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Rustproofing 2017 Chrysler Pacifica

Dear Car Talk,

Between May and September, I live little cottage about 200 yards from the ocean. I would like to protect the under carriage and engine of my 2017 Chrysler Pacifica from the salt air. Would I do any harm by spraying the entire under carriage and engine with WD-40, or any other rust protector?


Likely make a mess as it attracts dirt. Possible rot the rubber parts and make nasty smells from the exhaust. Don’t do it, it won’t help.


Cars in the rust belt, where they salt the roads, rust from underneath. More precisely, they rust from the bottom up.

Cars near the beach, where the air is salty, rust form the top down, so if I were you, I wouldn’t worry about the under carriage, and I’d focus on keeping the car washed and waxed. I’d wax it once a month between May and September.

I also think that a person might be fined for using sprays like oil and such near the ocean because of environment pollution .

Rustproofing is not an oil. It’s more like a wax. If properly applied - IT WORKS. And works very well. The problem is getting it properly applied…that’s the trick.

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And that’s why I have an Opel Astra from -95 without any rust. Without the rustproofing, it would have succumbed to rust many years ago.

Yes, that’s the tricky part, but at least you get the warranty.

Do not apply “rustproofing” to the underside of your vehicle, it does more harm than good. Most rustproofing materials are oil based, a very viscous sometimes tar like substance or a heavy wax like substance. These cause two problems, they trap any dirt or moisture to the surface they are applied to. Second they plug up the drain holes that water drains from the inside of your vehicle.

Removing the dirt, i.e. washing the vehicle is the first line of defense as dirt hold moisture. Remove the dirt and the surface can dry out. Applying a coat of wax to a clean surface will help by creating a barrier between the dirt and the paint. This helps mainly by providing a wear layer so that when dirt is washed off, it scratches the wax and not the paint.

There are some really good waxes now that will last up to 6 months or more but the best ones are a little more difficult to apply. I really like the crosslinked polymer (aka synthetic) waxes for durability.

Don’t worry about the engine, it is mostly aluminum and aluminum develops its own protective layer. It may not be pretty but it is effective.

Edit: When you wash your vehicle, run your sprayer along the bottom of your rocker panels, pointed up. The rocker panels rust out from the inside and not the outside where rustproofing is applied. Mud from driving during rain storms plugs up the weep holes for the rocker panels and water gets trapped inside. Using a hose end sprayer or opting for the panel wash at the carwash will wash the mud out and the rockers will dry out.

As I said…not properly applied. Properly applied rust proofing the technician first will block the holes before any material is sprayed. Then when done remove those plugs and ensure the drains are still working.

Again - not properly applied. Good companies will clean and DRY the undercarriage. I’ve seen it.

Don’t say rustproofing doesn’t work just because it wasn’t applied correctly. A good application of the rustproofing material WORKS. I’ve seen it. If I lived back in the rust-belt, every vehicle I own would get rust-proofed from a quality company. There are good ones around.

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Almost all new vehicles now come with a plastic bedliner type of coating on the rocker panels applied at the factory right after it has gone through the chemical conversion treatment so they don’t need further rustproofing. Plastic rocker panels are also being used to day.

And that is acceptable for 99% of the areas in this country. But the Rust-Belt is a special place. Cars rust out there…just not as fast as they use to, but they still rust out. Drive up there and look. You’ll see 5-8 yo vehicles that weren’t treated that have visible signs of rust. Those same cars here in NH will show no signs of rust.

I think you are going to find that they all have the same amount of rust, all other factors being equal. They rust from the inside out so applying more rustproofing to the outside will not do any good.

The additional rustproofing material will hide the rust longer but I also suspect that the drivers who would invest in additional rustproofing also take better care of their vehicles, washing them more often and washing the underside of the rocker panels and it is the extra care that is reducing the actual amount of rust.

I have looked…I’m there 2-3 times a year vising family. It’s not even close.

That’s why they (over here) also gets treated in any and all cavities.

As mentioned, cars typically rust from the INSIDE out. You are best treating the internal parts of the underbody like the rocker panels with something like this.

Just make sure things are as clean as can be and that you don’t clog up any drain holes.

Having lived in the rust belt all my life and traveled extensively across the country I would say Keith is right, in most of the country. In the real rust belt, Mike in NH is absolutely right. People who don’t live where snow totals can be 100-300 inches a year cannot use their 30 to 50 inch experience to understand our problems. I have rustproofing all over my car especially on all of the underside especially the brake and fuel lines. My mechanic showed me a pile of plastic gas tanks behind his shop where the metal threads of the fixture containing the fuel lines has rusted so badly it has eaten holes in the plastic threads of the tank.

Zinc Phosphate turns normal (red) rust into super (black) rust. It adds an extra oxygen atom to the rust going from FeO3 to FeO4. This is the same coating you will find on a well seasoned cast iron skillet.

It does work, but it is doing the same thing that the factory did when the panels were dipped or sprayed with Phosphoric Acid, also know as “chemical conversion bath” In the factory, a separate sealer is applied after the conversion process because the conversion makes microscopic cracks as it dries. In this product, the zinc serves this purpose as a sacrificial coating, like galvanizing. Not sure how their polymer works, but the sealer used at the factory is a polymer and it is applied while the panel is still wet, immediately after coming from the bath.


I have experienced 300" of snow in the UP.

It ain’t the snow who converts your car to a rust bucket. It’s the water when it melts (yes, 300 inches creates more water than 50, I know that) together with the salt that is a deadly weapon to cars. Here we average probably less than 15 inches of snow a year, but the rain and the salt does our cars in. Here, everytime the forecast warns of possible freezing temperatures, the salt shaker is out and about.
So far this has been a very mild winter so the last time I heard, they had only used 30k metric tons of salt.
Btw. here the cars pretty much always rust out from inside out.

From salty air near the beach? I think not. Cars at the beach rust from the top down.

What does a question about parking a car at the beach have to do with the rust belt?

Mike might be correct about the rust belt, but that relates in no way to the way cars rust at the beach.

No, but before I commented the conversation had left the beach.