If you think it’s hot outdoors, go to the Belfast Maskers’ new production of “Pump Boys and Dinettes,” which opened with a big fat “yahoo” Tuesday at the Railroad Theater in Belfast.

“Pump Boys,” which often gets called a musical but is really more of a stand-at-the-mike revue, is one of the friendliest stage events ever written. It doesn’t preach, it has no moral and it’s a hot set of music with characters that will warm your heart.

You might say “Pump Boys and Dinettes” is the musical version of a good feed — a kind of melodic grits, succotash and barbecue. Nearly 20 numbers make up the show. Much of the music is Southern rock, but there’s also blues, folk, country and western, and a smidge of bluegrass harmony.

The show was written by a team of musicians in 1981. It began its career off-off-Broadway, moved to off-Broadway and then had 573 performances on Broadway. The size of the cast can vary, but it requires six talented musician-vocalists who can also doof-it-up in a playful kind of way. There’s no plot or drama, but there’s a lot of mugging, and it takes a special kind of person to do that well.

Directors Ruth Gelsinger and Tracy Lord, with technical guy Kip Brundage, have organized a seven-member cast of right-mighty singers who aren’t afraid to have fun. They bop and hop and riff their way in their beloved workplace, somewhere between Frog Level and Smyrna on Highway 57 in a down-home diner called the Double Cupp, which is run by the sisters Rhetta and Prudie Cupp (Alison Manion and Meg Nickerson).

In addition to being the targets of the sisters’ attentions, the boys at the diner run the auto shop. The performers — John Gelsinger, Russ Lloyd, Mike Nickerson, Dan Quinlan and Tony Shay — give new meaning to the term “garage band.” These guys rock, and there’s no stopping them once they take off. The women accompany them with heartful voices, pots and pans, rolling pins, wooden spoons and — what else? — tap shoes.

It’s not just the talent that makes this show work, however. The ensemble spirit of the cast is truly wham-bam. They could even turn up the power on some of their routines, but they create such an amusing and warm atmosphere that you can’t go wrong. If you’re lucky, maybe you’ll win a car air freshener at the nightly raffle. And if you’re smart, you’ll get yourself a slab of fresh pie at intermission.

“Pump Boys and Dinettes” is ideal for a small space such as the Railroad Theater. But there’s no question that the set, for all its feisty diner-garage kitsch, is cramped. The actors have to shimmy by one another, and sometimes run into one another. It would be nice to see them be able to cut loose more, swing their arms a bit, kick up their heels.

On preview night, the technical staff was still working out the volume balance between the band and the singers. In the first act, the music overpowered the vocals, which killed the humorous lyrics. But soon into the show, adjustments were made and, except for the occasional trailing away from mikes at the end of a musical phrase, the singing voices rightfully took the primary spot.

Jackson, one of the guys in the show, says he likes to shop at the mall because it has everything. “If they don’t have it, you don’t need it,” he assures. The same is true for this production of “Pump Boys and Dinettes.” You’ll go away wanting for nothing — except maybe an icy Ballantine.

The Belfast Maskers will present “Pump Boys and Dinettes” 8 p.m. July 23-Aug. 1 and Aug. 5-7 at the Railroad Theater in Belfast. For tickets, call 338-9668.