Fancy water "drain"

[Toploader]

So finally the rust has had "it's way" with the top of my two front fenders on the '86 MGM coupe...........no way I can pull the fenders off the car to address the issues.......and frankly for a street parked ride on NYC streets, it what will be. It amazed me that the rust started from the inside out.........so now when it rains the water just enters and exits LOL........the car would really be a total rust bucket had it not been for the original owner having the selling dealer send the car out to have it "rust proofed" I am surprised that no anti rust compound was sprayed at the tops of the front fenders........just the lower portion and rockers.

The only thing I did was steel brush the area, use some POR-15 on top of "Tiger Hair".......and then paint the area.

I envie all who have garages, and live in the SW part of the country.

Any person who buys a new car only to leave it on the streets of NYC is crazy:-(

[gadget73]

There is a seam in there where two layers come together right at the top of the wheel arch. The water gets between those pieces, and thats why it rots from the inside. Nearly impossible to prevent, and once it starts you're pretty much screwed.

[IPreferDIY]

I don't know about the older panthers, but my whale has two fender liner bolts near the top of the wheel arch (more like in the corners I guess). If you take the bolts out, you can get a straw from a rust inhibiting oil spray can in there. Bend the straw into an S shape to shoot in horizontal directions. When I did mine (though with the fender liners out while doing upper control arm bushings), I did lots of WD-40 first, the red runny Rust Check oil second, and the thick Rust Check oil third. This pretty much brought a stop to the rot.

[DerekTheGreat]

...It amazed me that the rust started from the inside out.........so now when it rains the water just enters and exits LOL........the car would really be a total rust bucket had it not been for the original owner having the selling dealer send the car out to have it "rust proofed" I am surprised that no anti rust compound was sprayed at the tops of the front fenders........just the lower portion and rockers.

That's the way it goes and why it rots. Moisture is the enemy and combined with an accelerator (salt) it's even deadlier. Since nearly all coatings applied from the factory are water based, over time the water softens them and reveals the precious steel. This in turn mates with the magical oxygen in the water and creates blisters and then holes. Anywhere the water can't immediately drain out will be where the rot spots happen. The insides of body panels aren't as well protected as the exterior because the Ecoat & pretreatment layers aren't as thick/uniform and they may not be as clean as the exterior since the cleaner baths and whatnot can't get in there so well either. Pretreatment+ecoat is the most responsible for corrosion protection after the substrate choice, then the primer, basecoat and clearcoat provide UV protection for the Ecoat and such. The exterior is what has to pass the warranty standards of whatever the manufacturer sets, so the interior of those panels only has to be good enough to resist perforation for that period. Underbody/hood areas have even lower standards. Why I say if you see rust on any of the exterior panels it's going to be 2x+ worse where you don't see it, and that's where it matters most.

[Toploader]

Thanks for this very informative explanation........why is it that new cars or newer cars, seem to not rust like the old?.........more plastic in rust prone areas??

That's the way it goes and why it rots. Moisture is the enemy and combined with an accelerator (salt) it's even deadlier. Since nearly all coatings applied from the factory are water based, over time the water softens them and reveals the precious steel. This in turn mates with the magical oxygen in the water and creates blisters and then holes. Anywhere the water can't immediately drain out will be where the rot spots happen. The insides of body panels aren't as well protected as the exterior because the Ecoat & pretreatment layers aren't as thick/uniform and they may not be as clean as the exterior since the cleaner baths and whatnot can't get in there so well either. Pretreatment+ecoat is the most responsible for corrosion protection after the substrate choice, then the primer, basecoat and clearcoat provide UV protection for the Ecoat and such. The exterior is what has to pass the warranty standards of whatever the manufacturer sets, so the interior of those panels only has to be good enough to resist perforation for that period. Underbody/hood areas have even lower standards. Why I say if you see rust on any of the exterior panels it's going to be 2x+ worse where you don't see it, and that's where it matters most.

[Toploader]

Never knew this.......thanks for the info

There is a seam in there where two layers come together right at the top of the wheel arch. The water gets between those pieces, and thats why it rots from the inside. Nearly impossible to prevent, and once it starts you're pretty much screwed.

[Tiggie]

New cars get e coated which is basically dipping in paint with an electrical charge on the body that attracts the oppositely charged paint. Gets the paint everywhere. Then they get better paint as well. More quality control when painted as well because it's done by machine and not a man. There were lots of bare metal areas on my 68 that paint just couldn't get to!

[gadget73]

Cars prior to the 80s were absolutely horrible in terms of rust problems, mostly because of all those bare spots. Even stuff in the 80s wasn't necessarily amazing, but was usually better than earlier cars.