engine care

a photo of a yanmar 2gm, with the front pieces removed

When acquiring Pino in 2016, we tackled problems as they came—not the wisest approach. Most engine problems are preventable, provided that all is checked and changed per the recommendations of the engine's manual.

Taking a diesel maintenance course can earn the novice enough confidence to take on the laborious, but necessary task of keeping a diesel engine healthy. We highly recommend it.

We combined our learnings into five categories:

Disclaimer: we are not diesel engine experts, although much of the notes below were advised by professionals as part of a course. We are not above making mistakes. If you find any, let us know.

Table of contents

Service inspection checklist

A list of common things to check and service on a diesel engine. Keep a logbook with service and inspection details, with notes on what was done, and when. Keeping a history of the engine is useful to determine future problems (it is also useful for the future owners of the boat, if it is ever sold).

Service items

See our resources for a list of helpful manuals on maintenance. Always carry the physical manual for your engine.


Change. Change the items below at scheduled intervals, per your engine's manual. Roughly 100 hours, or once per year, whichever comes first. After summer is best, it is better for an engine to sit in clean oil and fuel.

Checks. Do checks in the spring before the start of the cruising season (for those with cold winters).



Before running the engine do these four checks:

When starting engine, always watch at the stern to see if water is coming out of the exhaust.

Spares list

The amount of spares depends on the duration of the trip. A long-distance cruiser will evidently require more spares.

Engine component notes

a hand holding an oil filter for diesel engines


The only purpose of motor oil is to lubricate the engine. After the engine had seen some use, the oil takes on a black color, this is a byproduct of combustion. Modern types of oil prevent sediment formation in the oil pan, so there is no need to clean it.

Changing the oil filter. When changing the oil, always change the filter at the same time. To better siphon the old oil out run the engine for 15 minutes, heating the oil thins it out (it is near impossible to extract when cold). Jabsco Little Pal Marine Oil Change Pumps are compact, easy to store, and are useful to transfer the oil out of the engine and into a container for disposal (car shops and boatyards will take your old oil and filters). Removing an oil filter can be messy. To avoid making a mess, place a container and paper towels under the oil filter, grab a punch and puncture the oil filter so that it will drain easily into the container below. Making two holes is necessary, one to for air(oil won't come out without it) and the other for the oil to exit. Wait until it stops dripping and then remove the filter with a strap wrench. When adding a new filter, coat the o-ring with oil, and tighten it by hand. Check the engine after replacing the filter to see if there is a leak. Over-tightening the filter is not necessary, and can make it very difficult to remove.

Oil that is white (think mayonnaise) means that water is getting past a seal inside the engine, it is very noticeable and very bad for an engine.

Viscosities. There are many kinds of oil, each with their own viscosity and API (American Petroleum Institute) rating, usually displayed on a circle on the bottle. The more viscous an oil, the slower it will flow. Bottles of oil feature a SAE viscosity number, ranging from 20-60.

The first number. A 'W' preceded by a number on a viscosity rating means that it has been tested for colder weather (w=winter). The lower the W number, the thinner the oil, and the better the oil will flow on cold starts.

The second number. The second number means that the oil will maintain its viscosity and provide better lubrication at higher temperatures, or when running under heavy loads. Here in the Pacific Northwest 15W-40, a class of multi-grade oils, is the norm.

There’s a long list of API ratings and the time period for which they were created, for simplicity's sake here are the ones currently in use: CJ-4 for four stroke high speed diesels manufactured after 2010, CI-4 for vehicles manufactured between 2002 and 2010 and, CH-4 for vehicles manufactured between 1998 and 2002. Diesel engines feature two letters starting with a C, followed with a '-4', a lettering system that differs from gasoline engines. Diesel engine formulated oil will have additives not required in gasoline engines. Older engines don't need high performance oil (CF is the oldest type, but is obsolete).

