Friend gave me a 1983 Rx7 because it wasn't running. He said that he was driving it and it backfired really hard, so he drove it stright home. The next morning he went out to look at it and he took out one of the sparkplugs and radiator fluid gushed out. What happened?

 

Water Seal, the motor needs rebuilt.

 

When rotaries overheat, the aluminum rotor housings expand disproportionately to the cast iron side and center housings, which causes the rotor housings to "crush" against the tension bolts. Then when the motor cools off, the rotor housings contract and the water seal fails. Usually, the rotor housings are ruined in that case.