Raven Yacht Owners Association

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Engine informationtitle

Engine Information and tips.

In this section



  •  Fuel leaks
  •  Black smoke
  • Starting a diesel
  • How hard should I run my motor
  • Steam from exhaust



Following tips etc relate to any diesel motor. 

The following is an excellent site for marine diesel information. It is by Volvo but relevant to any marine diesel.




        Detecting fuel leaks. Diesel fuel leaks are often hard to trace due to the clear colour of the diesel. A sure way to find a leak is to dry the engine with a cloths and shake talcum powder over the engine in the areas where a leak is suspected. Start the engine and any leak will become apparent. 

 Leaks often appear after a part has been dismantled and reassembled. It may be a o-ring not in place or damaged or because you have reused a copper washer associated with the assembly. The copper washers are generally one use only as they go hard and will not deform enough on reuse to provide a seal. If you do not have replacements you can heat the copper washers with a gas torch or similar and this will soften the copper washer for reuse.

Difficult to solve leaks can often be taken care of by using a Loctite product designed for sealing threaded fittings. This product applied as a gel foams in the absence of air and will fill any space in the thread or washer. See details on loctite site


Another thing that may cause leaks is a stripped thread often on aluminium products like fuel pumps. Instead of replacing the component you can have a new thread inserted eg helicoil, which will be superior to the original thread at a fraction of the cost of replacing the whole unit.


 Black Smoke from exhaust .

There are several things that may cause black smoke.

Lack of Air. If your engine has always given off black smoke especially under way the likely cause is that the engine is not getting enough air. If there is a black mark around engine covers etc this is a sure sign the motor is scavenging air through these joins.

Diesel engines need a lot of air to operate efficiently but often installations, trying to reduce engine noise, have not provided enough air intake. Following data from Yanmar.



Diesel Engines need Air to work properly:
Combustion Air (by weight) approximately 15kg of air (33 Lbs) to 1 kg (2.2 Lbs) of fuel 
and for Cooling.

Ventilation Requirements for Yanmar Diesel Engines:

1GM10 19.5cm2 3.02in2 50mm - 2" 
2GM20 39cm2 6"2 75mm - 3"
3GM30 48.2cm2
3HM35 74cm2 
3JH2E 84.5cm2 
3JH2-TE 120cm2
multiply cm2 by 0.155 to get inches2
100mm inside diameter tube duct area is 78.54 cm2 
50mm inside diameter tube duct area is 19.7 cm2
4 inch inside diameter tube duct area is 12.57 inches2 
2 inch inside diameter tube duct area is 3.15 inches2

A restricted exhaust elbow is another common reason for black smoke especially if it has developed gradually. The exhaust elbow collects carbon which bakes on slowly restricting the exhaust outlet. This creates back pressure which then indicates the motor has load and needs more fuel, which it does not, thus the black smoke, incompletely combusted fuel.

To check if this is the case the exhaust elbow needs to be removed and checked. The carbon is baked on so hard you have to chisel it out to remove. It is often better to replace elbow as the inside surfaces become pitted over time making it more likely to carbon up in future. It has been suggested that the exhaust elbow be treated as a service item and checked or replaced every five years or so depending on use of the motor.

The use of a stainless elbow has been suggested as stainless should not carbon up. Availability of these is not known. If you intend to remove elbow you will need a replacement gasket for the elbow-head join.

Another reason for black smoke is restrictions in the exhaust, other than above, or an over length exhaust. The exhaust should take as short a route to the rear as possible once provision has been made to stop backflow ie a loop/gooseneck well above waterline.

 Any bends should be kept as gradual as possible as each 90 degree bend in an exhaust is calculated to provide as much back pressure as two metres of exhaust pipe.

The exhaust  pipe should be of the same diameter as the exhaust elbow all the way to the rear.

Fouled Propeller. If your propeller has growth on it you will find that as you increase your revs black smoke will appear. This is more noticeable on a three bladed prop than a standard two bladed probably because of the greater surface area. Growth on the propeller causes the water around the prop to  milkshake up providing little forward thrust and load to the motor and as a result the engine is getting more fuel than it needs.

NB The Raven 31 transom is on a slope and often the stop cock follows this slope down before curving upwards  where the exhaust is joined. This should not be a problem even though water will sit in this area when the engine is not running. It often causes a bit of back pressure that will result in a bit of black smoke on starting ( especially if you have to crank the motor several times to get it started). This is not a concern.

Starting a diesel

A diesel with everything in good condition should start immediately on first revolution.

If it does not there can be several reasons, some easily fixed, others not so easy.

Battery. An adequate battery with sufficient cranking power, fully charged, is needed to give the quick spin needed to get the diesel started.

If your battery is fully charged and you are not getting good results it may be because of a voltage drop from the battery to the starter. This could be the result of inadequate sized wires or a voltage drop through the ignition switch. To overcome this adequate wires need to be installed and a relay put in the positive line. In putting in a relay you have a heavy wire going directly from the battery to the starter motor with a lighter wire coming from the starter bottom to close the relay when you press the button thus maximum power to the starter motor.

No fuel is an obvious problem. To check this, if there is fuel in the tank, loosen the bleed screw in the system. This is  often on top of the secondary filter on a Yanmar. Pump the lift lever on the fuel pump until a clear stream of fuel with no bubbles, should ooze out around the screw. If you continually get bubbles then the system is sucking air because of no fuel in the tank or a leak  in the line. Full details here on Yanmar motors from Yanmar help http://www.yanmarhelp.com/s_bleed.htm

If you have to crank your motor for sometime before it will start and you have checked out the above it may be because you do not have enough compression. This happens when the engine has many hours or has been damaged in some way.