If a bottle of oil bears the text 'energy conserving' it means that its viscosity allows for reduced fuel consumption (less fuel burnt to turn components inside engine), it also reduces friction.

Synthetic oil. Using synthetic oils is fine, because it is less viscous it is fantastic in cold climates. This kind also allows for longer service intervals.

Mixing different oil viscosities. As a general rule, don't mix oils of different types. In an emergency, mixing oils is fine, it is better than the engine running without proper lubrication. Some oils are less harmful if mixed together, for instance 10W30 and 15W40 oils are in the same range, they have similar viscosity ratings. They're categorized under the multi-viscosity variety, which means they offer good flow at both low and high temperatures. Mixing 10W30 and 15W40 won't change the viscosity of the oil too much, it won't damage the engine.


There are many belt types (v-belts, flat belts). Belts stretch overtime, and must be checked. An engine manual will explain how to tension a new belt. An alternator is a load on a belt and should not be too tight, otherwise it becomes a strain on both the alternator and the water pump.

An engine that is overheating can damage a belt. If the belt starts to create dust on your engine it is because it is too tight, too thin, or because the alternator is too big (too demanding for the engine size).

Salt water pump

The pump sucks sea water from the engine intake thru-hull and pushes it through the cooling system via a small rubber impeller. When servicing the pump as part of an annual check, take out the impeller to inspect it for wear. If the engine runs dry for too long (no water, due to closed thru-hull or blockage), it can damage the impeller. Removing the impeller with an impeller puller is ideal, it prevents damage to the housing. With a small impeller, it is possible to wrench it out using other means (using two screwdrivers), but it is difficult to do for larger impellers which sit deep into the pump housing.

When checking an impeller, check that the nubs are nice and round, and that all the arms are straight and intact. When inside the housing, the arms follow a curve determined by the shape of the housing, but should spring back straight when the impeller is pulled. Straight impeller arms will meet the inside walls of the housing perfectly, creating a vacuum that sucks and pushes the water through. If the arms are broken there will be no vacuum and no way to cool the engine. If an engine is allowed to sit for too long, the arms of an impeller can set in the wrong position, if that happens the impeller should be replaced.

Check the impeller for cracks between the arms, a severely damaged impeller will have arms missing. If it is missing arms, it will be necessary to check the engine for the lost bits (they can clog the system). The arms usually find their way to the heat exchanger. The impeller doesn't need to go back in any specific way, adding dish soap to help slide it back in helps. Dish soap is also useful if the impeller is hard to remove. If replacing the impeller, replace the gasket too (spare impellers usually come with it). If there is no spare gasket, it is possible to make out of thin paper, or to use liquid gasket. The pump will have drain holes in case the seal fails.

Many boat thru-hulls for engine intakes come with a grill, or a scoop. This is not a good idea. It is common for growth to form on the grill and scoop, which can in turn starve the engine. In truth, catching some seaweed or a jellyfish would also starve the engine, but the difference is that without a scoop/grill it is possible to fix the problem from inside the boat by poking a stick through the opening of the thru-hull rather than from the outside(requires you to dive under).

An engine that isn't spitting out a lot of water at the stern means that there is a blockage somewhere, either from debris, or from the accumulation of salt (especially true from sea water-cooled engines like our old 2GM). Check the engine's sea water lines to clear the salt, too little cooling can overheat an engine. This happened to us between San Francisco and San Luis Obispo. We could still run the engine, but at very low speed. Upon inspection, we found the water lines to be completely clogged.


Coolant in a diesel engine keeps it cool, keeping seawater from passing through the engine itself (not as corrosive for an engine). It is important to test the coolant once in a while to check the level of glycol to prevent freezing and to check the PH of the coolant. As it ages, coolant turns too acidic and can corrode the unit.

It is possible to buy pre-mixed coolant (more volume) or a concentrate (less volume, but you need to add 50% water). There is long life coolant and regular coolant, never mix the two. They come in a variety of colors, differing from diesel or oil so that it is easy to identify a leak.

