Re: Water in engine oil
Well, the plugs can tell you which cylinder it is. Water can do some crazy things. It can break electrodes off and cause insulators to go AWOL. No matter what, it'll look different. Hopefully you'll just have a discolored plug then it's not too serious.
I check the plugs for several reasons:
It'll tell you what head to pull.
If the spark plug is severely damaged then chances are there are messed up valves/seats and maybe a pistion top. Perhaps even a scored cylinder wall (read: expensive fix). If it's been detonating at the wrong time for a while it can cause wrist pins to become ruined.
If the plug shows little change from normal then it is, hopefully, not too bad. That means maybe as little as a head gasket or as much as a new head.