Will naming John Doe defendant protect statute of limitations?

I’m have to file suit in a day or so to protect statute of limitations and have a defendant that I can’t yet identify. Does naming a John Doe defendant protect the statute of limitations?

Answer: I’m not sure suing the John Doe defendant protects the statute of limitations. The problem is you must have given notice to the correct defendant within the Statute of limitation but just misnamed them. Unless you have some way of showing that the John Doe corporation you ultimately identify had notice of the suit within the SOL, I don't think it does you any good.
Attached is a pretty comprehensive brief on the relation back issue. At the time it was written, the courts were paying a lot of attention to whose fault it was that the defendant was misnamed. The U.S. Supreme Court has since changed that in Krupski v. Costa Crociere S. p. A., 560 U.S. _, 130 S.Ct. 2485, 2490, 177 L.Ed.2d 48 (2010) where the Court said: "We hold that relation back under Rule 15(c)(1)(C) depends on what the party to be added knew or should have known, not on the amending party's knowledge or its timeliness in seeking to amend the pleading."