Heat exchanger

A heat exchanger is a system used to transfer heat between two or more fluids, between sea water and coolant for a diesel engine. The coolant's job is to cool the engine, while the sea water cools the coolant, keeping corrosive sea water out of the main part of the engine.

The heat exchanger water pump is metal and integral to the unit, it cannot be serviced. If for whatever reason it fails, it must be replaced entirely. The coolant water pump has a drain hole, if the seal of the pump breaks it may leak through the drain. Lifting paint or discoloration near the joint is indicative of such a leak. There may be accumulations of salt at the mouth (or forgotten impeller bits) of the unit, which ought to be cleared. If flow is restricted, the motor will run hot. It is a good idea to periodically change the seal, it keeps the coolant and salt water separate. If the coil inside of the heat exchanger is sludgy, it is because the coolant has stayed in too long.


A muffler quiets the exhaust, and acts as a water lock for an engine. It is at its fullest when the engine is not running. Mufflers have drains, they can corrode and must be checked periodically. A muffler can be made of plastic, or metal. If made from metal, check for rust spots. Rust can be indicative of a leak.


Engines are full of hoses, varying in length, strength and diameter, made to withstand heat. Hard wire hoses are best, soft hoses can collapse and restrict flow. Tie hoses down to avoid chafe, apply chafe protection at key points. Check ends of hoses often, they are a common failure point.

When securing hoses to hose barbs use AWAB or T-bolt clamps, designs that have a smooth interior. Other types of clamps have sharp inner bits that can cut through a hose when under pressure. When applying a clamp over a hose to secure it to a hose barb take note where the barb ends to avoid compressing the hose itself, restricting flow and damaging the hose. The ABYC requires two clamps per hose, but if there is no room to put two clamps, put one. There is no point in putting two if only one can be overlaid over both the barb and hose.

The hose from the engine to the muffler ought to be as straight as possible, and at a slant (high from engine to low at muffler) to prevent the pooling of water. If the engine has been overheating, check this hose for damage. Hoses used with engines have many layers, and when there is excessive heat theses layers can begin to part and retain water. This type of deterioration isn't evident from the outside, but the parting is visible when the hose is removed.

Engine zincs

Zincs that are integral to the engine protect it from corrosion. The placement, and number of zincs varies on an engine. Check zinc condition often, replace before completely worn.

Heat exchangers uses pencil zincs. They have a standard length, but not all heat exchanger zinc housings can accommodate it. Before placing it, insert a pencil in the hole to see how deep it goes, and trim the zinc if necessary. Not cutting the zinc can result in breakage, and leaks. When screwing in new pencil zinc, add liquid seal at the head of the pencil zinc for a watertight fit.


60°C (140°F) is the max heat an engine room ought to have to withstand. Ventilation is more important for bigger engines. Small engines may have passive ventilation, with the air intake sucking up air from the engine room itself, and with the outtake coming out of an aft dorade. The forward motion of a boat is usually enough to suck out the heat, but otherwise a small fan fitted to the outtake duct is useful. Air ducts are sized to the engine power, make sure nothing is crushing the duct. Check periodically for delamination on the inside of the duct.


A great thing about diesel is that it's not as flammable as gasoline, see a demonstration of this in a video(YouTube).

For a fuel system to run well, the fuel needs to be clean before it reaches the injectors. It is the job of the primary, and secondary fuel filters to clean contaminants out of the fuel. Dirty fuel (water and dirt) at the injectors can damage them, because each part of an injector is tight-fitting with no play for anything other than fuel.

A fuel system starts from a tank, than is sucked up through the primary fuel filter, then on through the fuel feed pump (responsible for moving the fuel), the secondary filter and the injectors. On some engines, excess fuel may return to the fuel tank by way of another line (not all systems have this).

