Boat engine won't start: find the cause and help yourself safely

Outboard (petrol): what to check

1. Check that the kill cord clip sits properly on the emergency stop switch. Without it the engine will not start.
2. Put the gear lever exactly in neutral. Most engines with remote controls only start there.
3. Switch the battery isolator on.
4. A single click often means a weak battery. Check the terminals are tight and free of white or green deposits. A charged 12 volt lead acid battery at rest reads about 12.6 volts on a meter; well below 12 volts there is often not enough power to start.
5. Many smaller outboards can be started with the pull cord or an emergency rope on the flywheel. The manual shows how.
6. Look at the fuse or breaker for the starting circuit if your engine has one.

Inboard (diesel): what to check

1. Check the emergency stop and the stop button at the helm. If an emergency stop is pressed or a kill cord is off, the engine will not start.
2. Gear lever in neutral.
3. Switch on the isolator for the starter battery. With a parallel or emergency start switch, the house battery can help when the starter battery is weak.
4. Terminals tight and clean? Measure the voltage as for the outboard.
5. Jump start from a second battery as you would a car: positive to positive first, then negative of the good battery to an earth point on the engine of the boat that will not start. Disconnect in reverse order. With lithium batteries follow the maker's instructions only.
6. Check fuses and breakers on the engine panel.

Outboard (petrol): what to check

1. Check the kill cord clip: on many outboards the starter still turns without it, but there is no ignition.
2. Is there petrol in the tank? Open the fuel valve and the vent screw on the tank cap.
3. Are the hose connectors at tank and engine fully clicked in? Squeeze the primer bulb until it is firm.
4. Cold engine: use the choke or cold start aid as the manual describes. A warm engine usually does not need it.
5. A strong smell of petrol at the engine suggests it is flooded. Wait a few minutes and start again as the manual describes.
6. Look at the filter bowl or water separator. If there is water in it, drain it if you know how.

Inboard (diesel): what to check

1. Check the fuel gauge and fuel valve. With several tanks: is the right one selected?
2. Preheat in cold weather if your engine has glow plugs.
3. Check the water separator or pre filter: drain water from the bottom of the bowl, change a clogged filter if you carry a spare.
4. If the tank ran dry or a filter was changed, there is air in the system and the diesel has to be bled, usually with the hand primer on the lift pump and the bleed screws, exactly as the manual says.
5. Crank for a few seconds at a time only and let the starter rest in between. The manual gives the time.
6. Boats with a wet exhaust: long cranking without the engine firing can push seawater into the engine. After several failed attempts close the seacock, and be sure to open it again before the next start.

Outboard (petrol): what to check

1. Open the vent screw on the tank cap. If the primer bulb goes soft or flat while running, that points to vacuum or a blocked line.
2. Check the hose for kinks and squeeze the primer bulb again until firm.
3. Push the kill cord clip firmly back on.
4. Return the choke once the engine is warm, if it has one.
5. Look for water or dirt in the filter bowl.
6. If the engine dies under load, a line may be wrapped round the propeller. Engine off, kill cord off, tilt up and look.

Inboard (diesel): what to check

1. Check the fuel level: with little diesel in the tank, the pickup easily draws air in a swell.
2. Inspect the pre filter and water separator, drain any water.
3. Fit a spare filter if you carry one, then bleed the system as the manual describes.
4. If the engine stalls when you engage gear, something may be caught in the propeller. Engine off, gear in neutral, only then take a look. Only go into the water if you are secured and confident.

Outboard (petrol): what to check

1. Throttle back to idle. With an oil or temperature alarm, stop the engine.
2. Check the tell tale: if no water is coming out of the engine housing, go to the case "Engine overheats".
3. Four stroke: after a few minutes check the oil on the dipstick.
4. Two stroke with an oil tank: check the oil level in the tank.
5. If the alarm returns after a restart, only motor as far as you really must.

Inboard (diesel): what to check

1. Throttle back to neutral. With an oil pressure or temperature alarm, stop the engine at once.
2. Check the oil on the dipstick once the engine has stood for a few minutes.
3. Temperature alarm: go to the case "Engine overheats".
4. If the charging light is on, look at the drive belt. On many engines it also drives the cooling water pump. If it has snapped, engine off.
5. If the alternator is not charging but the engine stays cool, save power and head for the nearest harbour.

Outboard (petrol): what to check

1. Stop the engine. For reference: while the engine runs, a thin jet of water comes out of a small hole in the housing, the tell tale. If it is missing, no cooling water is flowing.
2. Tilt the engine up and clear the water intake grilles on the lower unit, for instance of weed or a bag.
3. Sometimes only the tell tale hole is blocked. Clear it carefully with a thin wire or cable tie.
4. If there is still no jet after a restart, the impeller is often worn. On an outboard that is usually a workshop job.
5. Only carry on when the jet is strong again and no warning is showing, and then slowly.

Inboard (diesel): what to check

1. Stop the engine. Is the seacock open?
2. Inspect and clean the raw water strainer. Close the seacock first and open it again afterwards.
3. Check the drive belt.
4. Impeller: if you know how and carry a spare, change it with the engine cold as the manual describes. Find any missing vanes, otherwise they lodge in the heat exchanger.
5. Freshwater cooled engines: never open the header tank cap while the engine is hot. Let it cool, then check the level.
6. If water comes out of the exhaust again after starting and the temperature drops, head slowly back to harbour.

Outboard (petrol): what to check

1. Smoke under the cowling or a burning smell: engine off, fuel valve closed, fire extinguisher ready.
2. Dense white smoke and no tell tale: go to the case "Engine overheats".
3. Two stroke on premix: a little blue smoke is normal. A lot may mean too much oil in the mix; the right ratio is in the manual.
4. Black smoke at full throttle: ease off and at the next opportunity check the propeller for fouling, lines and damage.

Inboard (diesel): what to check

1. Smoke from the engine bay: engine off, close the fuel supply if it is safe to do so, main switch off. Do not open the engine hatch wide, a fire would get air. Extinguisher ready, lifejackets on.
2. White smoke with little or no water from the exhaust: check the cooling as in "Engine overheats".
3. Blue smoke: check the oil level. If it persists, the engine needs a mechanic.
4. Black smoke: reduce revs, check the air filter, check the propeller for fouling or a line.