Will an outboard run with both cylinders cracked? I have a 1982 Mariner 25hp that was given to me. At the time it had a cracked water jacket that I repaired and then had to replace the water pump and impeller! Finally got it running this weekend and on the muffs it runs great but when it is immersed in water it runs but really lacks power! I pulled the plugs and both cylinders have water in them! I am wondering if when the water jacket cracked ( which I assume was water inside that froze!) could both cylinder walls have cracked and if so would it still run? I know that it could also be the water jacket gasket or the exhaust gasket (which looks like there might have been some leakage around it as it looks like there might be some rusty crud around it but no sign of water that I can see) I haven't been able to do a compression test yet as I don't have a tester but am gonna try to get one!