Diy rust proofing a 2017 Prius prime

I live in Maine.

I have a buddy who runs an automobile repair shop, he offers lanolin-based undercoatings. He has a lot of customers and they seem to love the undercoatings.

My concern though is the plastic bodywork. On my 2011 Prius I have seen how the body has become very fragile and brittle. The grommets that hold body pieces in place, pop loose. My 2017 is following the same pattern. I am far more concerned about the quarter-panels popping loose, than I am about undercarriage rust.

 

I use these stainless steel neoprene washers to keep the steel bolt heads from wearing into ans degrading the plastic panels where they are fastened.

1/4” x 1” OD Stainless EPDM Washers, (50 pc) Neoprene Backed, Choose Size & Qty, by Bolt Dropper

Expensive, but I love my Quickjack lift, when I need full access to the underside of the car. Got it in 2017 for $1,000 delivered Black Friday Special.

 

Wow, that's a lot of work for preparation. I brought in my then-new 2017 PP to a shop that applies Fluid-Film undercoating. The tech at the shop looked at the underbody of my PP and told me that there is nothing they can spray onto unless all the plastic shields are removed first. That meant extra labor cost, and the annual application of this stuff would get way too expensive. I decided not to bother with it. It was a good thing I did not spend extra cost on the car. I did not keep the car long, but when I sold it two full winters later, the rust on my car was similar or worse than what is on yours now. Mostly surface rust, but still very prominent rust developing around brakes and suspensions. Since then, I have used aerosol spray WoolWax or variants to spray on the areas accessible when the tires needed to come off for the winter. But, if I decide to do the entire underbody, I will likely leave the job to professionals.

A few years later, I purchased a used Nissan Pathfinder which had been on NE winter road for 5 years. The underbody had a quite bit of surface rust. I decided to take it to a shop to have it sprayed, but this time at a shop that uses Wool Wax. See the photo of before and after.

Do you need underbody rust protection on new Prime? | Page 5 | PriusChat

It has been two years. Here is the pic I just took. Where it was applied, it is holding very well. But I think I am going to bring it back for re-application soon.

 

Yes, I had my Gen3 Prius treated with FluidFilm at a shop when new. Gen3 had fewer underbody covers than Gen4 and they did it without taking off the covers. Then when I took my first PP back to the same shop, the tech told me that it really can't be sprayed without taking off those covers. When we bought the used PathHy, I brought it to the same shop for FluidFilm, but they had stopped offering the service and referred me to another shop doing a similar service nearby. The shop offered only black color WoolWax. It does effectively cover already rusted metal and hides them. So I really can't see the condition underneath the layer of black WoolWax without first wiping it off. Since I did not remove or convert the rust before applying the WoolWax, I am sure the rust is still there. The question is, is it worse or the same as before?

I do think rust inhibitor to be effective, it really needs to be applied before the first sign of rust, preferably when the car is new. I just did spray rust inhibitors on my 5 mo old 2021 PP while wheels were off, only to the areas around the wheel well. Did not crawl under the car nor took off any of the underbody covers. I really like the way the CRC rust inhibitor went on the surface and covered it. It is by far the easiest and cleanest application compared to the other three products (FluidFilm, WoolWax, and LPS3) I have used so far.
Do you need underbody rust protection on new Prime? | Page 8 | PriusChat

Here is an example of what the FluidFilm application looked like on my 2017PP from an aerosol can. I don't have a photo, but WoolWax aerosol application was worse looking than this FluidFilm with thicker "blobs". I think doing this in the middle of summer when the temp is high, and using the spray gun with an air compressor as you have done would have made it much easier application and neater results.

 

I fell into this strategy, not by plan, just happenstance, but in hindsight it's maybe not a bad approach:

Drive the car for a while, say one winter minimum. Then, in warm/dry weather, jack up one end at a time, and see where rust is forming. Remove plastic panels as needed, as long as it's not too complicated. Apply undercoating locally where you're seeing rust, and go beyond some too, especially if it's easy. Oil soak all the removed bolts/nuts/screws (typically on plastic underpanels) before reinstalling

I've done this a couple of times now, using boiled linseed oil, applied with a disposable foam brush or old tooth brush (and an ancient can of 3-in-1 oil for the bolts/nuts/screws). It's holding up quite good. I'll revisit sometimes, especially if I notice a new, previously untreated area starting to get some rust.

There's a member here from Finland: every time he posted one of his rust horror stories, I'd take a look at ours and ayup, starting to get a bit there, better hit it with a little linseed oil.

 

Marine grade (now called "Mariner's Choice") Never-Seez is my choice for rust proofing threaded fasteners. It is a high quality industrial anti-seize with corrosion inhibitors.
Industrial Supply Group - Your Solution to Anti Seize, Lubricant and Epoxy Needs!
If any of the fasteners have a torque spec, then the spec must be changed due to the lubrication on the threads. A torque spec actually combines the twist in the fastener and the friction on the threads and bolt or nut face. Lubricate and the friction factor changes. Failure to lower the torque spec can result in stretched or broken fasteners.
https://www.antiseize.com/PDFs/torque_specifications.pdf

I'm sure glad I live in a place that rarely uses salt on the roads.

 

Good job. I am debating what to do with my PP this year. Last year, I sprayed CRC Marine rust inhibitor spray can on one side and LPS3 corrosion inhibitor spray on the other side, just the areas I can spay while the wheels were off without crawling under the car. Both sides held up pretty well, but there were still some areas with surface rust. Not exactly sure if that's because I missed spraying the area or if the inhibitor did not prevent the rusting. I really don't think I will be keeping the car long enough to see the benefit of rust-proofing.