Dealing with underbody rust

[A_DAB_will_do]

I'm just about to take possession of a used '98 Chevy C3500 (1ton) dually. It's got a diesel engine and about 120K miles. It already has a steel diamondplate flatbed installed on it. will post pictures in a few days.

During my pre-purchase inspection, I found the underbody of the bed is rusted, but not badly flaking or suffering from holes or any serious reduction in material thickness. In other words, rusty, but structurally sound.

I'm debating what to do to prevent any further rust and decay. There's a Ziebart shop down the street that does underbody coatings. I stopped by and talked with the manager briefly this morning. For ~$330 they provide a service to coat the underbody. First they wash, then spray on a rust coverter, then allow 24 hours to dry. They then spray on a thick underbody coating to anything that doesn't move or get hot.

What are your opinions of this stuff? Is it worth while at the quoted price? What are the pros or cons as you all see them?

Should I just let the truck go since it's already middle aged; and just replace things as they rust away?

What do you folks recommend for protecting the deck and headache rack on the flatbed? Right now the deck is bare metal with minimal rust. The headache rack has some unknown black paint on it, with some evidence of bubbling and at least the beginnings of rust.

What other methods have people used to prolong the life of their rigs? I saw another thread where a paint called POR-15 was recommended. How's this stuff take heat, sun, scuffing/scraping, and sparks?

Thanks for the replies.

[Tim]

I haven't used Por-15, but from what I've read, it requires a top coat of something else (paint, bedliner, undercoating) to protect it from the sun and possibly the elements. Unfortunately the worst places for rust tend to be where you have the poorest access to, and moisture along with water retaining debris tend to accumulate. The Ziebert work sounds reasonable, assuming its done thoroughly enough. Can they get access to the spots that really need it? Bed or body mounts for instance? Personally, I believe that unless you than seal something thoroughly, a yearly wax oil type spray is the best as it creeps into cracks and crevices just like the water and is self repairing, doesn't chip off or lift and allow water to accumulate beneath it.

[David R]

Just spray it with oil a couple of times a year or less. The rust will stop and it will last. LOOK at the brake lines front to back and see how bad they are. I buy 50' of brake line at a time and do a lot of em.

I coated a gas tank in a ford van that was pretty well shot 8 years ago. Its still going with the same tank in it. I used Wellworth "Mighty Lube". Its a synthetic grease that has a solvent carrier. The solvent evaporates and the lube stays for ever.

I don't believe in Zbart or the rest. I worked at a car dealer we installed Rusty Jones. It was worth less.

That thick coating they put on will harbor salt water and help it rust in spots.

Just my opinion and experience.

What motor?

David :)

[farmersamm]

Gotta agree with David R. Undercoatings suck. It's a scam.

Best thing to do is make sure all the spring hangers, and other spots that collect mud etc. are cleaned out so the water can drain and doesn't sit in the crud and make for a continually damp area.

[A_DAB_will_do]

Tim, David, Samm,

Thanks. I was leaning in that direction, but it never hurts to ask what others have seen. I'll see what I can find in the way of spray oils, like the Mighty Lube David mentioned.

Now that I've thought about it some more, the rust conversion coating is probably makes the rust into a phosphate coating. In a previous career I worked with phosphated and oiled bolts. The phosphate makes for a surface that's easier for the oil to cling to. Hmmm, I might look for something I can brush and spray on myself; and then coat the underbody with oil.

A friend of a friend works in a bodyshop, I'll give him a call and see what they recommend....If nothing else maybe I can get access to their lift to make getting under the truck a little easier...

Thanks everyone.

Oh, the engine is the 6.5L diesel, no turbo.

[Sandy]

In order for a rust converter, like phosphoric acid, to work on flaky rust it needs several things. 1st and foremost it needs to get in and under the very deepest of the rust, otherwise you're just converting the surface. With some guy waving a wand around and spraying I doubt that happens consistantly.

[Oldiron2]

Now that I've thought about it some more, the rust conversion coating is probably makes the rust into a phosphate coating. In a previous career I worked with phosphated and oiled bolts. The phosphate makes for a surface that's easier for the oil to cling to. Hmmm, I might look for something I can brush and spray on myself; and then coat the underbody with oil.Your idea about phosphate is good but Sandy's point about getting all the rust ''converted' is also true. If it's a problem, pressure washing or sandblasting can get excessive or loose rust off, but neither is always practical and to get a phosphate coating to form on clean steel is harder than converting a very thin oxide layer so the sandblasting can actually over do it.
A good coating of tar on clean, bare metal might last for years; underground pipe is/was treated that way--but you don't have clean bare metal and that Ziebart coating may not be equivalent to hot-dipped tar in that it may be porous.
I like the phosphate conversion followed by oil. You can get phosphoric acid for that purpose at paint stores, if it's not readily available elsewhere.

[Dualie]

Best I have ever seen as far as preventing rust is 1 part used motor oil to 2 parts diesel fuel. Use a cheep garden sprayer and thoroughly coat everything on the underside of the vehicle. makes a mess but keeps it from rusting and its low cost.

[A_DAB_will_do]

After a good night's sleep I'm thinking you all have it right. I know a professional sandblasting outfit, but I have doubts about doing this to the truck without taking the bed off. Too many moving parts and places where sandblasting could do more harm than good.

I also have some concerns about spraying anything on the truck that might be flammable. I'd be really annoyed if I barbequed the truck because grinding sparks or cutting slag set some coating on fire. There are some eco-friendly water-based oil emulsions that are used for rust preventatives. The coating goes on, and the water evaporates, leaving a thin layer of RP behind.

I wish the flatbed had been galvanized when it was new. This would have made it last forever...no use wishing for what you can't have...

[Oldiron2]

Remember the thread about electrolytic cleaning of metal parts? Know any abandoned, foreclosed homes with a swimming pool that is accessible to the truck bed??

[bigmookied]

POR-15 only requires a top coat if it is exposed to direct sunlight, so on an underbody it is not required. The nice thing is is goes a long way and is hard as anything to remove when cured.

For the money I would go that route, might cost you $60 with the acid to wash it first.

[specter]

We use POR products all the time on GE' ECO Motion locomotives. Great Stuff. As already said if the surface will be exposed too direct sunlight you will have to use the Topcoat or get the POR formulated for directed sunlight.

[metalmeltr]

most likely the zibart stuff is what bodymen know as rubberized undercoating, bodymen also swear at this stuff because it gets hard then it falls off so I would not use it. to protect from further rusting I would use eastwood's rust converter then a coat of paint, eastwood's rust encapsulator or eastwood's chassis black. www.eastwood.com

[specter]

Almost anything is better than Zeibart. If Zeibart gets cut or nick water gets under it and the coating holds it there creating more rust. Eventually then the Zeibart falls off leaving a big hole. Shops like Zeibart cause it fast and relatively easy to put on and charge the customer alot. My father owned 5 autobody shops we loved Zeibart it brought in alot of repairs. Even spraying old oil or a light covering of grease works far better and cheaper than Zeibart. Eastwood's or POR are two VERY GOOD products.
Forget Naval Jelly.

[A_DAB_will_do]

Nope, but lots of the folks around here have those inflatable, portable swimming pools. :p

If I see one big enough, maybe I'll ask if I can fill it with evaporust, and then dunk the flatbed in it overnight....;)

Remember the thread about electrolytic cleaning of metal parts? Know any abandoned, foreclosed homes with a swimming pool that is accessible to the truck bed??

[A_DAB_will_do]

Metalmeltr, Specter,

Thanks for mentioning Eastwood. I'd looked at their products a long time ago, but forgotten to save the website. I think I'm going to do the work myself. I'll try their rust coverter and then encapsulant.

