Rust-proofing exposed undercar parts

[XC92]

Yes, I know, there's no practical way to truly rust-proof anything on a car, but to the extent possible, how do folks rust-"protect" car parts that are exposed to the elements, especially on the underside? Most especially nuts and bolts, which get wrenched on during removal and refastening and thus any paint applied is likely to wear off fairly quickly. Sure, better ones come galvanized with zinc, but that too wears off after they've been removed and refastened several times. What do you coat them with or otherwise do to them to extend that factory rust protection?

I'm thinking either some phosphoric acid-based rust "remover" that chemically reacts with rust to form a tough gray-black rust-resistant layer, like Krud Kutter, or one of those zinc spray-on galvanizers, and either one after removing as must rust as I can. I know that some people swear by oily coatings like Fluid Film, but that just seems like a dirt and grime magnet that will create other problems. I'm looking for a "clean" solution that doesn't need to be cleaned up and reapplied every fall. This isn't just about looks, but preventing the fasteners from either seizing or disintegrating.

 

[Dusty Landrum]

Well I am currently right in the middle of doing this to my car. I use a lot of the techniques you have mentioned, but I vary which one depending on WHAT I am wanting to treat. So for me I took the metal down to bare metal for all frame related areas that way I knew I had a clean, rust free platform to start with. After I was at a bare metal state I applied two light coats of both a rust-reformer, followed by a self-etching primer. Once that was dry, I scuffed it up and the applied por15 over that. After THAT dried (which takes freaking forever btw, 96hrs I think), I scuffed up the por15 and applied a professional grade bed liner down over that. The process took like a week or slightly more total just on the treatment part, not to mention the process of actually taking everything down to bare metal. Oh and forgot that I also had to apply new seam sealer to ALL seams again and even some that didn't have it from the factory since the oem seams can be almost non-existent. That's just for the frame .

For parts/hardware I powder coat everything freaking thing I possibly can. Have the shop either media blast it or chemically strip it to bare metal and powder coat. To me this seems better than just having a zinc coated part because like you said, a small nick or whatever and the coating is compromised and exposes the metal. So literally, everything metal piece I would remove or whatever I have powder coated. Adds up of course in price but worth it to me in the long run AND looks of course. For hardware, this one was tricky for me. I bought every single nut and bolt I could oem so I know the quality and coating are "100%". Again, pricy and takes forever to run the part numbers but worked it out. On install I 100% added anti-seize to every single freaking thing. Anything that I put in had it. Obviously things that needed a little loc-tite didn't get it and really nothing can really do about that. I did use higher strength but removable though. For STUDS like the drive shaft and subframe for example, I used a scotchbrite pad to not mess up the threads but still knock of the oem paint and then repainted them with rust-reformer and then primer and THEN used anti-seize on the threads when running the nuts on and THEN sprayed the exposed stud left after the nut was run on with the galvanized zinc you mentioned up top. For some bolt heads and nuts that I knew were very low removal rates like the tank straps I sprayed a light layer or rust reformer over the heads to help to.

Oh, and for every single ground contact I removed it, used a dremel wire wheel and exposed bare metal, installed the ground with new oem hardware and then coated about a half-inch around the ground with stuff called aviation CRC. I have seen aircraft fly around for 20+ years and this stuff is still there and in tact with no corrosion, so figured it was good enough for my Eclipse too .

I know this is VERY long winded but hope this helps some people and yourself.

 

[DogWhistle]

Well I am currently right in the middle of doing this to my car. I use a lot of the techniques you have mentioned, but I vary which one depending on WHAT I am wanting to treat. So for me I took the metal down to bare metal for all frame related areas that way I knew I had a clean, rust free platform to start with. After I was at a bare metal state I applied two light coats of both a rust-reformer, followed by a self-etching primer. Once that was dry, I scuffed it up and the applied por15 over that. After THAT dried (which takes freaking forever btw, 96hrs I think), I scuffed up the por15 and applied a professional grade bed liner down over that. The process took like a week or slightly more total just on the treatment part, not to mention the process of actually taking everything down to bare metal. Oh and forgot that I also had to apply new seam sealer to ALL seams again and even some that didn't have it from the factory since the oem seams can be almost non-existent. That's just for the frame .

For parts/hardware I powder coat everything freaking thing I possibly can. Have the shop either media blast it or chemically strip it to bare metal and powder coat. To me this seems better than just having a zinc coated part because like you said, a small nick or whatever and the coating is compromised and exposes the metal. So literally, everything metal piece I would remove or whatever I have powder coated. Adds up of course in price but worth it to me in the long run AND looks of course. For hardware, this one was tricky for me. I bought every single nut and bolt I could oem so I know the quality and coating are "100%". Again, pricy and takes forever to run the part numbers but worked it out. On install I 100% added anti-seize to every single freaking thing. Anything that I put in had it. Obviously things that needed a little loc-tite didn't get it and really nothing can really do about that. I did use higher strength but removable though. For STUDS like the drive shaft and subframe for example, I used a scotchbrite pad to not mess up the threads but still knock of the oem paint and then repainted them with rust-reformer and then primer and THEN used anti-seize on the threads when running the nuts on and THEN sprayed the exposed stud left after the nut was run on with the galvanized zinc you mentioned up top. For some bolt heads and nuts that I knew were very low removal rates like the tank straps I sprayed a light layer or rust reformer over the heads to help to.

