Simple, inexpensive protection for our MR2’s undercarriage

J.G.
Update by J.G. Pasterjak to the Toyota MR2 Turbo project car
Jan 5, 2023 | Toyota, MR2, Toyota MR2, Fertan

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So many cars in our world fit into the same category as our 1991 Toyota MR2: They’re a little crusty underneath, but not bad enough or valuable enough to warrant a bare-tub restoration.

Or the other scenario: They’re destined for a life on track, where they’ll need some protection from rocks and debris while fending off further environmental damage.

Our Toyota certainly fit into both of these categories. It lived much of its life in New Jersey, and while it had no real structural rust, there was a lot of surface rust underneath along with some crust showing on brackets and attached hardware. It needed some attention, but a full restoration was not in the time, money or interest budget.

But while we had the car apart for its V6 transplant, perhaps we could make things a little better.

[What does it take to swap a V6 into a Toyota MR2? | Full parts list]

Enter Fertan and its lineup of chassis protection chemicals. The company recommended a multi-step process where we’d clean the underside of our MR2, neutralize the surface rust and convert it to a paintable finish, and then coat the entire thing with a protective skin to guard against further corrosion and damage.

The process starts with a degreasing and pressure washing of anything that’s going to eventually be rustproofed and coated. For us, this meant removing the rear subframe and prepping it separately since we wanted it coated on all sides. Then once it was reinstalled, we could roll the car outside for an undercarriage bath.

We first cleaned everything with a thorough application of CRC Parts Cleaner and Degreaser followed by an aggressive pressure washing.

After an overnight rest, as well as some judicious compressed air to remove any pockets of moisture, we sprayed down the underside of the car with Fertan’s Rust Converter.

This product can be applied liberally to any surface, and we used a gravity feed gun set to around 45psi to get best results. It can also be applied via hand pump sprayer but will obviously take longer if you’re doing a large area.

The Rust Converter goes on with the consistency of maple syrup and sticks fairly well, even when applied overhead. Within an hour or so, it dries to a sticky, brownish coating, so overnight drips will be minimal.

After 24 hours, the coating can be hosed off. It’s highly water soluble, so a pressure washer is not needed at this stage–enough water volume to thoroughly rinse the surfaces is more important than pressure. During those 24 hours, the Rust Converter is busily working away, converting any oxidation into a paintable, zinc-coated surface.

Once the Rust Converter is rinsed away and the surface is dry, it’s ready for the coating of your choice. We allowed another 24-hour break, as well as lots of pressurized air to clean out the crevices of water, before we applied the final layer, a protective layer of Fertan’s Stoneguard.

Stoneguard is one of those products that actually exceeded our expectations for both ease of use and results. It’s not quite like undercoating, and not quite like truck bed liner, but definitely exists in the same family.

The resultant coating is thinner and harder than those materials, but also feels and performs like it has excellent protective qualities. Applied from a spray gun or a can–we recommend getting both if you plan to do a large area as the gun is perfect for delivering large volumes while the can is better for reaching into tight places–the resultant finish has just enough texture to appear protective, but not so much where it looks like a rubberized coating.

The product also sprays on very “dry” and adheres to the surface on first contact. There’s almost no overspray, and no “clouds” of product lingering around. Proper respiratory and eye protection is still recommended, but we had to do a bare minimum of masking because the application was so easy to control.

The thinner-than-undercoating application also makes it easy when you decide to just spray right over existing fasteners. Where a thick coating of undercoat or bedliner can render a bolt head unusable, the Fertan Stoneguard is thin enough to leave fasteners fully functional while still providing a high level of protection.

Ultimately, we coated our entire undercarriage, wheel wells, and as much chassis as we could reach.

The final tally to treat our MR2: not quite a quart bottle of Rust Converter ($39.95), the entire liter of Stoneguard ($24.95) and maybe a third of a can of the same ($14.95).

That’s less than a hundred dollars to turn a slightly ratty-looking former Northern car into something that not only looks good but is well-protected. For a small, not-too-rusty car like our MR2, we’d probably recommend two liters each of Rust Converter and Stoneguard, plus a spray can of Stoneguard. That would be enough for an initial treatment, plus another season or more of touchups, retreatments, and coating of any replacement parts that may come along.

With our chassis now cleaned and protected, we’re deep into the reassembly phase with our MR2. Pretty soon, we’ll be sliding out 2GR-FE V6 into place and enjoying nearly 300 wheel horsepower–all without worrying about all those rocks we’re kicking up doing any damage to our chassis.

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Comments
matthewmcl
matthewmcl Dork
1/4/23 1:45 p.m.

I was not planning on doing anything like this. I am now planning on doing this. Thanks for the write-up.

JG Pasterjak
JG Pasterjak Production/Art Director
1/4/23 2:45 p.m.
matthewmcl said:

I was not planning on doing anything like this. I am now planning on doing this. Thanks for the write-up.

Yeah, same. There are few things I hate worse than anything to do with a paint gun. But this stuff is so easy to work with and the results are so instant and positive it actually made the process fun. 

NorseDave
NorseDave HalfDork
1/4/23 5:46 p.m.

Hmm, that looks really good.

AnthonyGS (Forum Supporter)
AnthonyGS (Forum Supporter) UberDork
1/4/23 10:05 p.m.

Awesome!  I'm going to need to do something similar with my Subaru soon. 

Colin Wood
Colin Wood Associate Editor
1/5/23 2:37 p.m.

Any product that elicits both a "so easy anyone can do it" and a "why didn't I do this sooner" reaction goes on my short list of things to buy.

Olemiss540
Olemiss540 HalfDork
1/5/23 3:51 p.m.

How does the stoneguard compare to Por15? Process for both seems similar.

JG Pasterjak
JG Pasterjak Production/Art Director
1/5/23 5:07 p.m.
Olemiss540 said:

How does the stoneguard compare to Por15? Process for both seems similar.

POR15 is a single step, this is a two-step. I prefer the finish of the Fertan stuff to POR15. It cures more evenly with no streaks, and I like that it has some texture. I'd wager it's also more protective, although only time is going to be the judge of that.

Really the biggest difference for me was how easy this stuff was to use. I would have zero fear about putting the car up on the lift and doing some touchups with no drop cloth or no masking or anything. POR15 is not nearly as forgiving. 

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
1/5/23 5:29 p.m.

I think POR-15 is two step if you really want to do it right - you should hit it with phosphoric acid first. POR gives it a different name but that's what it is. It's a good choice for things like roll bars and a Locost chassis, but this sounds like a better choice for an undercoat refresh.

Olemiss540
Olemiss540 HalfDork
1/5/23 6:19 p.m.
Keith Tanner said:

I think POR-15 is two step if you really want to do it right - you should hit it with phosphoric acid first. POR gives it a different name but that's what it is. It's a good choice for things like roll bars and a Locost chassis, but this sounds like a better choice for an undercoat refresh.

This is a 3 step (decrease, rust convert, paint) exactly like POR 15 unless I missed something.

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