Went through the first winter with the 24 Silverado. On my previous Chevys (04 and 13) I was religious about flushing the underbody every spring. They both still rusted in the usual Chevy spots. For this truck I plan on spraying between the bed panels (over wheel arches) and cab rockers with oil. Is it possible that doing all that flushing actually makes stuff worse? I mean with garden hose sprayer, I never trusted those car wash jobs. Is it possible that a vehicle would last longer if it was unmolested (with the exception of occasional oil spray)? I am referring only to the sheet metal. I’ll probably still try to hose the frame off? I’ve kept up with that pretty religiously with the spray stuff gm recommended to cover any imperfections in the wax coating (I can’t remember what its called, can is in the garage).
Underbody Flushing - Actually Worth It
- Thread starter CapitalTruck
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If you just spray the water yourself, the best time to do it is right after the salt accumulates. Rinsing the salt off with water is best done as soon after as possible.
The automatic car wash underbody wash should be good, since it can spray the entire thing underneath.
Even if it didn't 100% stop the rust, it still helped. Especially the 04, if that thing didn't completely rot, the spraying worked
You might also consider trying Krown's salt eliminator or a similar product.
The automatic car wash underbody wash should be good, since it can spray the entire thing underneath.
Even if it didn't 100% stop the rust, it still helped. Especially the 04, if that thing didn't completely rot, the spraying worked
You might also consider trying Krown's salt eliminator or a similar product.
I don't see how washing it with water can make it worse? That's what the oil spray companies do first, get the salty sand out of as many places as possible and then spray the oily stuff. In spots where the sand can build up, I've seen it wick away the oil and then hold moisture and then even spraying the sand with oil may not be enough to displace the moisture.
I think washing and then having the pro oil spraying done in the spring is a good idea, then spray a bit around yourself when you swap on the winter tires.
I think washing and then having the pro oil spraying done in the spring is a good idea, then spray a bit around yourself when you swap on the winter tires.
If you really want to keep the undercarriage rust free, when operated in a highly corrosive environment, I've found that continually washing the salt off the undercarriage throughout winter, is the way to go.
My results were the exact opposite. I bought a new Mazda B1600 truck in 1982 and washed it thoroughly most Sundays in the winter. Had to scrap the truck in 1996 because it was completely rusted out. Of course, the quality of the steel Mazda used had to do a lot with it.
With my present 19 year old Sierra, I don't wash it all in the winter. I have not washed it since December 2024. What I do is spray rust proofing oil on it every fall. It is holding up quite nicely. My goal when I bought the truck new was to keep it for twenty years. It has been so reliable and trouble free that I just might keep the truck for a few more years.
Your idea is the hypothesis that I go by. I think that excessive winter washing is of little value and is mostly a "feel good" thing. Why wash in between almost weekly precipitation. I also wonder if the undercarriage washing pushes salty water into places it otherwise might not reach?
I DO get my car Krown sprayed annually in late spring. I touch it up in late fall with an aerosol can, just hitting the high abrasion areas. Krown claims that a micro-this layer is retained even if it looks washed off. I only wash my car maybe 2 times over the 4 month winter period. Heck, I only wash my car about 5 times a year total. Less touching = less paint damage. Again, barely a week goes by here without precipitation (except for annual 3 - 5 week drought periods once in a while).
So, my single data point is that Krown oil spray and no winter washing maintains a rust free vehicle.
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Every single truck I have owned since my first I wash under the trucks extensively to get in the places mud and sand build up with more care and focus than the topside and enjoy seeing all the stuff that comes out knowing it would have just sat there for the life of the truck otherwise starting the process
These trucks have been thru typical Oklahoma or Colorado summer/winter depending when and where
The problem really lies in the Foam sound damping material they put directly above the wheel arch and the lower rockers the junk in most cases is open cell and holds moisture.....it's like they literally hope it rots away and you get to pay for the privilege
That being said I apply either boiled linseed oil or cheap 2 stroke and put it in a sprayer and get above the wheel arches from the inside and lightly spray a few squirts and let it slowly creep down and drip out the bedside at the very bottom ....... clean up the visible with de natured alcohol wait a few days and clean again then detail the truck
Keep the rust from starting in the first place is key
These trucks have been thru typical Oklahoma or Colorado summer/winter depending when and where
The problem really lies in the Foam sound damping material they put directly above the wheel arch and the lower rockers the junk in most cases is open cell and holds moisture.....it's like they literally hope it rots away and you get to pay for the privilege
That being said I apply either boiled linseed oil or cheap 2 stroke and put it in a sprayer and get above the wheel arches from the inside and lightly spray a few squirts and let it slowly creep down and drip out the bedside at the very bottom ....... clean up the visible with de natured alcohol wait a few days and clean again then detail the truck
Keep the rust from starting in the first place is key
Depends if it's coated yet or not. If it's still raw steel, then clean it up with degreaser, then rinse it. When it's bone dry, coat it liberally with CRC Marine corrosion inhibitor or PB Surface Shield or any of the lanolin based products.
