Surface rust (unless it's on an exterior painted body surface) is not going to be covered by warranty. Unless the rust bubbles through the paint in 7 years (and under 100K miles), it's not going to be covered.
If you read the warranty, it even says rust due to salt is not covered. The warranty also doesn't mention rust of structural components.
MITSUBISHI 7-YEAR/100,000-MILE ANTI-CORROSION/PERFORATION LIMITED WARRANTY
Covers perforation (metal rust-through) in outer body sheet metal panels due to corrosion during normal use for 7 years or 100,000 miles for every new Mitsubishi, including Lancer Evolution, Ralliart and i-MiEV models. Coverage excludes corrosion due to accidents, damage, abuse, abnormal use, vehicle alterations or
contact with corrosive material such as sand,
salt, hail, stones, chemicals, acids or fertilizers.
Bottom Line:
These cars will develop surface rust fairly quickly in northern climates where salt is used on the roads...but it's up to the owner to stop surface rust of underbody areas and inside body panels.
Do any of you guys in the south with a 2014/2015 have rust on the bottoms of the doors yet?
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View my fuel log 2015 Mirage ES 1.2 manual: 52.2 mpg (US) ... 22.2 km/L ... 4.5 L/100 km ... 62.6 mpg (Imp)