Rust kills more of our trucks than any other cause. This ~$100 investment (depending what you own already) can save thousands in body and frame rot and struggling with seized bolts, and keep more of the cars and trucks we love on the road. I've used bar and chain oil for years and a knowledgeable friend has used B&C and Fluid Film and has said they're comparable. Both work OK but need annual reapplication and anything that is exposed to constant road spray like the A arms is bare in a matter of weeks. This treatment will not wash off easily, or maybe ever. For most of the vehicle areas it seems like this will be a lifetime coating. It's a PITA, but worth it.
Ingredients -
2 gallons name brand bar and chain oil ( all season, or 1 gal winter, 1 summer)
16 oz paraffin wax
Spray gun with wands ( I like PMT's - https://www.amazon.com/Undercoating-Gun-Spray-Wand-Kit/dp/B018RI373S/ )
Air compressor, 4CFM or higher, 8+ is ideal
Metal paint can
Propane/MAP torch
Scale
Hatchet
Hot plate
Old shirt
Duct tape
Optional:
Infrared thermometer ($17 @ Amazon.com )
Spray suit (the heavy duty plastic lined one from Home Depot paint section works very well)
Spray sock (for hair, paint section)
Truck/car should be clean and dry underneath.
The ratio of wax to oil makes a big difference. You don't want to go above 2 ounces per quart or the oil will harden at very high temperatures, making spraying difficult, as well as possible chipping at cold temperatures. I put various concentrations on wax paper and put it in the freezer, at 0* anything much above 2oz/qt would separate from the paper rather than bending with it. 2oz/qt begins to harden around 150*. Much below 1 oz/qt would make the mixture more fluid than ideal, this mixture hardens around 100*. I used 2 oz/qt on high splash areas like A arms and low crossmembers, as well as anything I could access easily without a wand. With a wand 2oz concentration tends to harden by the time it reaches the end, but can still work with enough heat.
Wrap spray gun base with an old shirt and duct tape to keep the oil warm, like this:
Put paint can on hotplate, add oil, and turn on high. Oil will begin to lightly smoke around 150* and heavy smoke around 200*, this is too hot for the washer in the spray gun so keep it under 200*. Chip up wax into quicker melting flakes, if you don't have a fine scale weigh a large block and divy it up, then chip it. Add to oil at desired ratio, probably start with 2 oz/qt. When mix hits about 175* and wax is all melted add to gun. Beware the vent hole, don't spill this on yourself! You will have to jump start the top of the gun or wax will harden when it hits this, apply heat from torch to top of gun, from base to tip, both sides, then spray away. The threaded nozzles affect flow rate so play around with that till you find one that works for you.
Anytime you stop spraying long enough for the gun to cool down you will have to reapply heat from the torch to it, especially with the higher wax mix. When using nozzles, especially the long one, you will have to heat them with the torch as well, going quickly and careful not to melt them of course. This is an extra PITA but is an important step to get inside of the frame. Take your time and get inside all holes you can find, in A arms, crossmembers, top of the shocks, etc. I dropped all front skid plates, gas tank skid plate, and spare tire to spray everything. Try not to get anything on the exhaust, especially the catalytic converters. It's a good idea to keep a fire extinguisher in your vehicle at all times, but especially for the first few trips after undercoating.
I applied inside of the doors (salt spray will run down the windows and inside in the winter and rust them from inside) by drilling a 1/2" hole at latch side, spraying with the lower wax mixture, and plugging with these - Amazon.com . I also did inside the rockers.
This is what my GX A arms look like two months after spraying and constantly subjected to NH salt and slush.:
Fully waterproof. You can still see runs on the crossmembers.