Oh, and for every single ground contact I removed it, used a dremel wire wheel and exposed bare metal, installed the ground with new oem hardware and then coated about a half-inch around the ground with stuff called aviation CRC. I have seen aircraft fly around for 20+ years and this stuff is still there and in tact with no corrosion, so figured it was good enough for my Eclipse too .

I know this is VERY long winded but hope this helps some people and yourself.

Very impressive. Your answer and process went way beyond the similar solution we would recommend for the OP. If you have a thread on this process, we would love to see results pics.

 

[danl]

I can second por15, works great for things that do not get exposed to sunlight. If exposed to sunlight, it requires an enamel top layer. I did a roll cage with por15 with no enamel and it was fine.

For bolts:

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[Dusty Landrum]

Very impressive. Your answer and process went way beyond the similar solution we would recommend for the OP. If you have a thread on this process, we would love to see results pics.

I have not done a thread on it but I do have everything in my build profile with pics. Maybe I should create a write up for it….?

 

[DogWhistle]

I have not done a thread on it but I do have everything in my build profile with pics. Maybe I should create a write up for it….?

Yes please!

 

[XC92]

Hey thanks, very detailed and thorough! At this point I'm basically looking to protect just fasteners as best as I can from rust, especially exposed ones under the car, e.g. cross and center member, control arm and subframe nuts and bolts.

The actual structural and suspension parts I'd already removed, thoroughly cleaned and derusted down to the bare metal, primed with a combination of rust reformer and self-etching primer as you did, and painted, adding a thick layer of undercoating to the road-facing surfaces. That seems to have mostly held up well, only needing a little touch up after nearly a year.

But the nuts and bolts, ech, just ech. I was going to remove all the rust and crud with a wire wheel drill attachment, the only question being what to then put on them to keep them from rusting again. Unlike parts, they're subjected to rubbing and scratching upon tightening and removal, and so need to be protected both chemically and mechanically.

I think I'll end up spraying CRC zinc spray on them, then maybe top coat them with clear coat. Or maybe I'll just zinc spray them and see how they hold up. The top coat would probably rub and scratch off when I tightened them. But then maybe they'd protect the zinc coating. I guess I'll just have to experiment and see what works. Maybe I'll top coat half of them and see what happens.

 

[Dusty Landrum]

I used the por15 seams sealer. I wanted something that was seal extremely well and would last forever. Definitely better than the oem crap the smeared around on the car. The por15 was super easy to apply and when it dried it was freaking ROCK hard. Again, takes forever to try so just have to be patient before you cover/paint over it.

 

[Red Rider]

I agree on how to treat components - blast, prime, paint, powder coat even better. Luckily I found a good local blaster that also powder coats. SHWEET!

Fasteners - I've been using a lot of stainless. Not OEM, but way better corrosion resistance, and probably cheaper too. If you want bright, look for 316, but other alloys are a little stronger. Several good internet supply houses out there, Bolt Depot is probably my most used.

 

[EC17PSE]

I re did some panels due to rust and its a bugger to get everywhere but most is possible. To get inside the rockers remove the rear interior panels off and go down the holes. This way you can also use a spray lance with a coating of choice and line the inside and hopefully stop any excess moisture buildup inside. Also make sure its not a non setting coating! Those suck and just attract dirt snd dust and not nice to deal with later on so get a fully hard setting one!

I went woth a brand here and its rock solid! I can hammer it and its not coming off so prep well and it will last you along time!

Clean every single multi layerd steel bit going as you WILL have rust in between them layers! The rear 2C trailing arm mount it 3mm thick and 1mm plate for side reinfocement but it rused through that! So i made it all 1 plate and no overlaps to prevent this, on all the other sections i seam sealed them all up so no more water can get inside and sit and rot it! Some bits you cannot do but alot you can! I did everywhere from under csr to inner wheel wells! Takes time but worth the results.

In the front fender area on a 2g is a gap on both sides with bolt holes in? No idea why its there and it does not have a cover so water can get inside and move along the inner upper rail! So my advise is make a plate and seal it off as i done this. I found no reason for it to be open and never needed it in my life so its a waste of space just waiting to collect dirt and water!

Zinc bolts help along way but eventually they will oxidize but are better then self color non zinc coated bolts. Where you can and NON structual use stainless A4 (aka 316) but use a good anti seize to help keep this from corroding inside, normslly aluminum permatex anti seize is great as i have used that for years and my Military friend uses it on the planes also without fail! So good stuff.

Blast and etch prime or powder coat what you can take off to help as mentioned above.

I have just spent the last year cutting rust out and sorting all this out over last year so its a paint but once done will thank yourself for all the messy hard work