8 Reasons Your Boat’s Engine Won’t Start and How to Fix It

"This site contains affiliate links to products. We may receive a commission for purchases made through these links."

Sometimes, the boat’s engine will not start. It doesn’t matter whether you bought the boat brand new or used, you should expect that something will go wrong.

But what causes the engine to fail, or only the starter rotates? In this in-depth article, I’ll show you the major causes, what steps you should take in order to fix it, and how to enjoy your boating ride.

Some good general points to remember:

  • A recent engine will often be less reliable than an older engine — but is regularly maintained.
  • The life of a well-maintained and well-maintained diesel engine is rated at least 7000 hours; Scheduled visits and scheduled maintenance will be the best guarantee of optimal availability.
  • A failure can always occur, but should never be due to a lack of maintenance.
  • Always have on board a maximum of spare parts (belts, turbines, filters, hoses, pipes), and the most complete tools possible, you will never have to regret it.
  • Take care to run your engine to the best of its optimum operating range recommended by the manufacturer (usually about 300 rpm).

Statistics about a boat sailing

  1. Back in 2016, the United States maritime transportation system decided to carry $1.5 trillion of cargo via the seaports of the U.S. to and from their international trading partners.

In the year 2014, the ocean economy, which includes 6 economic sectors which depend on the ocean & the Great Lakes, made a contribution of more than $352 billion to the GDP of the U.S. GDP which actually supported jobs for 3.1 million people.

  1. The total expenses on the market of recreational boating reached up to 36 billion U.S. dollars back in 2016.
  2. The boat manufacturers were expanding their capacity to meet the demand. This was done by building new plants & increasing production. This actually supports the recent data gotten from the Bureau of Economic Analysis.

It states that the manufacturing gross of U.S. output had made an increase of $6..228 Trillion during the 4th quarter of the year 2017.

  1. Americans took 141.6 million people to the water (both adults & children who are under the age of 18) to boat in 2016.  

Boats are usually made in America: 95 % of powerboats that are sold in the U.S. are actually manufactured there.

An estimate of 11.9 million registered boats is in the U.S. by 2016.  

95 percent of the boats on the water (sailboats, personal watercraft, and powerboats) in the U.S. are usually small, towable boats and under 26 ft.   

It is not only new boats that Americans buy; there is an estimate of 981,600 pre-owned boats (personal watercraft, powerboats, and sailboats) that were sold in 2016. This is an increase of 2.5 %.

Before a cruise departure

Do not fill the fuel tank with water. If unfortunately it is already done, do not start the engine before having completely drained the tank.

If you notice during navigation, stop the engine immediately and drain, the life of your injection pump depends on it.


Never open the cooling circuit filler cap just after stopping the engine, as this may expose you to serious burns, such as on a car.

Wait for it to drop the engine temperature and protect itself from possible splashes of boiling water using a heavy rag.

Touring the Propeller

Door Shut off the engine and remove the ignition key for safety; if necessary, install a crew at the front of the boat to prevent a water entry from behind.

Some preventive tips

Hold the engine block, the engine, and clean it as possible.

However, the washing of the engine under pressure is to be avoided, the starter and the alternator even marine are not designed to receive such pressure of water.

The engine must not swallow a single drop of water; wrap the air filter in a waterproof plastic bag before washing the engine.

Routine maintenance plan

Before leaving:


  • Oil and water levels motor,
  • The water filter,
  • The battery charge.

A well-charged independent motor battery is a guarantee of a successful start. Some starters pump more than 300 amps at startup.

Changing the cooling water pump impeller

A cooling pump-turbine in a sorry state this type of pump is found on each heat engine or to cool the exhaust line(s).

To do about every 500 hours of navigation it is known that the turbine of its pump is HS when the water of the “jar” no longer bubbles while the engine is running.

Their wear is caused by overheating, fouling, and abrasion due to sand or mud.

Significant risks for the integrity of the engine:

  • Pieces of rubber or neoprene come to melt and shut off the circulation of the cooling water,
  • The damaged fins no longer provide sufficient heat exchange to cool the engine.

In both cases, there is a significant probability of tightening and the engine is to change.

How to change it:

  • Remove the bolts holding the plate, being careful not to escape these bolts at the bottom of the engine block,
  • Remove the old turbine, levering each side with two screwdrivers, or pliers.
  • Put your finger in the lights to check that no piece of rubber obstructs it, but if it deteriorates, the ideal is to probe the downstream piping to be certain that a piece of rubber did not remain there stuck up.
  • Clean the entire cavity and the drive hub with a cloth,
  • Scrape the plate without using it with small-grain sandpaper.
  • If it is worn, turn it over and grease the new turbine,
  • Check its behavior by turning the drive pulley by hand the pump in the correct direction,
  • Do not forget to put the sealing gasket of the plate in its correct position (be careful, this seal is not always supplied with the turbine),
  • Replace the plate respecting the shape of the cavity.
  • Tighten the bolts ending with a cross-clamping,
  • Check that the impeller is free by manually turning the pump drive pulley,
  • If necessary re-open the valve of the circuit (history lived!) Otherwise, the turbine will burn in the quarter of an hour that follows, start-up.

Diagram explaining the correct assembly of a cooling pump-turbine – check that the pump works and creates a suction of water in the jar.


The water pump is used for cooling:

  • The engine block,
  • The engine block and the inverter.
  • The exhaust line
  • The exhaust line and the inverter.

On most rental boats, the water supply to the engine cooling system is doubled to prevent accidental clogging with algae or mud.


If the excessive heating of the motor usually triggers an alarm, for the cooling system of the exhaust line, this is not necessarily the case.

You can install a fitting equipped with this type of alarm for a hundred or so.

Usual Replacement Period

Bellows are replaced every two or three years.

Do not forget also check the collars that hold these bellows.

In navigation

An engine that propels a boat of 5 to 10 tons must be at a good temperature before asking for power.

Take the time to let it warm up for 5 minutes in slow motion, then gradually rev up to reach the cruising speed only when all temperatures are at their normal level. Count about fifteen minutes if you do not have control instruments.

The cruising speed

If a motor is given a maximum speed it should never be reached, except in case of emergency or for scrubbing operations.

A diesel engine should never exceed 80% of its maximum engine speed. This is the engine that the diesel engine can handle for several hours and where its performance is the best.

As an indication, a sailboat motor of 12 meters is about 2000 rev/min.

To avoid overheating

If you do not have an alarm check from time to time (in case of wet exhaust) if the engine cooling water is coming out of the boat’s exhaust line.

After running at a steady speed, let the engine idle for a few minutes before shutting down to avoid overheating that could no longer be dissipated by the stopped cooling system.

Regular checks

  • Make the oil level in the inverter,
  • Grease the rudder (to check every week during navigation)
  • In case of leakage on the exhaust line, use waterproof paste while waiting for better.
  • Check the anchor fuse holder, if equipped.
  • Add oil to the hydraulic bar (pink).
  • Add oil to the bow thruster (yellow), always having a spare pin on board.
  • Check if any ores * have no guests on the axis or the propeller, if you have a trap door it will be even easier.

Annual maintenance

  1. Cleaning or changing the air filter.
  2. Regular emptying with the change of the oil filter (synthesis) every 250 hours or on average once a year. The level must be generally towards the maximum to ensure good lubrication even in the case of the cottage (but not above, which may raise the oil in the cylinders).
  3. Check the water pump-turbine, to ensure proper cooling of the motor. Change it every 250 hours preventively and always have a spare on board. A seawater filter must be cleaned every year…
  4. If your engine is equipped with indirect cooling, do a full drain of the coolant every 3 years and check on this occasion the thermostatic valve on.
  5. Check the motor anode every year but do not panic if it is worn, it is made for that
  6. If you have a recent engine with a timing belt, change it every 2000 hours (spare part to have on board).
  7. Regularly check the alternator belt (spare part to have on board). The changeover of the inverter depends on the brand, so refer to the manual or do it every 1500 hours.
  8. Do not forget to check the oil level of the injection pump (type Bosh, for example, the repair may cost $2500), otherwise, there is a risk of seizure of the cam; top up with engine oil or red oil as appropriate (see details in the forum section at the bottom of the page).

Apart from the timing belt that requires precision and a little equipment (depending on the engine), everything else can be done by the skipper, which is the best way to track the condition of the engine and is less dependent on mechanical trouble.

Maintenance of the shaft line

As a reminder, the stern post is the rear part of a ship, formerly called stern; also called stern mass, it is constituted by the rear extension of the keel.

On boats with inboard engines, the stern tube serves as a sheath for the propeller shaft which must necessarily pass through the immersed part of the hull.

The problem is that this device represents a risk of entry of water into the hold.

To ensure this, the marine mechanics have equipped this potential leakage point with a system that is both flexible enough to allow the propeller axis to rotate without being braked, and at the same time sufficiently tight so that it does not fail.


Do not put too much oil, and remember to replace the air filter immediately after filling and before starting the engine.

The start is often immediate and in any case, facilitated. Do not be surprised if the engine gives a little more smoke and noise than usual while it burns the oil added; it is normal and poses no risk to his health.

Clean hands full of grease

Use a dishwashing type degreaser or black soap; but the great trick is to sprinkle your hands with coffee grounds, which will act as a scouring powder.

It is natural and above all, terribly effective…

The auxiliary can ruin a week of vacation, or even become a pressing problem in the case of stopping the engine away from the boat when a strong wind blows away from the coast.

Check the quality of the Gasoline

It seems silly, and yet it can be the cause of all evils. If you take the gas as good and it is in poor condition, you can go crazy and fail to find the solution, no matter how much you disassemble and disassemble the entire engine.

When in doubt we must discard the old gasoline and go for a few liters of new gasoline.

When removing the cap of the tank, it is worth taking a look inside. If we observe some suspicious particles floating, do not doubt this gasoline is in poor condition.

We must empty it into discarded bottles of water and take it to the white point, or store it to burn it on the barbecue, but never throw it into the sea.

When gasoline is stored in its typical red plastic deposit for more than one or two years, it evaporates and the first vapors are those of its lighter volatile substances.

By inspecting the fuel filter located inside the outboard housing, we detect particles and deposits of gelatinous appearance, an unequivocal sign of the poor state of gasoline.

Some of these lumps can pass the filter and clog the fine ducts of the carburetor. We must change the filter and never keep the old gasoline; it will clog the new filter again.

The engine does not start? These are the most common causes

Now it is about solving the bulk of problems that are much more evident and almost always related to the carburetor. Suppose that the gasoline is in good condition and has not been mixed with seawater as we have seen in more than one case.

Therefore, the first thing we must ensure is that what we have in the tank is gasoline and not water or even worse seawater mixed with gasoline.

It is no joke, because in small engines with integrated tanks, if a clueless user or the previous client of a charter, has left the cap of the tank poorly closed, the water may end up entering and being denser than gasoline.

This will go to the bottom of the tank and will be absorbed by the gas pump stopping the engine without regard.

Something obvious that more than one forgets is to open the cap of the reservoir vent. If we do not, after a while of use, there is a vacuum in the tank and the engine will choke when gasoline cannot reach the carburetor.

1. Ignition, spark plug, and spark

We insist, that although an immense majority of the problems come from the carburetor and fuel supply, it is worthwhile to pay attention to the ignition. To do this, many modern small FB carries a Led light that indicates whether or not the spark comes up.

If you see that this indicator lights up, it is almost certain that the ignition is OK.

In any case, the final test is to disassemble and inspect the spark plug or put the spark plug pipe in another spark plug.

We will have to make the spark plug touch the metal crankcase to close the electrical circuit and give a couple of pull starts to see if sparks fly into the spark plug electrode.

The problem is almost certain the fuel supply. Inside the engine, in some models, we will find a sticker that reminds us of the type of spark plug that our engine uses and the separation that the electrode must-have.

It does not hurt to change the spark plug, especially if it looks bad or even more so if it has never changed.

2. Feed gasoline to the carburetor

Anyway, and to follow a certain order, it is a good idea to take the tube through which the gasoline reaches the carburetor and give a couple of pulls to start.

In case the flies and if your FB is of external deposit, tighten the rubber knob to assure that the circuit is well purged and loaded with gasoline.

When pulling the starter with the tube out of the carburetor, you should notice some small bubbles of gasoline pushed out by the tiny gasoline pump of the engine.

Possibly so be it and we’ll be sure that gasoline comes well until the carburetor, indicating what has been said … and the problem is in the carburetor.

If gasoline does not reach the carburetor, we should look at the circuit that feeds it and remove the gasoline diaphragm pump from the engine.

3. Battery is empty

This defect is easy to recognize for laymen: If the starter is somewhat worn out or creates no revolutions, then is very likely the battery is discharged or defective by a cell deadlock.

Another indication is when after turning the ignition key only a click is heard. Then, the magnet of the magnetic switch (see “2nd starter”) disengages the shaft of the starter pinion — but has not had enough energy to subsequently move the motor of the starter.

Normal car batteries keep (depending on usage) about 4-6 years. If the battery is discharged, the car can be bridged, or you replace the battery immediately with a new part.

If the cell is closed, bridging should be avoided as this can cause damage. If the battery is OK, the battery poles should be checked. These can be corroded after a long service life and thus hinder the flow of current.

It can also be checked whether the voltage remains on during the starting. The voltmeter is clamped between the positive pole and the negative pole, while a helper operates the starter.

If the voltage now drops to 8V or less, the guilty party is found: although the power is sufficient to produce a spark, the power of the starter is not sufficient to start the engine due to the low battery.

Practical tip:  

Anyone who switches on the interior light when starting can also recognize without measuring the device whether the voltage is maintained. If the light is almost completely dark, the battery has too little energy. A slight flicker is normal.

If the starter does not turn at all, not only a faulty magnetic switch but also a faulty ignition lock, a defective earth strap, as well as corroded battery poles can be responsible for the fact that no current flows.

4. Starter is defective

If the battery is OK, the first suspicion falls on the starter. If this does not start after turning the key, this can have several causes. Frequently, for example, defective contact bridges occur in the magnetic switch.

An indication of this is that the starter again makes only a clicking sound and does not turn.

The pinion thus engages, but the circuit at the contact is then not closed and thus the electric motor of the starter is not activated.

If the starter is turning “dead”, or miserable grinding noise is heard, this speaks for an expired pinion or a worn starter ring gear. Due to the defective gears, there is no stable connection between the starter and crankshaft – virtually “tooth failure”.

Here, it can help to push the boat forward in a high gear a little, so that the position of the starter ring gear changes slightly. With luck, the wheels now mesh again.

If nothing happens when turning the ignition key, it may also be due to a blocked magnetic switch. This can be a careful hammer blow on the housing to eliminate a “hanging” of the magnetic switch.

With luck, the starter pinion then retracts and the engine can be started. In the workshop, it is now possible to diagnose whether the starter must be changed or the starter ring gear replaced.   

5. Ignition switch defective

If the engine does not start, this may also be due to a faulty ignition lock. The following three symptoms can occur:

  1. Nothing happens at the turn of the key. Defective contacts in the lock do not activate the ignition. There are no warning lights; the boat behaves as if the battery is discharged.
  2. The ignition can be switched on by the ignition lock, but there is no activation of the starter at the start position of the key. The contact to the “terminal 50” is defective, which transmits the “start signal” to the starter. Therefore, no engagement of the magnetic switch can be heard.
  3. The starter is turning but the engine is only reacting for a short time – exactly at the moment when the starter is no longer actuated. This is because, in this type of fault, the ignition coil is not energized during cranking and thus does not generate a spark.

Attention: work on the ignition lock requires some basic knowledge in the handling of vehicle electrics and should, therefore, be carried out by a workshop of trust.

But what is to be done when the starter turns but the engine does not start? To do this, consider the two basic factors that the gasoline engine needs for a smooth ride: spark and mixture.

  1. No fuel

If the engine does not get enough fuel, it cannot start. An indication of the interrupting fuel flow may be that during start-up always short ignitions occur when there are still some gasoline remains to find their way into one of the cylinders.

There are many causes of fuel shortage:

The simplest would be a broken hose/line, which would appear on puddles under the boat, or an intense smell of gasoline.

In addition, also clogged gasoline filters or added carburetors come into question. Not infrequently, even a broken fuel gauge has led to a blatant lack of fuel in the tank.

Often it also occurs in motorcycles (especially two-stroke), as well as automobiles where the tank ventilation has been added.

