Datsun Roadster Forum-311s.org

Last year i had a local shop put thermal coated headers that I got from Dean on my 68 20000. (which are great) I’ve probably driven the car only about 50 miles since because I’m getting it ready to paint. Now I’m seeing a white chalky substance around the manifold where it bolts to the block. It is also inside the manifold. I’ve tried to attach pictures Any idea what might be causing this???

That is normal for aluminum in humid air. Look closely at your chrome, you may find some pitting going on. I did. I got a dehumidifier.

It looks like you might have had a coolant spill on the manifold at some point (?) When it dries, it can leave the white powder. Maybe from a spill or hose leak or from the manifold replacement process...? Was the intake wet when you got the car from the shop?

As for humidity and condensation I will lightly "fog" the intake manifold and manifold studs/nuts with WD40 or" Engine Store" when I put the cars up for the winter. I also hit the carb linkages and shaft pivots just to keep them oiled

I don't recall if it was wet when I got it back. If it was I certainly didn't notice. I'll try to remember to fog next time I'm putting it away for the winter.

That looks like corrosion due to dis-similar metals in contact with each other. Boats use zinc as a sacrificial anode to prevent corrosion in salt air. I agree that some kind of light, oil based coating might help (on the intake, not the exhaust mani). If the header was the only thing changed and the corrosion was not happening prior, perhaps that is what is causing it. You may want to make sure that the exhaust and intake manifolds are not touching each other- i.e. slightly grind down the intake if there is contact. You will still get continuity via the bolts and the head, but not as much as direct contact.