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Clatter
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Joined: September 24, 2003
Posts: 7544
Location: Santa Cruz
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 Posted: Tue Apr 17, 2018 9:18 am Post subject: Best finish For Inside Heater Boxes? |
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Sitting here looking at these heater boxes...
Time to weld them all back together,
With some of that Thermal Zero insulation in there,
At least along the bottom of the boxes.
Still totally on the fence about how to go about protecting the insides of the boxes from rust,
Without fuming myself out of the car when the heat is on... 
Was thinking of having everything ceramic coated,
Then grinding to bare metal where the spot-welds go,
Then touching it up/doing it over after assembly..
But, two things with that
(other than the obvious cost/time factor).
1. Won't that stuff burn off and stink?
2. Ceramic insulates heat transfer!
Maybe the solution is to coat the inside of the shells only,
Then assemble everything,
Then have it all coated outside afterwards..
Had a set of fully assembled heater boxes ceramic coated once,
And they tumbled them in this ceramic media that was these little white BB balls..
They were forever wedged inside there between all of the fins,
And no amount if digging/blowing would ever get them out...
Maybe it's best to just assemble them in bare metal,
And have them done ouside afterwards.
The heat will always cook the water out of there anytime the car is run.
Factory heaters don't have any paint or anything inside to protect, right?
Anybody ever do this??
Yes, I'm crazy, but here i am at the finish line with these..
(No pun intended  ).
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ps2375
Samba Member
Joined: April 24, 2014
Posts: 2471
Location: Meridian,ID
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| Posted: Tue Apr 17, 2018 9:32 am Post subject: Re: Best finish For Inside Heater Boxes? |
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| Cerakote paint. I painted my header/muffler with it 2 yrs ago and it still looks the same as day one. It's air cure and no fumes. |
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scotty timmerman
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Joined: January 10, 2010
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Location: gigharbor W.A
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bugguy1967
Samba Member
Joined: January 16, 2008
Posts: 4341
Location: Los Angeles, CA 90016
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| Posted: Tue Apr 17, 2018 10:40 am Post subject: Re: Best finish For Inside Heater Boxes? |
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| Is there a reason they can't be black zinc plated? |
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raygreenwood
Samba Member
Joined: November 24, 2008
Posts: 21518
Location: Oklahoma City
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| Posted: Tue Apr 17, 2018 11:02 am Post subject: Re: Best finish For Inside Heater Boxes? |
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| bugguy1967 wrote: |
| Is there a reason they can't be black zinc plated? |
Yes....black zinc plating has a maximum continuous temp rating of a little over 425 F.
Bare zinc plating alone...has severely weakened anti-corrosion abilities over 212 F. It has to be oven baked at 500 F to dehydrate it. That helps but it makes it brittle and susceptible to thermal cracking.
With the base zinc having a nice tight crystalline grain structure...the use of the zinc blackening agent adds a metallic water produced salt to the surface. It has teh same problem. As it dehydrates....the crystalline structure cracks and flakes off.
I already went there years ago when searching for a proper blackening agent for cylinders. Black zinc will fail quickly and corrode fast.
One of the best methods for keeping rust at bay inside of the exchangers...is to go ahead and assemble them....and then ceramic or high temp enamel coat the outside..whatever you prefer. This way you have a clean, high temp integral coating of the outside.
When that is done and cured....dip the entire part in a light acid. You can do this with diluted 50/50 muriatic acid.....or even cleaning vinegar (6% acidity)...but the vinegar takes about a 3 hour soak.
Do not neutralize the part after the acid drip. Rinse it well and let it dry. Heat it if you can to about 200F. This will promote flash rust on the bare metal inside.
Then use a phosphoric acid solution...diluted. First dip....give it about 2 hours and then rinse it off and let dry. Then repeat and wipe off the excess on the outside to not mar the paint...and let it dry 24 hours.
The phosphoric acid will convert that flash rust to iron phosphate which will seal teh surface. Its not rust proof forever....but unless the inside of the exhcangers see very wet conditions without heat rapidly burning off the water...they will remain rust free for a long time.
You will get a slight amount of residue burn off smell for about 50 miles. This will keep the inside from rusting for about 3-4 years. I am sure by that point you should have some maintenance to do....so pull teh exchangers off...clean them...and repeat the phosphoric acid dip.
They can last nearly forever this way. Ray |
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DeathBySnuSnu
Samba Member
Joined: August 25, 2012
Posts: 1183
Location: MS
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| Posted: Tue Apr 17, 2018 6:16 pm Post subject: Re: Best finish For Inside Heater Boxes? |
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Cerakote thermal transfer on the inside.
Cerakote thermal insulate on the outside. |
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raygreenwood
Samba Member
Joined: November 24, 2008
Posts: 21518
Location: Oklahoma City
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| Posted: Tue Apr 17, 2018 9:51 pm Post subject: Re: Best finish For Inside Heater Boxes? |
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| DeathBySnuSnu wrote: |
Cerakote thermal transfer on the inside.
Cerakote thermal insulate on the outside. |
Yeah...but you cannot apply it with any precision...inside.... once its tack welded together....and you cannot properly weld it if its applied in advance.
Either way....it leaves the crevices or tack weld spotw bare which are the most rust prone.
Just use a water thin rust converter on the inside. Its also a damn site cheaper than $80 a pint....though Cerakote is a killer product. Its the assembly of this part that makes it difficult to use on the inside. But its perfect for the outside. Ray |
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yamaducci
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Joined: March 30, 2010
Posts: 2335
Location: Mount Airy, Maryland
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| Posted: Wed Apr 18, 2018 11:41 am Post subject: Re: Best finish For Inside Heater Boxes? |
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One of the weld through primers or corrosion protection aerosols should work well.
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busdaddy
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Joined: February 12, 2004
Posts: 51144
Location: Surrey B.C. Canada, but thinking of Ukraine
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| Posted: Wed Apr 18, 2018 3:26 pm Post subject: Re: Best finish For Inside Heater Boxes? |
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I've always used plain old Tremclad or Rustoleum, it's never burnt off (except when directly on an exhaust pipe) and some is going on 20 years just fine.
Why not put the shells together with nuts and bolts or pop rivets to allow easy dismantling for inspection every few years?
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Clatter
Samba Member
Joined: September 24, 2003
Posts: 7544
Location: Santa Cruz
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| Posted: Wed Apr 18, 2018 4:30 pm Post subject: Re: Best finish For Inside Heater Boxes? |
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Some great suggestions so far..
Thanks for your time, guys.
I'm really leery of using something inside the boxes that will be burning and stinking.
Anyone who has lived with an old set of these in the winter will know what I mean.
(What eye mean  )?
If I had a chance to test a few boxes, I'd be more willing to try something that was a paint or other coating.
Only ceramic coating have I actually run inside a heater box,
And the stink eventually went away.
Ray,
Why do you recommend using an acid prior to the phosphoric treatment?
I had heard that a light coating of rust was good for starting the iron phosphate conversion,
So why not just get them wet, or leave them out overnight in the dew, or something?
I'm leery of using acid on some boxes that just got painted on the outside...
Surely the phosphoric acid stink would go away fairly soon.
Using it on other stuff, it can really burn the eyes if not diluted.
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raygreenwood
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Location: Oklahoma City
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| Posted: Wed Apr 18, 2018 10:38 pm Post subject: Re: Best finish For Inside Heater Boxes? |
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| Clatter wrote: |
Some great suggestions so far..
Thanks for your time, guys.
I'm really leery of using something inside the boxes that will be burning and stinking.
Anyone who has lived with an old set of these in the winter will know what I mean.
(What eye mean )?
If I had a chance to test a few boxes, I'd be more willing to try something that was a paint or other coating.
Only ceramic coating have I actually run inside a heater box,
And the stink eventually went away.
Ray,
Why do you recommend using an acid prior to the phosphoric treatment?
I had heard that a light coating of rust was good for starting the iron phosphate conversion,
So why not just get them wet, or leave them out overnight in the dew, or something?
I'm leery of using acid on some boxes that just got painted on the outside...
Surely the phosphoric acid stink would go away fairly soon.
Using it on other stuff, it can really burn the eyes if not diluted. |
Because of two reasons
1. Acids.....will dissolve ALL rust down to bare metal....quick. its the fastest way to get rid of all crusty rust.
2. Phosphoric acid rust conversion treatments are 100% worthless.....unless they have something to convert. They offer 0 protection by themselves. They MUST have SOME iron oxide to convert to iron phospate.....or they do nothing. Just a waste of money.
And.....the use of an acid like muriatic....or even a long soak in strong vinegar.....causes hydrogen embrittlement of the metal surface. While this causes destruction and cracking of "rare earth" metals......it simply makes ferrous metals......susceptible to flash rusting due to breaking down surface ionic bonds and leaving a lot of free hydrogen and oxygen hond sites ready to bind with water and rust.
But flash rusting.....is only a couple of microns thick. Let it flash rust.....and then treat it with phosphoric acid.....and that very thin, even layer of rust is converted to iron phosphate....which is pretty damn rust resistant, especially in areas that are not just soaked with water and have enough heat in them to drive away moisture.
Using an acid first.....makes a very evenly flash rusted surface instead of just a patchy mess.
Its not as rust resistant as it could be if you treated it and painted it......iron phosphate surgave conversion is just qbout the worlds BEST primer for a wide range of coatings.
This is exactly what the prime industrial purpose for black phospate coatings is.....rust resistant, high adhesion primer.
The phosphoric acid residue will burn off faster than almost any paint.
If you are worried about using a "light" acid on something just painted.....then the paint is worthless. 
Acids will not affect good, properly cured paint. Caustics.....like sodium hydroxide......will affect paint.....not acids.
By the way....do not use strong acids on parts that have surface spring tension....like springs and sway bars and torsion bars....or even CV shafts. That hydrogen embrittlement makes them susceptible to cracking. Ray |
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