Repair Geek on YT has gone over this in a handful of videos. Once it's coated, leave it alone or add more to areas that wear away. No more washing.
Repair Geek on YT has gone over this in a handful of videos. Once it's coated, leave it alone or add more to areas that wear away. No more washing.
Maybe washing it most Sundays in winter wasn't enough? That era of Mazda was highly susceptible to rust, however.
This is the vehicle I owned longer than any other. A '97 4Runner. I bought it new, and owned for 22+ years. It was operated on Salt encrusted roads every winter, and spent time on the Bonneville Salt Flats every summer. All I did was hose off the undercarriage and wash the body, as often as necessary. In the winter that could've been several times per week.
At any rate, it was rust free the day I sold it for a ridiculous amount of money, to someone who knew what it was, and was willing to approach me at a gas station, and make an offer to good to refuse.
The day I sold it doing an in-and-out through a dealer, to the new owner.
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The best rust prevention is to coat with something like Fluid Film, or Krown when new, before rust has started.
I put 2/3 of a 5 gal pail of FF on my van when I first bought it. I removed every body plug, washed and flushed everywhere. Drove it for a week in the summer and fluid filmed everywhere with the spray gun and 3' cavity wand. Then replaced all body plugs etc.
I touch up every fall, and keep from power washing the underside all winter.
It's 5 years old and shows absolutely no signs of rust yet. Roads are salted 5 months a year here in northern Maine. Even the DrawTite aftermarket hitch I put on still looks new, and those are notorious for rotting away in 4 years.
I feel that oils wash away, when I worked at a garage a few people put used oil/bar&chain oil/ATF, you name it on their vehicles. They rusted just as bad as everything else I had on the lift.
Petroleum based stuff wreaks havoc on rubber components under a vehicle over time. I have not seen that using fluid film. It all makes a huge mess though! But a mess is better than gone.
I hot water power wash my vehicles at least weekly all winter. Otherwise you can't even see out the windows here.
I put 2/3 of a 5 gal pail of FF on my van when I first bought it. I removed every body plug, washed and flushed everywhere. Drove it for a week in the summer and fluid filmed everywhere with the spray gun and 3' cavity wand. Then replaced all body plugs etc.
I touch up every fall, and keep from power washing the underside all winter.
It's 5 years old and shows absolutely no signs of rust yet. Roads are salted 5 months a year here in northern Maine. Even the DrawTite aftermarket hitch I put on still looks new, and those are notorious for rotting away in 4 years.
I feel that oils wash away, when I worked at a garage a few people put used oil/bar&chain oil/ATF, you name it on their vehicles. They rusted just as bad as everything else I had on the lift.
Petroleum based stuff wreaks havoc on rubber components under a vehicle over time. I have not seen that using fluid film. It all makes a huge mess though! But a mess is better than gone.
I hot water power wash my vehicles at least weekly all winter. Otherwise you can't even see out the windows here.
I guess that was the root if my question: “ I also wonder if the undercarriage washing pushes salty water into places it otherwise might not reach?”. That is a good articulation of it. I’m going to take the taillights and body plugs out of this thing and see what it looks like, then spray some oil in there and repeat annually.
My 13 year old Rav4 has minimal underbody rust. I try and get the car washed regularly during the salty Minnesota winters but sometimes it can be weeks before it's warm enough for the car washes to open. I have sprayed Fluid Film underneath a few times in the past but it's been a few years. So far I haven't seen any signs of rust on the pinch welds or the lower door panels.
Pull the oval plugs on the inside of the bed to gain access to the wheel arches and soak them with Fluid film or similar. Same with the rocker panels, pull the plugs out and let er rip.
I also do the frame everywhere its boxed, inside and out.
I also do the frame everywhere its boxed, inside and out.
Don't car washes tend to recycle the same dirty and salty water over and over ? I wouldn't want to spray that on my
undercarriage.
undercarriage.
If you live in the rust belt and daily drive in winter no amount of washing will save your car. As others have said you need to coat it with a quality rust preventative product. Then you actually stop washing underneath to preserve the product.
You need a wet film protectant like Surface Shield, Fluid Film or Woolwax-- all are lanolin-based.
Chevy frames (still! In 2025!) are just coated with some cheap wax that frankly sucks for rust prevention.
$100 a year or so for a wet film application, properly done, and you won't need to worry about running through car washes in winter time.
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