I have four general questions on engine maintenance and troubleshooting that I would like to air, and if they have been discussed to death before, then kindly point me in the right direction and I will do more online research.
Q1. I have heard a general rule is Oil changes are recommended every 50 hours of operation or yearly. If you run the engine just to get in and out of the marina, say for 45 minutes each way, about 12 times a year, ( I know, I need to sail more ), is it best to change the oil yearly, or is at 50 hours sufficient?
Usually, it is EVERY 100 HOURS, not 50 or EVERY YEAR, which ever is less...If you only motor 10 hours a year, you want to change your oil at least ONCE A YEAR. Used motor oil is very nasty stuff, and replacing it on a regular basis is good for your engine.
Q2. I am smelling a odor of diesel fuel in the cabin when the engine runs getting my sailboat in and out of the marina, and I see no visible evidence of a leak, so other than following the path of the fuel lines, any other places to check? Would an exhaust leak also smell like a diesel fuel leak or is it likely I have a loose hose clamp, bad hose, leaking fuel pump, etc. Any troubleshooting tips would be good.
It could also be the smell of unburnt fuel coming in with the exhaust fumes. Clean the engine off very thoroughly, and then run it... and check to see if there is any visible fuel that appears.
It would help if you said what make/model engine and what kind of boat you have, since there may be something specific to the engine/boat that is commonly causing this issue. BTW, I see you said that the engine is a Yanmar 2QM15 in your next question.
Q3. When I start the engine, I notice it takes about 2 minutes for my tachometer to start registering rpm readings. Not sure if the sender on the motor is acting up, or if the dial on the panel is. Other than a visual inspection for coorosion, loose wires, etc, what is the best way to tackle this? Just get out the multimeter and start tracing voltages around? My engine is a 1980 2QM15 that may need an overhaul on some system components.
The tachometer generally runs off of a contact on the alternator. Check the connections there first.
Q4. Speaking of overhauls, my 2QM15 runs great, starts up great, but has about 900+ hours on it. Any thoughts on when it is time to have it seriously checked out? Is just wirebrushing rust off, and doing touch up paint sufficient to keep it in good shape? At what point do you need to tear into exhaust elbows, etc. I replace the water pump impellar and engine anodes, so don't think I totally neglect the engine, but at what point does rust on the exhaust header = replacing the exhaust header? Do people actually replace the engine wire harness or sensors somewhere along the way?
Keeping the engine paint in good shape goes a long way to protecting the engine from rusting out externally. Keeping the anodes in good shape will protect it from galvanic corrosion.
However, I'd point out that if it ain't broke, fixing it might cause more problems than it solves.