License Plate and Rust

[V1]

While washing my car today, I removed the rear license plate to wash underneath. What I noticed were some very small high spots outlining the edges of the licence plate. They resemble pieces of sand underneath the paint, and I'm afraid it's the beginning stages of rust.

Does the metal-to-metal contact of the license plate and the car accelerate corrosion? Or is it more a factor of water and dirt getting trapped in there? Or both?

 

[Vuser]

It could be a bit of both. Our plates are steel, so I always paint the backs of them with Rust Oleum or similar paint. I saw my in-laws' tags, and the condition of them made me glad I do paint the plates of our cars.

 

[W8inDE]

I good way to keep the license plate off the paint and prevent scratches/rust is using small bushings. Get a couple at HD or Lowes, along with some stainless steel screws.

Also, wax behind your plate, and if you want to get real anal, wax your plate.

 

[Vuser]

I agree. I only wish that ALL vehicle makers would make the front bumper with an indentation for a front plate. Because of the flimsy plastic brackets they put on cars. And seeing those cars where the owner just drilled into the bumper to put the tag on the bumper directly looks ghetto.

But it would be good if they would have also made the spots for the plates have four holes instead of just the two.

 

[Vuser]

The stainless screws are definitely the way to go also. I don't know how large your screw holes are, but the size I buy are the 1/4 inch diameter. Lagscrews in winter since they hold to the clear covers I use then better, and Phillips screws for the frames only I use in summer.

 

[Mickey_M]

Stainless steel screws can precipitate rust. They will never rust, but since they contact the plate and the vehicle they can set off an electrolytic process in which the steel in the car sacrifices itself.

Generally you want to avoid having dissimilar metals touching each other. Here's the galvanic series:

http://www.corrosionsource.com/handbook/galv_series.htm

Metals to the right on the chart will tend to sacrifice themselves to protect metals to the left of them.

I spray the back of plates with cold galvanizing. I then use plastic stick-on bumpers from the hardware store on the backs to get a stand-off from the vehicle. I then use nylon screws to fasten the plates to the car.

The zinc galvanizing protects the plate, the stand-offs and nylon screws insulate the plate from the vehicle, and there is an airspace between the plate and the vehicle to cut down on moisture.

 

[Vuser]

I lost a plate once when I'd scored a parking lot bumper. It cracked the nylon screws I did have on it at the time. Not enough right away, but down the road a few miles due to the bumps and the screws broke off finally and woosh went the plate.

 

[W8inDE]

quote:

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Originally posted by Mickey_M:
Stainless steel screws can precipitate rust. They will never rust, but since they contact the plate and the vehicle they can set off an electrolytic process in which the steel in the car sacrifices itself.

Generally you want to avoid having dissimilar metals touching each other. Here's the galvanic series:

http://www.corrosionsource.com/handbook/galv_series.htm

Metals to the right on the chart will tend to sacrifice themselves to protect metals to the left of them.

I spray the back of plates with cold galvanizing. I then use plastic stick-on bumpers from the hardware store on the backs to get a stand-off from the vehicle. I then use nylon screws to fasten the plates to the car.

The zinc galvanizing protects the plate, the stand-offs and nylon screws insulate the plate from the vehicle, and there is an airspace between the plate and the vehicle to cut down on moisture.

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I have the same setup, using rubber bushings as my 'standoff.' The screws go through the bushing and give a nice clearance between the plate and paint. I'll have to try the nylon screws. Interesting chart about the metals. I learn something new everyday

PS, take off the plate and wax behind it (or use Klasse as I do). I also put sealant on my plate, which should prevent it from rusting.

 

[Vuser]

For lack of a better term, are the nylon screws "self tapping" or are they flat on the end like machine screws?

 

[kanling]

So what is the best kind of metal screw to use (instead of stainless steel) if plastic bushings or nylon is not an option? Just a steel screw with some kind of galvanized coating?

 

[Mickey_M]

quote:

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Originally posted by Vuser:
For lack of a better term, are the nylon screws "self tapping" or are they flat on the end like machine screws?

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They look more or less like regular machine bolts, but are nylon.

 

[Mickey_M]

quote:

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Originally posted by kanling:
So what is the best kind of metal screw to use (instead of stainless steel) if plastic bushings or nylon is not an option? Just a steel screw with some kind of galvanized coating?

---

If you can be non-conductive (any plastic) that's best.

Otherwise pick a metal that neither the license plate or car body will sacrifice themselves to protect. Galvanized would work.

 

[Vuser]

Are the screws the makers of the screw caps/covers put in with the kit of this type?

 

[Vuser]

I bought a set of screw caps yesterday, and surprisingly they fit over the stainless screws I already had on the tags.