Undercoating a car that has already seen winter use
 

I do not drive very much (about 5k/year on my 911, around 2.5k on everything else), including in the winter, but I do some. This car was in GA 1993-98, MI 98-08, my garage 08-16 and now in IL. There is no more than surface corrosion anywhere but it does have the look underneath you'd expect of a car driven in the midwest - surface rust under flaking paint on some suspension components, surface corrosion on hardware, etc. (except for the right front suspension, which has been protected by a slow power steering fluid leak). I would like to have the undercarriage coated to protect it from further corrosion. Product TBD - maybe Fluid Film, maybe something else. (I'll probably consult the recent thread on this topic.) Do I need to do anything to the car other than power wash the underside to make sure it is clean? Or am I better off not coating it at this age?

Once rust is there it will keep going unless you can 100% isolate it from oxygen.

I'd be afraid of coating over it, looks good on visual inspection, but the tin worms keep working...

Power washing or steam cleaning might be a good idea for a start. Cleaning the under carriage would let you get a more clear picture of the rust situation. Plus some places covered by dirt can harbor and promote rust underneath. Some rust is normal. Unless you see spots where rust is an obvious concern, I wouldn't be overly troubled.

I think some of the commercial rust proofing actually sticks better to rusted parts than non.

Used motor oil, been doing it for over 30 years. Remove all panels and spray away, messy but very effective. Use an old electric paint sprayer. Drive her down a dusty dirt road after that and it seals great. Owned cars for over 20 years that I still have and NO rust has appeared!! It works!!
I got Russian Steel in my cars! It stops rust at it's tracks and it costs $0.00.

@id10t, the car is practically immaculate by midwestern standards - all of the rockers, wheel lips, etc. are perfect. The bottom edge of the decklid is rusting at the weld seam because water gets inside via either the center mount for the decklid spoiler or the gasket on the light housings (I forget which), and there is some rusting on the door hinge pillar below the lower hinge, typically from leaf buildup that you forget about. Underside is perfect. The stuff I am describing on the underside is of the paint-flaking-off-control-arms variety and on hardware. There is nothing on the floorpan.

Oil penetrates those seems used oil works take my word for it!!

Cosmoline in a spray can. It penetrates and runs into cracks and spaces that the rubberized undercoating cannot. When dry it leaves a durable waxy coating. It also does not hide/cover further corrosion. I bought a case for about $40.

You can't do anything to the rust without removing it totally, the cosmoline will slow it down.

I have an 83 original owner with 65K ,miles. I have only driven mine in winter a few times -not by choice. I always thought the undercoating of my 83 was impressive. I opted out of any aftermarket undercoating because the dealer told me the body had a 7 yr guarantee against rust, which was better than most cars at that time, So here is a pic taken 10 years ago of my car - I was having the trans re-built.

I do wash the underside, wheel wells, etc of my car every year just because. http://forums.pelicanparts.com/uploa...1479247102.jpg

Then coat away!

This stuff turns rust black. Read up about it. Might give you some peace of mind.
https://www.amazon.com/Permatex-81773-Rust-Treatment-oz/dp/B000HBNX38

I get my truck sprayed every year with an oil type product. My 10 year old truck looks brand new underneath.
The only downside is I have to park on the street for a week while my truck drips.

Read up on fluidfilm. Its lanolin based rust preventative. Smells like sheep, used by navy. Non toxic and cleans up with soap, creeps into crevices. I bought their kit with spray gun and wands and treat my trucks once a year. A gallon does two SUV sized trucks including frame and door pillars. Don't bother with the aerosol cans, they don't go very far.

Seems to have stopped rust from spreading. Clean everything first to get dirt and debris off the metal.

@zakthor - thanks. I've saved myself a link to the recent thread that discussed this, but I do like Fluid Film. I have some in spray cans and find it useful for my bikes in the winter.

I would use Fertan for what you propose, it comes in trigger sprays and in cans.I use it on my cars which are used in horrible northern English weather. Removing suspension arms etc makes it much easier to coat them thoroughly: saying that, the front ones on my 944 were only about $18 each so I replaced them( and rebushed them at the same time

Here's my 06 Tahoe. I bought in North Carolina 6 years ago. I've oil sprayed since I bought it before winter. These pics I took today one week after being sprayed.http://forums.pelicanparts.com/uploa...1479436926.jpg
http://forums.pelicanparts.com/uploa...1479436961.jpg