I got this answer from a retired 767 captain.
My question is relating to a B737.
"About 30 or so minutes before flight the copilot preflights the aircraft. He may catch a problem at that time (such as a fuel or hydraulic leak, a bad slat, etc.). About 10 minutes prior to push back the pilots run the check lists(challenge and response), then the before start check list. Anywhere along the line a problem might occur. Depending on the seriousness of the problem, a delay might occur, or possibly cancelling the flight. The problem is written into the ships log book. Then it`s up to the mantainence department to correct the problem and enter a write up in the same log book as to what corrective action was taken.
Some items are minor, and can be corrected at a later time. These are "MCOed"(Maintainence Carry Overs), a small sticker is placed on the affected item and another is placed inside the aircraft log book. Pilots are not allowed to fix anything, even change a light bulb. Hope this answers your question."
Em, another question: If there is a problem (engine, structural etc,) where does the pilot log it? Are there separate logs for engines and also are the logs carried on the aircraft or kept with maintenance or where?