A Sayville institution since the 1930s, Sayville Modern Diner on Main Street was recognizable for its chrome exterior, retro sign and a menu of eggs, hash browns and Greek diner classics. Today, it houses the newly opened Koi Sushi Lounge, the restaurant that opened last week — with top to bottom updates.

“We had to make major changes, since some of the equipment was over 70 years old,” said a manager. Even as the railroad-car diner had been updated, very old items such as a box of coupons from 1946 alongside a live grenade — perhaps from World War II — were found by workers fixing a gas leak in 2012. Koi is bright and utilitarian, with booths and tables to seat about 80 diners.

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Fen Y. Ren is the new owner of the restaurant with eateries in Bridgeport, Connecticut. His menu focuses on pan-Asian appetizers like rock shrimp, tempura dishes and lettuce wraps ($5 to $10) as well as sushi appetizers such as a spicy tuna avocado bowl and spicy tuna pizza ($7 to $13).

Sushi rolls and hand rolls are a specialty, from spider rolls and eel cucumber rolls ($5 to $13) to more provocative selections like the “sexy girl” roll — with spicy blue crab, lobster salad, avocado and soy paper — or the “out of control” roll with raw yellowtail, tuna, salmon, avocado and asparagus topped with seared yellowtail, salmon and tuna, dressed with spicy mayo and eel sauce ($12 to $20). Hibachi dinners range from single-item dinners from steak to sea bass, as well as steak and seafood combinations ($14 to $39). All hibachi items are served with soup, salad, shrimp, vegetables and rice.

Koi Sushi Lounge is open from noon to 10 p.m. Monday to Thursday, noon to 11 p.m. Friday, 1 to 11 p.m. Saturday and 2 to 10 p.m. Sunday.

136 Main St., Sayville; 631-563-0777, koisushiny.com