Just got a pre-owned '15 f250 (6.7L) for our farm. We've had trucks before of course and all eventually get rust damage in varying degrees. I decided I'm going to take better preventative measures to hopefully keep this one looking sharp as long as possible. It will see alot of different conditions, mud, gravel, snow, highway etc.

Underbody areas I've decided I will spray down with some form of undercoating(or bed liner).

The rocker panels and fenders are my main concern. I'm considering Linex and Upol Raptor, but unsure how high to coat (those familiar with the body style understand how high up the body line is!) I plan on coating the inside of the fenders with something as well. Linex would obviously cost more than a DIY.

Secondly, would good mud flaps protect the truck equally well? Or just make it more prone to rusting at the mounting locations?

 

Do not undercoat the undercarriage, all it does is hold in moisture and salt and helps corrode metal faster. Go online and buy a fluid film kit and repeat once a year, I've been doing this for years now and my truck is like showroom new still

 

See if you live close to one of their locations.
https://www.krown.com/en/locations/

 

Second both of the replies from T diesel and SuperDutyScaler.

 

I use fluid film and my 4 1/2 year old truck has no rust anywhere. Plowing in the salt belt too. I use to use bar oil but fluid film is my current favorite.

 

Do these coatings attract dust? The gravel roads and field roads around here get SUPER dusty. But there does happen to be a Krown place about 35 minutes away!

The film or Krown seems like a decent option for under the body, but obviously wont prevent rock chips to the rocker panels. It might stop those spots from rusting, but wont stop the chips itself. I Looked at some mudflaps online... seems that a good set of 4 would cost me more than a Upol Rator kit...

 

I had Krown applied in early October, the underside and the inside of the truck and the inside of the bed looks brand new. I do not drive dirt roads very often though. I first heard of the product on South Main Auto youtube channel. In the video he states he drives dirt roads every day and does show the outcome.

I also purchased a can and have used it on spots on my travel trailer and on various spots on the weight distribution hitch. I sprayed the joints on the trailer steps and some surface rust, from driving in Ohio (snow and road salt), on the side of the steps that are directly behind the tires. The product seeped into the the metal making the entire step assembly look brand new even though I didn't spray the whole thing.

I am going to make an appointment to get my wife's car sprayed also.

Mudflaps probably are your best bet since you could periodically take them off to clean and treat the area.

 

Good mud flaps (big, ugly, wide ones) do protect your truck from flying rocks. Running boards (not tube steps) help, too. I second the use of Fluid Film and yearly reapplications as needed. There is no such thing as a one-time application rustproofing product. You must inspect the truck yearly and reapply....And avoid any tar-based, dries-hard-as-a-rock products.

 

Actually with fluid film you want to drive down a dusty road after applying it. I'll power wash my trucks undercarriage within the next week or two. Let it dry for a few days and then apply fluid film. The following day I'll drive down a farmers lane I hunt at to get a nice dusty coating over the newly applied fluid film

 

Another vote for Fluid Film....great stuff!

 

What area of the US is considered the salt belt? I live in Oklahoma and the DOT salts and sands the roads in snowy weather. When an Ice Event is in the forecast they spray the roads with a liquid solution prior to the freezing rain. I'm fairly sure that product contains salt by the looks of the undercarriage of my winter vehicle.

 

That liquid de-icer is the worst stuff ever for damaging your vehicle because it gets into every nook and cranny.

I'll add another vote for fluid Film. My truck has been through five Winters and it's almost spotless underneath, only areas with some surface rust are the axles(didn't spray them the first year and the front axle has bad prep so the paint flakes off), the leading edge of the track bars, and the parts that come pre rusted from the factory (steering gear and tow rod ends).
I reapply twice a year and usually do it all in one day. I think there really is no need to let everything set becausei think the fluid Film disperses water.

 

Lots in Maine use Fluid Film but I tried something different last year, Corrosion Free.
It's DIY and an option is a spray gun with a few different tips, and wands, 360 degree etc.
It lets you get inside doors and rocker panels.
It's non-toxic, displaces water, and seems to hold up so far.

https://corrosionfree.com/store/rust...l-1g-jug-only/

 

So with Krown or fluid film its ok to power wash, even under the truck?

Would a small strip of bedliner on the exterior of the fenders and rocker panels hurt? Even if I have the Krown or fluid film done as well?

 

I think you should be fine with just water but I wouldn't add any detergent to the treated areas.

Not sure what the actual outcome would be over years with the liner applied but both products creep into the metal and displace water. I would feel comfortable lining it if it were me.