A diesel requires 300psi of compression to ignite the diesel. If because of wear or damage it is less than this it will not start. The reason a tired motor will start after some cranking is that oil that has drained away while the engine is not going is pumped up providing a bit of extra compression. As the engine warms up components expand and improve compression. As a result of this a worn engine will start easily when warm but not so good when it is cold.

The motors you will generally find in the Ravens will if in good condition return about 400 psi. To check compression the injectors need to be removed and a compression tester  used. If compression is low it is then wise to check out whether it is likely to be the rings on the cylinders etc that are worn or whether it is the valves or perhaps head gasket. This can be done by squirting a small amount of oil into each cylinder after an initial reading has taken place and retesting. If an increase in the compression is obtained it indicates that the rings etc are the cause of the problem or if the compression does not increase that it is likely to be the valves  or head gasket etc. If it is the second it then only requires the removal of the head for reconditioning  or gasket replacement to improve the performance of the motor.

Low battery starting.

If  your battery is low on power some motors ie Yanmar have a lever on top of the tappet cover called a compression lifter. When this lever is lifted it releases the compression on that cylinder allowing the engine to spin quicker using less battery power. Once the engine shows signs of starting on one cylinder drop the lever and the engine should run normally. Saved many a boatie.

Most boats have two batteries, one to start and one to run the lights. These can have switching that allows you to use both batteries together if needed . However if one battery is significantly flatter than the other it may not work and jumper leads between the batteries is a better option.

Use of ether or other starting fluids can help in poor starting conditions as they have a lower compression ignition and will help get things started.

A warning about using these products is required as serious damage can be done  to the motor with incorrect use. A sort burst into the air intake is all that is required while the engine is being turned over. Do not squirt a continuous stream while the engine is turning over as this can cause a cylinder to fire in the incorrect order and bend the conrod or worse. I have first hand experience, not on my boat luckily !!!!

 How hard should I run my motor

 Once you have got your motor started a question often asked is how hard should I run it.

Everybody seems to have a different opinion . Here is what Yanmar have to say. Click on link for info.


Steam from exhaust.

As motors get older steam may be included in the exhaust. This indicates water circulation is being inhibited. The reason for this can include the following.

 : A salt water cooled engine operates at about 55degC / 130degF. This means it is quite easy to keep your hand on the cylinder block while the engine is running. If the temp goes over this the salt will precipitate out of the water and restrict the water galleries at an unacceptably fast rate. Because of this the alarm on a Yanmar salt water cooled motor  operates at 62degC / 144degF. The steam from your exhaust indicates that the water flow through the engine may be too low.

Check the following:
i) That there are no restrictions in the intake from the sea cock to the pump. You must dismantle everything if you haven't already and look inside or poke something thru that will remove jellyfish, small leaves, barnacles, etc.
ii) The hole in the thru-hull fitting sometimes gets smaller and smaller with each successive coat of antifouling. Go for a swim and check the hole is the right size. Don't rely on blowing through the system as it has to be very blocked up to provide any resistance to your huff.
iii) Where the water supply enters the cylinder block it splits and goes up to the thermostat bypass. When the thermostat is closed there is no significant flow through the block and head. When the thermostat opens it allows water to flow through the block, head and exhaust manifold to join the exhaust gas at the mixing elbow, and at the same time cuts off the bypass water flow. If the steam is intermittent the block, head or exhaust manifold galleries are restricted as the steam appears when the thermostat opens wide. I have not had any experience with Salt Away so I don't know if it works well or not. The white stuff you can see when you replace the anodes is a combination of extinct anodes and salt.
iv) On some model engines the thermostat cover can be installed in reverse. Check to see if it is the right way round, the word 'in' is usually embossed on the end nearest the front of the engine.
v) Check the raw water pump. You may find the wear is unacceptable and an overhaul is necessary. Check the cam, the cover plate and the inside face where the impeller runs and re-surface or replace if there are any grooves. Replace the impeller.
vi The exhaust manifold should be removed, dismantled and the water galleries cleaned. You have already cleaned the gas side and replaced the mixing elbow. It is possible that the manifold may need replacing at this age.
vii) The worst scenario is a cracked cylinder head leaking water straight into the cylinder while running. If you do things in the order laid out above they go from the more probable and the least expensive to the least probable and most expensive.

Several  Raven owners with saildrives have bypassed the intake in the saildrive leg by putting a new skin fitting in the hull close to the water pump. Often the problem has been corrosion in the stop cock on the saildrive which is often difficult to access.  By putting the skin fitting in front of the motor the stop cock is now easily accessible including any strainer you fit. Note . My experience with a Yanmar 2GM20 and associated sail drives with a water restriction has been two brass elbows. On my boat the first elbow was on the outlet of the stopcock on the sail drive where the pipe goes to the water pump. This was crusted up. Second brass elbow is on the front of the motor near the thermostat . This area has several small pipes and should be the first area checked if water restriction is suspected. Our mechanic recommends that this area be cleaned on each service.

Info from experience (contributed Keith Murray )

I have had cooling challenges but they have been in order:

Old engine
Faulty impeller - the copper flange was no longer stuck to the rubber impeller.
Broken impeller vanes - should have replaced it annually.
Perished hose on input side of the pump.  Once the engine started the hose would collapse from negative pressure and block the water flow.  Should have replaced it at year ten.
Blocked exhaust manifold after 15 years.  Where the water entered the manifold it was choked with salt.
New engine
Mussels growing inside the covers of the sail drive.  I could see them through the holes and used a stick to break them up.  When I put the boat back in the water some bits of shell were still in the cavity and blocked the water.  Solved by disconnecting the hose at the pump and using a garden hose to back flush.






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