For motorcycles, for example, this consists of a small hole in the tank cover, through which air can flow into the tank. This hole can be added by dirt.

Due to the resulting vacuum, the engine will run well only with a full tank. After a few kilometers, the back pressure of the tank is then no longer sufficient to fill the float chambers of the carburetor or to supply the fuel pump with gasoline.

Often it is the fuel pump that has given up its spirit. Practical tip: You can easily check this: If the ignition is switched on, the pump must make a noise (buzzing or tapping) in the first few seconds (if the fuel pressure is built up). Also pulsates with many vintage boats and then the fuel line easily.

Also, a defective relay may be at fault that the pump is not working. Finally, a defective fuse of the fuel pump can prevent the pumping of gasoline.

Both parts are usually located in the front of the fuse box and can easily be tested there.

Wrong mixture

Another reason that the engine does not start could be in the mixture itself. When cold starting the engines of vintage boats often require the use of the choke.

The mixture is deprived of air, which provides for a “richer (fuel-rich) mixture” and thus better ignitability.

If the choke cable is torn, or the operation has been forgotten, it can happen, especially in cold weather when the engine, although all other components are in order, does not start.

Of course, there are also more profound causes, such as an adjusted carburetor. If the air and fuel ratios are not set correctly, it will result in a rough run or the engine will not start running.

In workshop manuals, however, one often learns how many revolutions idling and mixture screw must be adjusted so that the engine starts.

Afterward, however, a correct setting of the CO value with the exhaust gas tester is still afterward.

Also, the automatic start of the carburetor may be defective. These are operated on many old-timers by the passage of the gas pedal once or twice before the start.

No spark

An error that often causes engines not to start is the lack of spark. An indication of a faulty ignition is that the engine does not jerk at all during startup, so it does not run short for a few strokes.

If nothing happens during the starter rotation, the ignition may be defective.

Check ignition

The best way to trace the path of the spark is to hold the longest spark plug with the spark plug out to the ground. Now, when a helper operates and starts the ignition, a spark should jump between the electrodes of the spark plug.

Attention, for safety reasons, always wear gloves and only touch the cable on isolated parts – it is best to rely on qualified personnel, especially if you have never done so.

Also, not all ignition systems can handle this attempt. The test with a stroboscopic lamp is therefore safer.

If there is no spark, there is a problem with the splitter, the distributor finger, the breaker contact, the ignition coil, or the ignition cable itself.

Most of these components are hard to test for laymen. However, the distributor cap can be removed after loosening the two springs. If water comes to you, the culprit is already found.

Adjusted ignition

If you have previously worked on the distributor or the ignition cables, it may happen that the ignition has been adjusted by mistake. If the distributor is loose-screwed on the shaft, you can adjust the ignition timing by turning the cap in the direction of early or late.

However, if the spark comes too early, the piston has not yet compressed the mixture – the engine does not start anymore. So if the engine gets a spark, you can make a rotation of the distributor for a later ignition.

However, one should go with a stroboscopic lamp and expertise (specialist workshop) to work – incorrectly set ignition threatens engine damage!

With the beetle motor, the distributor can be adjusted after loosening the screw

Another source of error is swapping the firing order. If you have mistaken the order of ignition to ignite the cylinder when the ignition cable, you get in the best case a non-circular engine running, in the worst case, the unit will not start – also threatening engine damage.

Lack of compression

Last but not least, missing compression can cause the engine to not start. For example, worn or “sticky” piston rings, as well as displaced valve clearance can ensure that the pistons can no longer build the necessary pressure to compress the mixture.

Last tip

The mechanics cannot be learned in books, but with tools in hand and grease on clothes.

The best way to progress is by spending time helping your fellow boaters or pontoon neighbors when performing maintenance on their engine.

First, they will appreciate your help, but most of all, you will learn a lot.

For those who would like to play more personally, marine diesel mechanics courses are regularly organized everywhere.


These were the most common causes of a boat’s warm or cold engine not starting. Of course, there are many more reasons why a boat, suddenly, will not respond despite being maintained the day, week, or month before.

With these tips, you should be able to fix every fault in the engine. However, if you’re not able to detect and fix the issue, consult a technician.

Recent Posts

%d bloggers like this: