mrmint69

I saw where if you headers are coated on the inside that you should replace the 02's after a while as the coating will foul them. My mid Pacesetters are coated on the outside but not the inside. Will this kill the o2's? Will it happen anyway as the heat will burn some residue off?

Z-RATED94

Might be a silly question on my part, but are you sure their not coated on the inside? My Pacesetter longtubes were, and I thought all coated headers were coated inside and out.

01Z

Maybe I shouldn't comment because I don't have them yet but I thought i understood that the coating was inside and out. The idea is to insulate and protect from moisture.

As for the O2 sensor question. Once again, I've read it more than once, the O2s can be ruined by the out-gassing of the ceramic when heated. The general consensus seems to be to drive it for a week or two and then put the good O2s back in. It would be nearly impossible to just remove and use a plug for that time and to find old O2 sensors for the break in period would be hard to do IMHO.

2000GTP

Its a hit or miss with the coating, if your 02s have alot of miles on them like mine did, then I wouldn't worry about it. If you get an SES light due to a contaminated 02 sensor, then just replace them.

Injuneer

The cera-metallic coating only works if its applied to both sides of the primaries. And it has nothing to do with moisture. The inner layer relfects the exhaust gas heat back into the gasses, so it can't travel through the tube metal to the outside surface. If the outside of the tube gets hot enough, it pours heat into the underhood area, and the high surface temp allows the iron in the mild steel to combine with the oxygen in the air and form rust.

An external "only" coating would not affect the O2 sensors at all.

The connection between the initial burnoff from the cera-metallic coating and the O2 sensors is sort of speculative - no one cold come up with a scientific explanation when we looked at this on the Advanced Tech forum. But it makes sense to play it safe and avoid installing brand new sensors for the initial startup on the headers.

01Z

Where I got the idea that the ceramic coating aka Armor*Coat acted as a moisture barrier was from the manufacturer's website.

Injuneer

They don't mention moisture at all. The "rust" is caused by elemental iron in the mild steel combining with the oxygen in the air at tube metal temperatures above 1,000-degF.

Its a popular misconception that header wraps cause rust because the wrap "traps moisture"..... that's not the case. With wraps, the tube metal temperature gets even hotter and rusts faster. Not from moisture, just from the excessive temperature.

mrmint69

How do they coat them? I looked at them and it is real shinny on the outside and the inside looks different then the outside. I would think they would dip or spray them.

01Z

Rust is 2 atoms of iron combined with 3 atoms of oxygen to form a new molecule - Fe2O3.

It is true that rust does not require water and that heat is the catalyst for the creation of this new molecule. However, not only is there a lot of oxygen in water, its presence provides for an electrochemical reaction.

Heat is needed for the electrochemical process in the joining of these atoms into the new element. Water greatly enhances that reaction by providing a good source of oxygen and acting as an electrolyte. Bonding an air/water tight barrier to steel will hinder the 2nd element from joining the iron. As far as I understand, the ceramic coating does a fair job of isolating the iron as well as insulating it from heat. Header wraps do as you said and make for even greater heat to initiate the process but they also hold moisture, the 2nd element and the electrolyte, against the steel after the metal cools. It's not a misconception as much as it is an incomplete understanding.

http://science.howstuffworks.com/question445.htm

Adding this for mrmint69. I appologize for diverting your thread. I'll stop at this point - I'm sorry.

LiENUS

I disagree on the header wrap, I believe water is only a factor on the inside of the pipe and in most cases it is not a factor on the outside of the pipe. Water is very much available for reactions inside the header pipe (its a byproduct of combustion), however on the outside the heat from the engine compartment tends to dry up water very fast, and header wraps tend to keep water out as much as they keep it in. But you are right in that water is not required for rust, an oxyacetylene torch essentially rusts the metal its cutting (you heat it up then hit the extra oxygen and it oxidizes the metal almost immediately and all the way through thereby providing the cutting effect). With an oxyacetylene torch you can be farely certain there is no water anywhere near what you are cutting as the heat dries out water very fast.

Z-RATED94

You should be sorry! You just hurt the few brain cells I have left.
And I too am sorry for leading this thread astray. It won't happen again............................................. .........................today.