Fuel tank

To avoid condensation in the tank, keep the tank full in winter and check the deck-fill o-ring to make sure no water is getting through. Larger fuel tanks that can host over 30 gallons may have baffles. Baffles reduce the movement of the fuel within the tank, and aerate the fuel. Fuel tanks have a fuel pick up near the bottom of tank, it can get clogged if the tank has too much slime at the bottom (due to microbial growth). Most tanks aren't equipped with a drain, but they are useful to help remove water, and sediment at the beginning of the season. Diesel is lighter than water so if there is water in the fuel, it will settle to the bottom of the tank (the advantage of a tank drain is evident).

Water in a diesel tank can cause microbial growth. A brown and slimy fuel filter is a good indication of such growth.

Adding a fuel stabilizer with every fill-up is a good way to help keep the contents of the tank healthy (we use STA-BIL). A stabilizer keeps the fuel fresh, prevents sludge and sediment formation, cleans and lubricates your entire fuel system, protects against corrosion, reduces oxidation of diesel fuel caused by thermal breakdown, and helps remove water that bacteria, fungus and algae require for growth. Because modern diesel is not a great lubricant, using additives helps with performance.

Primary fuel filter

Primary fuel filters aren't integral to the engine, there are various models available on the market with their pros and cons. Most models have a clear bowl at the bottom, equipped with a drain and a spare port (if you want to add a water sensor). When the water collected in the fuel filter bowl covers the water sensor probes, the water-in-fuel sensor will sound an alert. Water conducts electricity, while diesel does not.

The fuel filter has to be accessible so it is easy to check for deposits in the bowl.

Fuel filters vary in flow rate, using a 10 micron filter at this stage is usually enough. A 30 micron filter as a primary leaves too much for the secondary to do. A filter that is too fine can clog up too easily.

Changing a fuel filter introduces air into the system. It is necessary to bleed the air out of the fuel lines for the engine to run. If there is air in the system, the engine will sputter and stop. When changing the primary, bleed the air by unscrewing the bleed screw near the secondary filter, and by pressing the lever on the fuel feed pump to push the fuel along. Once clear fuel exits the bleed screw, close it. Start the engine to see if it runs, if not it may be necessary to bleed the next bleed screw on the line before the injectors.

Fuel feed pump

A fuel feed pump is part of the low-pressure side of the fuel system. The pump sucks the fuel and helps it along through the rest of the system. The pump can be manual, or electrical (opens when engine is running). If the arm is up and that the diesel is sucked back in, this means that the pump has a problem and ought to be replaced.

Secondary fuel filter

Secondary fuel filters are next in line after the fuel feed pump, and are integral to the engine. Each engine has its own model (unlike primaries). If changing the secondary filter, it is necessary to bleed the screw between the secondary and the injectors (still on the low-pressure side). Yanmars have 1 screw to bleed, other engines may have more. Like for the primary filter, use the fuel feed pump to push the air out of the system.


Following the fuel through the system, injectors are next in line and mark the start of the high-pressure part of the system. They do not need to be bled after replacing the fuel filters, they usually self-bleed.

Bleeding air out of the injectors is only necessary if the engine runs out of fuel while running. To bleed the injectors, loosen all of the bolts (not just one, loosen slightly) and crank the engine (not full start). Cranking will push the diesel through and it will squirt it out of the injectors, when that happens close the bolts. This is a two-person job, but performing is alone is possible. If alone, tamp some paper towels around the injector bolts and go outside to crank, come back inside to check if the paper towels are wet, if so, tighten the injector bolts again.

Cold start

Like gas engines, some diesel engines have glow plugs, which helps when starting from cold. There are two kinds of glow plugs: fast heat, and slow heat. Slow heat is common in marine diesel engines, and need 5-10 seconds to start. To start an engine requires heat. Air compressed in the cylinders makes the engine hot. Diesels are typically harder to start in the cold.

If cranking excessively, shut the engine intake seacock to avoid flooding the engine, but remember to re-open it as soon as the engine starts to not starve the system.

