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Slowing down rust on auto frame and crossmembers

I have a 38 year old car, with some rust in the lower doors and inside the crossmembers. The top of the crossmembers seem relatively okay, but there are flakes of rust inside the lower openings of the crossmembers, which I can feel through large openings on either side of the bottom of the front crossmember. Fortunately, the bottom is not rusted through, as a screwdriver will not push through. I can scoop out some rust scale, but not all.

A car restorer suggested putting Ospho [affil links] in a plastic spray bottle, and spraying a mist inside the crossmembers through the openings on the bottom. There would not really be a good way to paint over it. I'm a little concerned about putting something like Por-15 Rust Preventative Coating [on eBay or Amazon] up there, as I think there are some mechanicals attached. Is it a good idea to use Ospho for this, in hard to reach places? Or would it maybe make the situation worse. I live in a fairly humid area, and I'm a long way off from any kind of major restoration, but this is a temporary measure to slow down the rust. I'd appreciate any advice from someone who has done this before.

Thanks.

Hank McNeely
car hobbyist - Parkland, Florida
2004

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March 19, 2009

Hi, Hank. Yes, I think Ospho or equivalent would be ideal for this. It is a very very thin coating that should not affect mechanicals at all, but it will convert the rusted metal to a more stable form. Good luck.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey