Bar Oil Undercoating

by Don Martin

Here's my Vermont two cents worth on undercoating:

Spray on rubberized coatings tend to cover the rust and do nothing to kill it. Over time it will chip or peel and end up trapping salt and making your bus rust faster than if it had not been undercoated!
The best thing some of us up here have found is quality bar and chain oil. Do not get the cheap stuff. Agway or Husquarvarna seem to both use similar formulas. That is a mixture of phosphoric acid, oil, and paraffin. The phosphoric kills the rust. In fact the rust will turn black within a week. The oil and wax leave behind a sticky residue. This treatment also has the advantage of lubricating all joints, etc...
When looking to buy bar and chain oil, READ THE LABEL. Although it won't give you the ingredients, it should say something like: High adhesiveness, high oiliness, High Film Strength, Anti-Rust.
The best way we have found to apply the bar and chain oil is with a 3M Rocker Schutz gun and an air compressor at about 50-60 PSI. Atomizing the oil helps to make this a quick job as well as makes it possible to spray into doors, rockers, etc.
This stuff will evaporate/dry to some extent and leave a thin film behind.
I do my cars twice a year. In the fall, and also in the spring.
It's a good idea to pressure wash your ride and let it dry before undercoating. Spraying the oil on top of mud won't do much good...
I spray all sheet metal, joints etc underneath, and also spray in the rocker panels, doors, etc.
Would you rather have salt water or oil in them door seams ? Remember you'll be splashing up slush that seems to get inside all seams (this salt mix is not nice !)
Unlike the rubberized stuff that does nothing to kill rust, you get a chemical reaction from the bar oil with the metal which forms a protective oxide.
This treatment is for cars driven daily in the rust belt.
Considering the cost ($5 a gallon) this is economical. If you are judicious in applying this stuff, one gallon is all you need.

CAVEAT:
BE CAREFUL WITH ANY UNDERCOATING YOU APPLY.
DO NOT SPRAY IT ON THE EXHAUST OR ENGINE !
GIVE IT TIME TO "DRIP DRY".
YOU DON'T WANT A BURNIN' BUS.