Engine mounts

Engine mounts absorb the vibrations of the engine, they must be secure, able to withstand the thrust of a propeller. Typically, engine mounts consist of a piece of rubber between metal plates with a long bolt in the centre that secures the four 'feet' of the engine.

Look for rust, or signs that the rubber mount is deteriorating (uneven on either side). When aligning the engine to the coupling, it may be necessary to loosen or tighten the mounts to effectively 'tilt' the engine on one side, or the other, forward, or back.


As mentioned above, the alignment of the shaft coupling to the engine matters. When matching both plates, try metal to metal first (some couplings have a rubber bit in between) with a feeler gauge to measure the gap between them (it should be even all around, where the two halves meet).

A misaligned coupling wears down the cutlass bearing, the mounts and the shaft seal. If the coupling is loose, replace it. There are solid couplings and split couplings (with slot), a split coupling is easier to remove.

Stuffing box

There are many kinds of stuffing boxes. Traditionally, stuffing boxes consist of a piece of hose overlapping a bronze housing, with two threaded halves that compress lengths of tallowed hemp packing around the shaft. Traditional stuffing boxes always leak a little when the engine is running, but shouldn't leak when it isn't running, if it drips tighten the housing. Their advantage is that it is possible to change the hemp while in the water. When replacing the hemp packing, cut 3-4 separate lengths of material that matches the diameter of the shaft, with the 'cuts' made at an angle. When inserted the packing back in the housing, stagger the cuts so they don't align.

There are also dripless systems with rubber bellows. No-drip stuffing boxes come in a wide variety of designs (PSS shaft seal, tides marine etc), as their names suggest they do not drip water, even when the engine is running. All PSS shaft seals have a hose that exits over the waterline so that the system can pick up water to lubricate itself. Faster boats will need to have this bit plumbed onto the engine so that water is injected automatically (the speed makes it that no water can stay into the seal). Dripless seals are weak to chemicals, keep venting batteries away. They must be serviced every 5-7 years (replacing the rubber below).


A tired propeller will usually display a pinkish discoloration of the typically bright yellow bronze surface. The deterioration is the process of the metal changing back into it's oxide form. To measure the health of a prop, tap on one of the blades using a metal tool, a sound prop will sound like a bell (will ring long), while a bad prop will fall flat.

Avoid cleaning propellers with steel brushes and tools, the steel will embed itself in the propeller and can cause corrosion. Avoid using grease or anti-seize when installing the propeller on the shaft. Coating your prop, shaft and strut with PropSpeed (see image above) works well to keep growth off, it works well in high-growth areas (we used it in New Zealand and Japan) but it is very expensive. Grease the inside of your prop at every haul-out with a grease gun. Our propeller has a little screw that you can remove to insert a small nipple, which is used to pump the grease inside without having to dismantle the whole thing.

Check the prop alignment by doing the stick test. Put a stick between the edge of the strut and the flat of a blade, cut to fit, and turn the prop by hand. The spacing ought to be the same for every blade. A prop with a lot of pink means it is beginning to deteriorate.

Zinc anodes

Zinc anodes: to keep your shaft and prop safe, replace your zincs before they deteriorate. To ensure the anode stays put apply a coating of Tef-Gel or nail polish to the SS bolt that passes through the anode, and over the surface where the bolt passes through. Applying an insulating compound galvanically isolates the SS bolt(or machine screw) from the anodic metal.

If connected to shore power in a marina, use a hanging zinc to further protect your anodes. A hanging zinc is attached to a vessel’s engine block, and hung overboard into the water. Your hanging Zinc must be electrically connected to your shaft zinc to work. It's possible to buy them ready made, or to make them on the cheap. While in the boatyard look for a bin where people get rid of their old zincs, usually near oil/metal disposal sites. Bond an insulated wire (SS or copper) to the zinc, and run the wire through the boat and onto the engine block. Run another rope to keep the pressure off the wire when hanging the zinc overboard. Some people run the wire through a stanchion bolt, with another wire under deck connected to that same bolt that goes to the engine (ours goes through an aft dorade). When underway, don't forget to pull it up!