Almost anything is better than Zeibart. If Zeibart gets cut or nick water gets under it and the coating holds it there creating more rust. Eventually then the Zeibart falls off leaving a big hole. Shops like Zeibart cause it fast and relatively easy to put on and charge the customer alot. My father owned 5 autobody shops we loved Zeibart it brought in alot of repairs. Even spraying old oil or a light covering of grease works far better and cheaper than Zeibart. Eastwood's or POR are two VERY GOOD products.
Forget Naval Jelly.

[Nitesky]

Best I have ever seen as far as preventing rust is 1 part used motor oil to 2 parts diesel fuel. Use a cheep garden sprayer and thoroughly coat everything on the underside of the vehicle. makes a mess but keeps it from rusting and its low cost.

Funny, it hasn't worked for me at all on a parts truck that hasn't been on the road since I started spraying it. Fuel oil is actually not oil at all and it allows the inside of a fuel tank to rust very easily. I found that the tinned motor oil just drips off and what is left is much too thin to do anything. The rust damage since I started spraying this old-wive's-tale is severe. Anything else has to to be better.

If the underside of the box is rusted I suspect that exhaust was or is exiting under the box.

[kburd]

diesel fuel and oil mix makes a great spray for concrete forms etc. nothing will stick with a good coat of this if applied immidatley before use. so in my opinion it is not the solution for your problem. i would take the bed off get it a good sandblasting and paint it properly with a good frame paint. Any painter will tell you that rust converters just dont work and all they do is make it look pretty on top while it is still getting whittled away underneath. if you want this truck to last that is what i would do. if you are going to move it in a year or two then make it look pretty for you and let the next guy worry about it.

[Oldiron2]

I have successfully used oxalic acid and phosphoric acid to dissolve thick rust from smaller parts, and phosphoric acid to convert thin rust layers or to 'passivate' the surface of clean steel, but agree that anything but recently-formed rust on new steel may be too thick for sprays to do much with, besides convert the surface. If any rust remains, it acts like a catalyst and causes more to form beneath it. IIRC, there's an explanation of the process in my old copy of Inorganic Chemistry by Partington.

[Donald Branscom]

To stop rust use Phosphoric acid. It turns iron oxide to iron phosphate. Rinse and then paint within 4 hours. Two part epoxy paint is best but Rust Oleum primer will last many years.

[Nitesky]

To stop rust use Phosphoric acid. It turns iron oxide to iron phosphate. Rinse and then paint within 4 hours. Two part epoxy paint is best but Rust Oleum primer will last many years.

RustOleum or not, I haven't found a primer to be much good at protecting metal from corrosion. Primer is much too porous to block moisture and it has to be that way to allow the top coat to key and thus stick.

If you get access to apply primer then you have the access to apply POR-15 and THAT stuff works.


I melted a big piece out of my Miller Elite helmet. Took and covered the wound with three layers of Duct Tape and then two layers of POR-15. It dried hard like the original plastic and made a good repair. By the time the UV gets to it I will have purchased a new shell anyway. Primer is only paint and paint is just paint but POR-15 is amazing.

[Ken Dennis]

Have you ever noticed the spot right above where the U-joint is on a vehicle , after many years of it slinging grease on the underbody, that is the only place that has never rusted under there,sept maybe where an oil leaking engine has thrown oil all over the place!
Hmmm, I wonder why!

[MikeD74T]

Funny, it hasn't worked for me at all on a parts truck that hasn't been on the road since I started spraying it.
Fuel oil is actually not oil at all and it allows the inside of a fuel tank to rust very easily.
[/LIST]I found that the tinned motor oil just drips off and what is left is much too thin to do anything. The rust damage since I started spraying this old-wive's-tale is severe. Anything else has to to be better.

If the underside of the box is rusted I suspect that exhaust was or is exiting under the box.

