discussion is that it's better than color paint, but for air cooled engine longevity the more heat transfer you can get the better, and that means bare metal. Zinc plated if needed to reduce corrosion, or if that's not viable then a conducting paint, usually a flat black. In last place for heat transfer would be color paint, but with that being said, damn that painted engine looks good!

I think that the point was: "Black painted aluminum DOES radiate heat better and that is a measurable difference." However the heat transfer due to convection contributes SO MUCH more than radiation, the overall difference between black and bare metal is insignificant.

You're talking about the point in that video, right?

Yes, and it also applies to this discussion.

1 - Yes black paint will help the push rod tubes radiate heat better (but they will also absorb heat better)
2 - The black paint does not change the convection properties at all (positive or negative) contrary to your comment:

"Bare metal (aluminum anyway) convects heat best, and that's science"

Although the truth is that certain surface preparations DO help convect the heat better if it increases surface area and does NOT provide an insulating layer. An aluminum flame spray coating would help convect heat better than a polished aluminum surface.
A rough plastic coating would HURT the convection because it would decrease conduction of the heat to the surface where the convection takes it away.

3 - The emissive properties of the tubes (painted or not) is meaningless because the contribution towards cooling is orders of magnitude greater for Convection than it is for Radiation.

So trying to optimize convection is a much greater return on investment than optimizing radiation.

In the video you posted the black paint really improved the heat transfer from radiation, but in this or that application who really cares about radiation?


Yeah, funny thing, I went back to look at the Mighty Mods video you posted and bless my soul if among the "you might also like" videos shown there's this one, "Mythbusting the Mighty Mods Black Intercooler Video" with an engineer going through the math and apparently contradicting both the conclusions in that Mighty Mods video and some of your points:

http://www.youtube.com/watch?v=z_mmmXTbLP0&sns=em

Those are twelve minutes of your life you'll never get back, but it seems better than going back and forth about it. In any case this horse is truly dead now, so to the original poster my advice is to ignore the science, ignore the conflicting advice and do whatever the hell you want.

That's exactly what I have been saying as well.


Nothing the engineer said in his video contradicts what I said above.
My explanation above was merely in response to your statement :


Martin Marietta (Now Lockheed Martin) patented the best "Radiator Paint" known to man.
It is called "Martin Black" and has been used to paint radiators by the military for years.
It is known for it's emissive properties but help cooling by convection as well.

One way to think of it is:
If you polish the metal surface really well, the air will move over it in a laminar flow and have little actual "contact time" with the surface.
If you make the surface rough by either sandblasting it, sanding/etching it or coating it you can make it transfer heat better by convetion than bare polished metal.
It does this by causing more turbulence near the surface.

So you CAN make a surface better at convection by changing it's surface properties.

Sandblasting or aluminum plasma spray would make a much more effective convective surface than polished aluminum.

Would a paint be better than polished aluminum?
Not likely if you choose your paint at random, but definitely possible.

OK, reality check. Stu, we're talking about push rod tubes. Push rod tubes. Not military, not the space program, not even aluminum. Push rod tubes. The OP's question is paint em (rattle can) or not?

OK, reality check. Keyser - First I said it doesnt matter.
Then you argued that it doesnt matter and stated I was wrong in my assertion that it doesnt matter.

You must have missid it where I said "the overall difference between black and bare metal is insignificant."

Then chose to argue.

Oh and to answer your question:



How about all of Setrab's oil coolers and a lot of Mocal's?
But they dont know anything.....

I just watched both u-tube videos and it seems like no one talks about natural convection versus forced convection. I could see how the black paint leads to a higher surface temperature resulting in greater natural convection and significantly lower air output temperature. Of course with a fan or a car driving forward natural convection would be insignificant. The guy in the engineering video says 3 degrees is significant, but my guess is 3 degrees is within their measurement accuracy of not only their thermocouples, but the hair dryer’s ability to provide constant flow and temperature.

So my understanding is that you want air flow with no separation for good heat transfer. The fins have to be spaced far enough from each other so the adjacent boundary layers don't interfere with each other while maximizing the number of fins. I assume the VW engineers spaced the fins based on “design for manufacturing” so the range of surface roughness, flash, etc. would not affect the flow patterns and boundary layer thickness around the fins.

So back to the push rod tubes. The tubes measure a bit less than an inch. I could use some input here, but from what I can find a Reynolds number greater than 10 results in the start of air flow separation for a cylinder shape. If 60 mph air (either from forward travel or the fan) is passing around the tubes, that’ll give us a Reynolds number of about 700. I assume if you have the warm air guides installed most of the airflow whether standing still or moving is from the fan. Does anyone the air flow velocity of the fan? In any case there appears to be very little convection heat transfer occurring especially since the downstream tubes are getting turbulent air. If there is any heat transfer in radiation I’d rather have hot tubes than the tubes radiating toward the cylinders. I’m assuming the tubes are hot because they have so little mass compared to cylinder, shielding, and other parts.

So maybe black is not so good, but bare metal or a light color is okay? Although I agree with everyone else that it probably makes no real difference.

I knew this would turn into a good debate...