Cutlass bearing

A cutlass bearing lies at the bottom of the bronze strut (the part that holds the shaft outside the boat), it is what keeps the propeller shaft centred, and turning smoothly. It is a long bronze tube with a ribbed, rubbed inside.

To check if a cutlass bearing is still good, push the propeller shaft up (at the prop end), there should be no play. If it can be moved up and down, replace the cutlass bearing as soon as possible.

Misc notes

Extra notes that don't fit anywhere else.


Runaway diesel

Diesel engine runaway is a rare, but severe, condition affecting diesel engines, where the engine goes out of control, consuming its own lubrication oil reaching higher and higher RPM until it goes so fast that it destroys itself, due to mechanical failure or due to engine seizure(lack of lubrication). See an example of a runaway diesel engine at sea on Lady J(Beneteau Oceanis), the boat sank, but the crew is ok.

Diesels require three things to run: fuel, compression, and air. In the event of a runaway, starving the engine of oxygen is the most important thing.

You may want to consider installing a manual butterfly or swing gate air intake shutoff valve on the engine to be able to cut off the oxygen from the helm (there are also automatic systems on the market, at a higher cost).

Symptom Causes Solutions
Loud revving, turning engine off doesn't work Oil seal failure (turbo-charged engine) Block air intake with an object to starve engine to get it to stop, don't use your hand/body. Clean the oil out of the intake, remove oil/diesel mixture, replace seals, replace oil.
Overfilling oil crankcase. Block air intake with an object to starve engine to get it to stop, don't use your hand/body. Clean the oil out of the intake, remove oil/diesel mixture, replace oil quantity as specified by the engine manufacturer.
Damaged fuel pipes, or incorrectly assembled fuel linkages Block air intake with an object to starve engine to get it to stop, don't use your hand/body. Dissassemble problematic linkages, clean oil/diesel mixture, replace damaged parts.
Injection fuel pump failure Block air intake with an object to starve engine to get it to stop, don't use your hand/body. Clean the oil out of the intake, remove oil/diesel mixture, replace oil, have a professional service the faulty injection fuel pump. See an example
Hydrocarbons in the air Block air intake with an object to starve engine to get it to stop, don't use your hand/body. Find source of hydrocarbons.

Always check the rest of the engine for damages before re-starting, and make sure to have properly identified the culprit. Stand near and be prepared to turn the engine off again if the same issue occurs.


Exhaust leakage into boat

Symptom Causes Solutions
Water and or fumes in boat Corroded exhaust elbow replace exhaust elbow.
corroded muffler replace muffler
hose failure replace hose

Low engine power

Symptom Causes Solutions
cannot attain full revs, black smoke plugged exhaust elbow replace exhaust elbow.
collapsed exhaust hose. replace hose
clogged air filter replace/clean filter element (some can be cleaned)
insufficient air supply ensure ventilation is adequate
rope around prop remove rope

Exhaust water temperature is high

Symptom Causes Solutions
steam from exhaust water, possible elevated engine temperature exhaust elbow restricted at water injection point. replace or repair exhaust elbow.

Cooling system

Running hot

Symptom Causes Solutions
temp gauge reads high up to 93°C (200°F), or steam in exhaust esp. under higher loads. debris clogging intake strainer. clear debris.
damaged impeller. replace impeller.
restricted heat exchanger. clean.
restricted exhaust elbow. clean or remove elbow.
insufficient engine room ventilation. reinstate adequate ventilation.
loose fresh water pump belt. re-tension belt.
faulty thermostat. replace thermostat.


Symptom Causes Solutions
temperature gauge reads very high over 93°C (200°F), or alarm sounds. loss of coolant. locate/repair cause of loss.
broken fresh water pump belt. replace belt.
failed fresh water pump. replace pump.
leaking head gasket. replace gasket, or consult mechanic.