That explains why home heating oil tanks won't last much longer that 40 or so years ! :confused: MikeD74T

[metalmeltr]

i have read that a produt known as primer surfacer can actually hold mositure near the metal promoting rust, if you use a product called epoxy primer it can actually be mixed as a sealer by simply adding more reducer. An example of this product is ppg's dplf epoxy primer, it comes in diferent color also 40 is grey 90 is black there also a few other colors

[Nitesky]

That explains why home heating oil tanks won't last much longer that 40 or so years ! :confused: MikeD74T

The inside of the tank is a much different environment than the underside of your vehicle. Salt hardly touches the inside of the tank and the very bottom of it is protected from oxygen. It is also much thicker than truck parts. I just had one rust through and cause a $170,000.00 fuel spill cleanup @ 4-1/2 years old. It is called oil but it ain't oil and it don't act like oil.

[hp246]

I've used POR 15 . It works well for what it was designed for. but if you really want to do the job right, you need to remove the box. Blast it. Use one of the rust coverters. Then use something like POR 15 or Rust Bullet.

I tried Rustoleum. It is garbage. It peels off after about 6 months.

If you don't want to put the work into it to do the job right, then mix motor oil and fuel oil and spray the crap out of it every 6 months.

[A_DAB_will_do]

HP246,

Thanks, I've gotten a number for someone who does sandblasting on the side. As soon as I have enough spare cash, I'm going to get the bed and frame cleaned up and then do it right. Might be this summer or next...The rust isn't bad yet, and I'm hoping to get enough money together to take care of it before the truck sees another winter...But a set of 4 new rear tires has to come first...

[denrep]

I've gotten a number for someone who does sandblasting...
I'm going to get the bed and frame cleaned up and then do it right. Might be this summer or next...

Meanwhile, you could oil it at minimal cost.
In fact, why not oil one side and leave the other side natural?
I think the results will speak for themselves, about the effectiveness of underbody oil treatment.

From watching the condition of the old oil-leakers, it was obvious that oiling was an effective underbody rust preventative. To test the oil theory, I once oiled half of a new truck cab, and left the other side natural. On the test cab, the oiled side stayed in rust-free condition, as the untreated side slowly rotted away. For me there is no doubt that underbody oiling works.

I recently inadvertently rust-proofed a car, when two gallon oil containers split and spilled their contents in the trunk. :laugh:

The problem with sand blasting a truck body is that it removes the paint from, -and drives sand into- inaccessible areas which are then impossible to clean or paint. The sand pockets can block paint from reaching the metal, and hold moisture, thus giving new rust an ideal start.

Good Luck

[denrep]

I was lounging around under an old car, when this thread came to mind:

33507

33508

In the areas of the car that received a generous treatment of leaking oil; preserved under the oily coating, I could see the 85 year old original paint!

Good Luck

[A_DAB_will_do]

Cool pics Denrep, thanks. If the bed were in good condition, I'd go with oiling it. But it's already rusted, and I'd like to clean that up some before I try applying any kind of rust preventative. I'm loath to crawl under there with wire brushes and a grinder with wire wheels/cups, and clean it up by hand.

Maybe I'll talk with the guy doing the sand blasting and just have him work on the underside of the bed, leaving the truck frame alone. The frame is in better shape than the bed. There's also little or no places to trap the blast media on the underside of the bed.....

[farmersamm]

That thing got mechanical brakes????

Pup looks like it's hydraulic all the way around, maybe even disc:laugh: Anti sway provided by a wagging tail:jester:

[farmersamm]

And who on God's Green Earth "lounges" around under a car??:laugh::laugh:

Been caught doin' that a time or two. Lookin' at the world from a different perspective:cool:

[baldy347]

Air Preheater div. of Alstom Power now uses raw veggie oil for rust prevention because after a year of testing on Vertical surfaces [out in the open at that] full sun ,rain and snow, plain old salad oil outlasted all the rest. The cheaper it was the better it stayed.! this included commercially prepared industrial preseritives[sp?]

[brendonv]

Amsoil makes a product called Heavy Duty Metal Protector. I recently bought a couple cans and the stuff is great. I sprayed it on my under carriage of my truck and the water beads up like a fresh coat of wax.