My 350Z has developed a white powder on the intake-manifold which I cannot seem to remove. I assume it is some form of aluminum oxide but various cleaning agents have done nothing at all…I recently tried white-wine-vinegar with very limited improvement. Has anyone else experienced this problem and can anyone suggest a solution? Thanks in advance, Shannon.

Welcome aboard, Shannon!

If it's not near the coolant ports, it is indeed simply oxidization. The bad news is, it's a bit of a PITA to remove without pulling the manifold.

You were on the right track with the vinegar/water solution (don't use white wine vinegar but standard cheap vinegar), AND also use a brush (stronger than a toothbrush, but not aggressive like a steel wire brush). A black nylon bristle brush (or a brass bristle brush) should do it.

Realistically, unless you're detailing it for sale, it's not hurting anything, and sometimes you can do more harm than good since the solution will get on other components...

If it were mine, I'd pull the manifold (maybe when you replace injectors), glass-bead blast it, and clear-coat with clear gloss paint or clear powdercoat. But again, more invasive than necessary unless you're selling or showing.

Great question!

To AZhitman... Thank you very much for your informative, if somewhat depressing, reply. My 2004 coupe only has 46k miles on it so I don't think it will need new injectors soon but I do try to keep it in "near show condition." I actually volunteer at SCCA Concourse d'Elegance shows as a judge and I am on the San Francisco Region Concourse Board so I'm pretty obsessive!!! Maybe this summer I will consider having a shop do the complete fix you suggested. Thanks again.
Shannon
PS: I did use a brass wire brush.

I totally get it... I've been known to dismantle a perfectly functional engine to beadblast, polish, and powdercoat components. Glad you're here!

Thanks again for your friendly and informative response.

White powder on the manifold sometimes indicates used of simple green to clean the engine compartment. The U.S. Army prevents use of that stuff anywhere its helicopters because it is corrosive to aluminum and the white powder is often indicating corrosion. Instead, use the aviation version of Simple Green which is not corrosive and safe to use on aluminum..