How to Troubleshoot Inboard Motors

Inboard engines are more aestetically pleasing and hard to get to.

Owning a boat is mostly enjoyment with some headaches thrown in, especially if the engine isn't running smoothly. Marine elements often can lead to problems with an inboard or outboard motor, more so than an automobile engine, which at least is kept dry under a hood. Learn how to troubleshoot your inboard engine and perform regular maintenance, and you could avoid making some costly repairs or replacing parts that were fine from the start.

Things You'll Need

• Garden hose marine motor attachment
• Marine tool kit with screwdriver set, socket set, multimeter, flashlight, spark plug tester and compression tester

Instructions

1. Check your fluid levels. This should be the first thing you check when troubleshooting. Make sure the oil level, especially, is full and the oil isn't dirty by inspecting the dipstick.

2. Examine the exterior of the engine for loose or frayed belts and hoses. Also check to see that all bolts and other connections haven't vibrated loose. Often an inboard engine's mount can loosen. Tighten these and any other bolts when required. Inspect the fuel line from the fuel pump to the engine for frayed tubing or loose connections.

3. Turn the boat on, after putting it in the water. Attach your hose adapter to its drainage plug at the bottom of the engine, then attach a garden hose to the adapter.

   Turn the key. If the motor starts fairly quickly, you can eliminate most battery or ignition issues. Give it some throttle. If it revs accordingly, eliminate throttle issues too.

4. Turn on your multimeter and place its positive and negative tongs on the alternator ports. Check your engine manual for placement. It should read 14 or more.

5. Turn the engine off and disconnect your hose adapter. Remove the spark plugs with the appropriately sized socket. Install your compression tester in one of the plug cylinders, then turn over the engine just shy of starting up. The average reading is 115 to 125 lbs., but you should check your engine manual to confirm since some compression readings are higher. Lower than 115 lbs., however, indicates the potential need to replace either the piston, head gasket or cylinder.

6. Attach a spark plug tester to all leads, after making sure you've removed all plugs. Turn the engine key but not all the way on. A blue spark should appear when the key is engaged.

7. Get a tune-up if your boat is powering on and working but exhibiting wear. A fluid swap, new rotor or set of spark plugs can go a long way toward extending your inboard engine's life. Replace spark plugs with the same brand to ensure continuity.

Tips & Warnings

• See a trusted mechanic if you can't find your motor's problem. He can hook your engine up to a diagnostic machine that can easily pinpoint problem parts.

References

• Blue Water Marine Services: Inboard Motor Troubleshooting