[smayst824]

A friend of mine is looking to buy a 2017 Subaru Legacy and asked me for advice. The car is a good deal, low miles, and is certified, so long powertrain warranty (hey, flat-6 motor, so it's kind of relevant here!). But he sent me amphoto from the underside that concerns me. This car's in-service date is 11.29.2016, but it already has some rust on the frame underneath. Carfax says it's a Maryland car, and it's not like there's a ton of snow here (though we do pre-treat a LOT!).

I know Subarus have a reputation for rusting, and I wanted to show the group here this photo... please let me know if you think this appears to be surface rust that isn't a problem, or if it looks like the beginnings of rusting through and he's going to replace parts in the near future. If it's too hard to tell from this photo, please let me know that as well. Thanks for your help and expertise.

[Chopper Dropper]

It will probably leak oil in a while and coat the underneath nicely

[cmartin]

looks like nothing to me. poke it with a screwdriver or hit it with a hammer, that'll tell you

[HoodPin]

^ X2.

Surface rust is harmless. Cover it with Rustoleum or POR15 (better) and its good to go. If you can flake off or penetrate into the rust, different (worse) problem.

[Dandelion]

No concerns here. As others say - surface rust.

[jerome951]

Yep, looks like surface rust on the welds. I wouldn't shy away from the car just for that. Easy to treat as mentioned above.

For some reason it seems Japanese manufacturers are either oblivious or ambivalent about rust, even the cars assembled in Japan. My truck even had a recall due to rusty frame issues. It had surface rust on the welds 2 weeks after it was manufactured and hadn't even been driven...

[cmartin]

it happens. some caution if you plan to paint over it. I did a fair/ok job cleaning, prepping and painting my rusting chebby. Then one day I realized my paint was just a covering for the rust, lots of rust. You really need to get the rust off and prep it will a magic derusting elixir before you paint. Even then it never sleeps.

[Roo]

Appears as though road debris initiated the surface rust.
I've had a 2008 since new, virtually no rust, all underside from road debris contact and easily repairable with a good coating of Rustoleum or POR-15 as HoodPin noted.
And leaks? At 186,000 miles, with regular servicing by me, no drips of anything.
Best car I've ever had....

[Vicegrip]

Magnesium chloride getting to work. Gets into seams and joints and bonds tightly. Draws moisture from the air and causes corrosion. This “surface rust” is visual proof of incomplete rust proofing. The chemical reaction starts in areas where rust inhibiting coatings are compromised and then runs under the proofing.

Old school zinc based coatings would re galvanize scratches and heal themselves. Full dip electrostatic coatings are uneven on some textures and is often lacking on complex surfaces such as welds. Unlike spray it goes into seams but has it weaknesses. Lesser modern systems are just not up to the power of mag chloride.

[smayst824]

Thanks, all! I let him know it's not an issue and passed on the Rust-o-leum advice for if he buys it. Makes sense that the anti-corrosion coating would have a harder time in the corners by the welds.