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Best rust treatment

I’ve been doing some research on the best rust preventative / treatment mainly for the undercarriage but also for small spots. Fluid film seems to be a popular choice that works reasonable well and is transparent for visible spots. But some people are saying crc works better but it isn’t transparent so it would only be good for the undercarriage but its thicker and lasts longer. Then there’re rust converters like this one also by crc
What do you think would be the best to deal with existing undercarriage rust and prevent more from forming? If these products live up to their advertising I’m thinking the rust converter followed by a rust preventing coating would be best. What do you think? Has anyone used these products or something else that worked better?

Fluid Film is a wax. Just as you was the paint on your car to protect it, this product would behave the same way underneath. The other two don’t really say how they protect the surface. My favorite rust treatments are a combination of a conversion coating and a paint. The conversion coating, like magnesium phosphate, are a mild acid that remove the remaining rust, then after the acid I see neutralized, coat the surface with the phosphate. The conversion coating is also a great preprint treatment, and after the paint dries, you get an excellent rust preventative. Don’t spray it twice, though. If you want a top coat on this, use a paint without the conversion coating.

Don’t waste your time or money.

Rust on the undercarriage is forever.

Rust showing up on the body panels is only about 30% of the rust that’s actually there.

Rust is like cancer. Once it starts, you’ll spend more money trying to prevent it than what the vehicle is worth.



Tester , beat me to it. If you are asking about rust it is too late.

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I go to a lot of old car shows a lot of the owners use POR15 on the undercarriage.

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Those don’t sound like daily drivers?


It will take a LOT of work and you won’t get all the rust covered but POR 15 works very well. Trouble is, you can’t even SEE all the rust, let alone get to it to coat it. Give it up.

They are not but they are cars that people want to last a long time. Some of them are driven a great deal in the summer. There are a lot of people that would rather have a 50s or older car that they can drive anywhere than a show winner and I think they enjoy the hobby more.

Won’t using a converter or coating or both at least slow it down? I know you can’t stop it but I would like to extend the life as much as possible. Especially with living in a salt state. If it really won’t do anything how long do you think it will last before becoming unsafe? Right now its 17 years old

Too bad Dagosa doesn’t check in right now. He was a frequent, very frequent contributor here and an advocate for rust prevention. Google some of his stuff on this site. Here’s a little sample…

dagosa Jan '13
“What do you mean about the rust dagosa?”
Most people think rust prevention is either a matter of just keeping the car clean by running through a car wash and/or having someone do a one time rust spray under the body, The second couldn’t be farther from the truth. Google “rust prevention by spraying” inner body panels with motor or linseed oil (for environmentalist) and inspecting drain holes and the insides of the vehicles. The real rust, other then body damage on the outside starts where the welds are from the body panels, inside. You do treatment once every two years. On a small compact it takes ten minutes…less time then a wash job

ALL body shop personel I have talked to in Maine (really only four shops) either do it to their own cars and/or others privately or recommend it to their friends. A conversation with some one in a body shop and Googling environmentally friendly options is worthwhile. You can no longer hire professionals to do it as it is not environmentally friendly if you use motor oil. Linseed and other organic oils work as well. Just a little education…I wish I had learned about this in my twenties instead of my thirties. MY CARS, SOME TEN PLUS YEARS OLD HAVE NEVER RUSTED anywhere. I get thousands more come trade in time…over a car with any rust through. The person that showed me this, has cars 30 plus years old with no rust that he still drives in Maine winters…Frame members can be painted with grease etc. as well. You will get dirty but I figure I pay myself $300 an hour in savings. Pretty good part time job, aaya aha.
_ A discussion here…_

BTW, if you do use motor oil and not organic, use fresh not used as others have mentioned and take steps to contain the run off to protect the environment…it is possible to do !

Dagosa wrote about this many times for years, swore by it.

I hate driving in salt during the winter. I found the perfect treatment for driving in salt and rusting out my car. I apply what is called Endless Summer. Just before the first snowflake every year I will now be joining all the other Snowbirds and heading to the Sun Coast.

In Canada,we use Krown rust treatment.Very effective stuff