I think there is a way to check your cluster, I'd have to google it. You either have a dead idiot gauge or the temp sensor in the lower left front (the car's left front) of the intake manifold is dead. Its like a $10 part and takes about 2 minutes to replace. Pull the wire off, ratchet it out, put a new one in with a light coating of high temp rtv, let it set and gtg. Also check that wire to make sure it didn't fall off or isn't cracked or corroded or cut or anything.