Preventing rust in the Z's lower front fenders

[cgsheen1]

Our experience with POR-15 is that it adheres ridiculously well with metal surfaces when it's applied as they instruct. It was developed to adhere and encapsulate rusty surfaces in a marine environment. They have several products for conversion and encapsulation you might want to look at. We've used it on Z car floors, under cowls and fenders, in wheel wells, and in the area that you're trying to protect as well. But, keep in mind that we're in Arizona so, not a lot of wet here... POR-15 is UV light sensitive but in the areas I've talked about it doesn't require a protective top-coat.

 

[Captain Obvious]

Actually POR-15 claims to be flexible. Here's a snippet from their website:

POR-15® Rust Preventive Coating is an effective anti-corrosive and rust preventive coating that offers superior chemical resistance due to its dense, cross-linked molecular composition and non-porous attributes.

It has the opposite chemistry of ordinary paints. Now add to that POR-15® Rust Preventive Coating incredible hardness, toughness, and flexibility and you have a coating that is practically indestructible.

Clearly they can CLAIM pretty much whatever they wish, but "flexible" did make it into their marketing pitch.

[ETI4K]

I do love qualitative claims. 

One of my favorites is "water-resistant".  Everything is water-resistant - for a while.😁

[Captain Obvious]

Except water.  Haha!!

[CanTechZ]

This discussion got me wondering how much dirt and debris had collected in this area on my car. Since I'm working on a restoration, now was as good a time as any for the fenders to come off. While taking some before pictures it struck me that removing the mud guards in the front wheel wells makes it very easy to inspect and clean the area that @inline6is concerned about. In fact all that is really required is to remove the small rubber flap at the bottom of the mud guards.

 

I checked and it is possible to remove and reinstall the mud guards with the fenders on, there are only three M6 hex head screws holding them on. The upper screw is the most difficult to reinstall with the fender on, but using a m6 screw with a point made it not to bad. The rubber flap is easy as it is held on with two sheet metal screws. I used a magnet to hold it in place while reinstalling.

 

 

[inline6]

That is helpful information.  Cleaning that area out I think should be recommended regular maintenance as it is a real problem area on these cars.  I cleaned that are out on my first 240z (now a mostly track car) a few times over the years it was on the road after I restored it.  Even with new fenders, and the extra prep of using Glasurit zinc chromate epoxy primer and paint in that area (on the inside of the fender), 90% garaged time, driving only infrequently in rain, and the before mentioned clearing of debris a few times, the outside, bottom corner of the right fender has some tiny bubbles in the paint, indicating some pin holes are now present in the panel.  

I hope my modification on this car will eliminate this problem completely.  For what it is worth, regarding the comments about not recommending sealing that area 100% by some here, I note that there is about an 1/8" air gap between the inner reinforcement and the outer panel at the very bottom where the bolt hole is. 

The question for me now is, do I leave the 3 slotted vent holes I added?  Those are now entry points for water coming down the inside surface of the reinforcement panel.  I could close those up, and the air gap at the very bottom where the bolt is would still allow drainage.  

[ETI4K]

Try wetting that area (inside) and check it in a few days.  I'd think the diminishing gap between the fender and its support would still be wet.  And that is of course the problem.

I recall reading a study from 20 years ago(?) that garaged cars suffered faster corrosion rates than those left out in the dark and cold.  It seems the airflow around the cars tends to dry them out faster. 

To seal a pinch (spot) weld or a folded seam (even a Dutch hem) would require either immersion in a fluid with a low enough viscosity to permit capillary action so the liquid is drawn into the air space(s) and completely seal off the area from water/vapor - or a fluid such as cavity wax if it completely covers all ingress points and can be controlled so as to remain in place after application.  That's easy in a rocker panel.

