Expert: Jeff Grigg - 2/15/2008

Question
I have an 87 Mercruiser 3.0L.  It starts hard but runs OK after warming up.  After the boat is warm and I shut it off it starts very hard or not at all (normally need to have throttle wide open to get it to start.  Also, at an idle of under 1,200 RPM and in gear the boat begins heating up.  No temperature problems except at the low speed.  Any help is appreciated.

Answer
Jerry with a boat of that age you must make sure the engine is in tune and "up to snuff" before diagnosing your particular problem.
Is the compression even and good? Is the ignition system in good shape? Any exhaust blockages or leakage, corrosion? What is the condition of the spark plugs and if you have them the points and distributor cap, plug wires.
Once you make sure all of these are OK you need to find the cause of the overheating. I would suspect the water pump(s) may be worn and need replacing, you have two. The drive's pump which is referred to as the raw water pump and brings water to the engine and the circulating pump. If either one is failing or not adequate you will have overheating issues. Also check your thermostat and the exhaust for blockage in the exhaust manifold.
Once up and running the force of the drive going through the water will help "push" cooling water to the engine, so I would look at the raw water pump first.
As for the hard starting you could have one or a combination of problems. You fuel pump may be weak causing you to crank the engine to fill the carb. The overheating can cause vapor lock or a percolation of the fuel in the carb. The carb can be out of adjustment having too low of a fuel level or too rich or lean.
Do a complete tune up and replace the outdrive water pump, then see what happens, your starting problem may go away.
Jeff