Heatshield Paint Flaking

Comer · June 10, 2004, 15:34

Did anyone prime their manifold heatshield before painting them?

I've used 2 cans of Hammerite paint which is resistant to 625C but it flakes in the same place each time.

Anonymous · June 10, 2004, 15:39

did you not use that acid ectch primer stuff?

Comer · June 10, 2004, 15:42

No. Who makes it? The Hammerite can states that they recommend that no primer is used before using their paint. Probably so that mugs like me get though cans of the stuff s:roll: :roll: s:roll:

Anonymous · June 10, 2004, 16:03

You can get it from halfrauds... but dont take my word for it... its just what i heard someone saying... if it all goes to pot blame Coley or something! s:wink: :wink: s:wink: s:lol: :lol: s:lol:

Comer · June 10, 2004, 16:15

Cool I may give it a go if I can be @rsed to rub it all down again! Thanks for the advice. If it fails I'm sure it won't look as cr@p as it does at the minute.

markiii · June 10, 2004, 16:17

wsire brush will strip it off in no time.

Anonymous · June 10, 2004, 20:45

You can get Acid-Etch Primer from Halford, it isnt a Brand as i remember.

Jap GT300 · June 10, 2004, 22:19

10 coats of Halfords extreme manifold spray is what i've used!

Anonymous · June 15, 2004, 23:14

when painting the heatshield, surely its not a good idea to paint it black as this will absorb heat and keep the engine bay hotter? i would have thought a bright colour (chrome/silver) would be better as they reflect heat

crankshaft · June 16, 2004, 12:49

Hi,

Is this Halfords acid-etch primer ultra-high temperature too ??

If not then wont it will flake off and take whatever is ontop of it ??!

Crankshaft

Jap GT300 · June 16, 2004, 15:33

Quote from: "Tomr2"when painting the heatshield, surely its not a good idea to paint it black as this will absorb heat and keep the engine bay hotter? i would have thought a bright colour (chrome/silver) would be better as they reflect heat

We're painting the outside black. The heat is generated from the inside so it won't make sufficent difference I wouldn't have thought.

Bongo · June 16, 2004, 16:26

Black surfaces absorb and give out heat quicker than silver ones don't they?

Tem · June 16, 2004, 17:53

Quote from: "Bongo"Black surfaces absorb and give out heat quicker than silver ones don't they?

Yes, but since you're not converting the metal itself to black, you're adding a coat of black paint on top of it. So you have to also consider how the heat transfers from the metal to the paint first.

Bongo · June 16, 2004, 19:16

Then black paint will absorb heat quicker and give it out quicker than, say, silver paint?

Anonymous · June 16, 2004, 23:27

absorbing heat quicker and transfering it quicker doesnt really make sense to me? s:? :? s:?

Anonymous · June 18, 2004, 18:25

It's basic priciples of heat transfer - the heat is being radiated from the manifold and being absorbed by the heat sheild - if it's black it will absorb and emit the radiation more readily. Think about black leather seats in the sun and white or light coloured leather in the sun - black ones burn your arse more s:wink: :wink: s:wink:

Anonymous · June 19, 2004, 00:10

understand that perfectly clear rusty, think you misunderstood me. i meant how can the black paint give off heat quicker than light coloured paint.

i know black will always be the more absorbent to heat

Bongo · June 19, 2004, 00:12

For the same reason that it can absorb more heat i guess.

I suppose you could compare it to a pipe - a bigger pipe will take in water quicker and spew it out quicker s:crazyeyes: :crazyeyes: s:crazyeyes:

Anonymous · June 19, 2004, 00:18

here's an idea s:idea: :idea: s:idea:

how about spraying the air intake tube and air box a light colour? would this not benefit when sitting in traffic and with the baking hot ait sitting in your air box? as i imagine it gets quite hot on those sunny days...

Bongo · June 19, 2004, 00:27

Covering it in some form of silver insulation ala DP might be even better s:? :? s:?

Tem · June 19, 2004, 12:31

Also, about the black/white thing in the sun, you're mixing two things. Yes, black gets hotter in the sun, because it absorbs all visible light frequencies, while white reflects all of them. But heat is NOT visible light and thus doesn't care about visible colors either. If you heat black and white pieces with IR, they both heat up the same.

The heat transfer is affected by colors too, but the color itself doesn't cause it, the stuff in the color makes the difference. A white surface generally lets about 95% heat through and black 96%, so no real difference. Best heat transfer coat is asetylene ash (I wonder if straight translation from finnish is right) with 97%, for comparison bare aluminum only lets some 85% through.

So painting a metal with any color transfers heat better than bare metal. So if you want to keep the heat in, don't paint it. Obviously there are special stuff to do the reverse, but this goes for normal paints.

Whether that 10% difference makes a real difference or not, I doubt it...