@inline6   When you painted your fenders, how did you apply it to this space we're discussing?  I am always in search of improved techniques.  As an aside, I set up a test 3 years ago where I welded 2 pics of steel to form an L.  The joints were very tight, but welded only on one side, so there was a very small interstitial space.  I made 4 of them, then treated each differently with topical rust treatments (all from rattle cans).  I did this at a friend's.  I hung them outside on his fence to weather.  After one year some showed a bit of rust.  Then I moved away and forgot to check on them. My friend sent me an email recently to tell me his dad threw them away because he was tired of seeing them hanging there.  JHC.  Two years of testing gone, oh well.  What's not lost is Project Farm (IIRC) on YouTube.  The guy tests several topicals, and it may be of interest to you.

[inline6]

On my first 240z, with new fenders back in 1993, I sprayed chromated primer into the area we've been talking about.  I did not immerse the corner of the fender in the primer.  

For my 240z undergoing restoration currently, I used the existing fenders.  They had some rust in this area.  I cut out the rust and welded in replacement metal.  I also unfolded the metal that wraps around the reinforcement panel because some rust had occurred within.  As a result, the area captured by the folded rear edge of the fender had "expanded".  This happens when metal rusts.  It expands at the same time.  So, I unfolded the bottom two or three inches where the outer panel wraps around the reinforcement panel.  I manually removed the rusted metal that was loose from within the pinch, and then re-pinched the reinforcement panel.  This time, I poured the epoxy primer into the inside of the reinforcement panel.  And separately, I applied seam sealer to the outside of the pinch to seal the other side of it.  

So, that corner of the fender has been "soaked" in chromated epoxy primer on the inside, and seam sealed on the other side.  And of course, now it has a fabricated panel that hopefully will keep debris from settling into this trouble spot.  

The chromated epoxy primer I have been using is pretty bad-arse.  That said, again, I do not recommend relying on it (plus top coat) alone to save this area of our cars from rusting.

[Seppi72]

I'm almost beginning to think that the best thing we can do is to snake some 1/2" OD polyethylene tubing down each drain hole in the cowl and give each side a 30-second blast of compressed air (run through some desiccant drier first) each time we suspect it might have accumulated a bit of moisture; like when the temperature has dropped overnight and its humid.  That will guarantee our cars get the loving attention they deserve. Sorry, honey, I have to go give my Z a blow job.😖

[CanTechZ]

For reference here are some pictures of what my RH fender looked like when I removed it, before and after cleaning. When I did my first restoration on this car in 1982 and I had new fenders (from my local Datsun dealer) put on. No special sealing or rust proofing was done beyond what I think was a light prime and top coat over the factory primer. After 39 years only a small amount of debris had accumulated and after cleaning I found no paint bubbling and virtually no rust.  I guess I'm one of the lucky ones. Full disclosure, since 1982 only about 25K miles have been added.  After the first few years of light daily driving (no winters) it's been infrequent pleasure use only in good weather, but I have been caught in a few downpours.

Edited November 15, 2021 by CanTechZ

[inline6]

That is amazingly clean.  Love to see some others post up pics of this area of their cars "as found".   I may get some of my passenger fender on my first (now track) car, which unfortunately has been off the road for 7 years now.  I doubt I cleaned it out right when I put it in storage. 

[dutchzcarguy]

14 minutes ago, CanTechZ said:

Full disclosure, since 1982 only about 25K mikes have been added. 

If Mikes are miles..  😉  thats just a 1000 km a year.. i drove those as well in my 240z every WINTER!  and last winter the left fender came loose.. (lower rear end)  it was rotten round the bolt i guess.. the car needs a resto after it had one in 1998..  

I think thats normal wear on the fenders.. after the 280zx is ready maybe i make some new parts for the 240z fenders. sandblast the corner and repair whats necessary.

(Yeah i drive a 240z in the snow, better than a 300zxtt, that would be a pity..  also a 240z chassis is much easyer to protect and repair if necessary. Also a 300 would be all but problems due to his weight and a 240z is lightfooted and a blast to drive in the snow!)