Running cool

Symptom Causes Solutions
temperature gauge reads low. faulty thermostat. replace thermostat (possible to remove it temporarily so alarm stops).
thermostat stuck open. replace thermostat.

Fuel system

Engine turns over on starter but will not start

Symptom Causes Solutions
no fuel at injectors. (white smoke when cranking means there is fuel). fuel tank empty. refill tank, bleed system.
stop control not fully in run position. re-position stop control.
clogged fuel filters. change filters, bleed system.
if lift pump has failed completely. change filters, bleed system.
fuel tank empty. refill tank, bleed system.
stop control not fully in run position. re-position stop control.
water in fuel. change filters, flush lines, clean tank (if possible), bleed system.
air in fuel, leaky fittings, filters or hoses. locate source of entry, seal and bleed system.
fuel at injectors. fuel return line blocked. clear blockage.
glow plugs not working (if any). check power to the plugs, replace if burnt out.
exhaust plugged. clear blockage.

Engine runs erratically

Symptom Causes Solutions
air in system. leaky fitting, filters or houses. tighten all fittings, check hoses and filter seals, bleed system.
fuel lift pump faulty. replace lift pump and bleed system.
no air in system. clogged fuel filter. change filter, bleed system.
faulty injectors. service/replace injectors.
clogged air filter. clean/replace filter.
restricted fuel pick up in tank. remove and clean pick up, bleed system
blocked fuel tank vent. clean/replace filter.
cracked injector pipe. replace pipe.

White/grey smoke

Symptom Causes Solutions
poor injector performance. service injectors (at a shop).
injection timing incorrect. correct adjustment timing.

Low power output

Symptom Causes Solutions
insufficient fuel delivery. *see erratic running causes. *see erratic running solutions.

Engine quits for no reason

Symptom Causes Solutions
stops suddenly. significant air in fuel supply, loose fittings, damaged hose. locate source of air repair, bleed system.
slowly dies away. air in fuel supply, fuel starvation. remove rope, *see erratic running.

Drive train

Abnormal vibrations

Symptom Causes Solutions
vibration possibly with rattling/thumping. loose engine mounts, poor engine alignment. tighten mounts, adjust alignment.
vibration with rattling noise loose shaft coupling bolts, coupling loose on shaft. tighten bolts, replace coupling/consult mechanic
excessive violent vibration, usually after impact with debris bent propeller or shaft consult mechanic
vibration with rumbling/rattling rear of boat. cutlass bearing worn or damaged. replace cutlass bearing
sudden onset vibration and excessive load, loss of rpm rope/weed/bag around prop and/or shaft remove obstruction

Loss of drive

Symptom Causes Solutions
shift lever on transmission operates normally, but output coupling does not turn. oil level low. top up transmission oil and test.
drive damper plate failed consult mechanic
clutch slipping. check cable travel, if adequate consult mechanic, if inadequate adjust linkage to allow full travel into gear.
shift lever on transmission operating normally and ouput coupling turns but not prop shaft. bolts on shaft coupling sheared or backed off. install coupling bolts and tighten securely. Check for vibration.
coupling loose on shaft, key sheared. consult mechanic.
shift lever on transmission operates normally and prop shaft turns. propeller key sheared. replace key, inspect for damage to shaft and prop (diver required).
propeller lost. replace propeller (diver required).
shift lever on transmission does not operate broken or disconnected shift cable. reconnect cable or replace as necessary.

Transmission noise

Symptom Causes Solutions
whine or rattle from transmission. low oil level. top up oil, check for leaks.

Contaminated oil

Symptom Causes Solutions
transmission oil turns white. water in oil, from leaking oil cooler. replace cooler, flush transmission.
transmission oil turns dark and smells burnt. clutch slippage check shift linkage adjustment, consult mechanic.