The Smoking Gun

[GordMay]

“The Smoking Gun “ ~ Interpreting Diesel Exhaust Smoke:

Diesels are simple in concept and much simpler than gasoline engines, since they have no ignition and associated timing or electrical issues. They rely on two key principles to operate; they use very high compression to heat the fuel air mixture to it's flash point to gain ignition, and use a highly compressed stream of atomized fuel injected directly into the combustion chamber. Additionally, a major difference between gasoline engines, is that diesels rely on a "governor" to attain and maintain engine speed. In a marine gasoline engine, you apply throttle to provide additional power. Doing so adds a specific amount of fuel. In a diesel however, when you apply "throttle" you are really advancing the governor control. Its job is to maintain the set RPM as dictated by throttle position. If the load on the engine changes, the governor will automatically call for more fuel (or less) to meet the load requirements. This difference between gasoline and diesel engines may seem subtle but as you see when troubleshooting it will play a key role.

The diesel fuel system consists of a low pressure fuel pump, which maintains a constant supply to the high pressure (injector) fuel pump. In a four cycle diesel engine, the high pressure pump is a piston like arrangement that pumps each rotation of the crankshaft. The injectors located at the cylinder head have a check valve that prevent fuel from being pumped into the cylinder during the compression cycle and also prevent exploded combustion gases from being forced into the fuel system. Fuel not used during "off cycles" is returned via a return line to the fuel tank.

The injector system operates under very high pressure (approximately 3000 PSI). Consequently, only rudimentary testing of these devices can be performed without special equipment.

Diesels need only two things to run:
1. Adequate fuel and air (at the right time and quantity)
2. Adequate Compression

Since you have no ignition, the only way to stop a diesel is to eliminate one of the above (typically by shutting off the fuel supply). The only way to start one if you have BOTH these thing!

Let the smoke tell you what's going on in your engine!

Presuming it will run, you can tell a lot about what is going on in the engine by looking at the exhaust. Many problems, either present or slowly coming on can, be diagnosed by the exhaust smoke.

All diesels will throw a little excess black smoke when accelerating. That is normal as it takes the system a little time to develop the RPM and power necessary to burn all the fuel being provided. Remember, the governor immediately provides whatever fuel is needed to get to a given RPM. If the engine can't get to that RPM, the governor just keeps throwing more fuel at the engine to try!. If the engine smokes much more than a very faint cloud during operation it means something is probably not right. Here is what to look for:

BLACK SMOKE:
Black smoke is generally be caused when the fuel does not burn completely, and the partially burned particles are expelled in the exhaust. When this occurs it means the engine cannot reach the RPM that is being called for by the governor ,in one or more of the cylindesr. There are two reasons for this:

1. The load exceed the power capability of the engine
2. A Load within the power capability of the engine cannot be handled because of something wrong in the basic engine system (IE compression or air/fuel mixture)

The first thing to check for is an air inlet restriction such as from a plugged air cleaner. Take off the air filter and make sure the intake port is clear. If the engine still smokes with the port clear and the filter off, the problem is elsewhere.

Injector malfunction is also a potential common cause for black smoke as is incorrect engine timing. For example in a two cylinder engine, if you have one bad injector, the system cannot develop the RPM to burn the fuel called for since the properly fueled injector is working against an essentially dead or less than efficient cylinder. A poor cylinder will put out black smoke if it is getting fuel, because compression problems prevent complete combustion. The good cylinder will put out smoke, because it is being supplied more fuel than it can effectively use. You may be advised to remove the injectors and have them checked at a competent shop.

To check compression, you will need a compression gauge that can measure pressures over 500 PSI. Additionally, since diesels have no spark plug holes through which you can test compression, you must accomplish this be removing the injectors and using those ports. You will need a special fitting to use the injector port from testing. If you have a compression problem, it could be caused by bad rings/cylinders, valves or valve guides (or unusually, a hole in a piston).

Typically, if you have a problem with valve guides, you will have a lot of "blow by".
Ie: The crank case will be pressurized, and you will see pulsing puffs of exhaust coming out of the engine crankcase breather.

You can determine if you have bad rings/cylinders only by inspection. However, if you pull the head and find the valves in good condition, you'll know they are bad. By the way, before you pull the head, check for valve clearance and make sure all of the valves operate.

WHITE SMOKE:
White smoke usually occurs when there is not enough temperature to burn the fuel. The unburned fuel particles are then exhausted, usually with a rich fuel smell. In cold weather, it is not uncommon to get white smoke until engine temperature builds up. Low engine cranking speed can also create an excessive amount of white smoke.

If the problem persists, after the engine is up to operating temperature, several other things should be checked. A faulty injector can cause white smoke. Timing is often a factor when white smoke is excessive. Low engine compression can cause the problem and the injection pump can also have problems that result in white smoke. Air in the fuel system can also result in white smoke.

Lastly, steam (caused by a head gasket or other water leak into the combustion system) can disguise itself as smoke. Steam will dissipate rapidly once it hits lower temperature ambient air, while smoke will persist in the air.

BLUE SMOKE:
Blue smoke is a sign of lubricating oil being burned by your engine. If you have blue smoke, mainly at start up (and it is very minor while running), this points to worn valve guides. When the engine sits for a bit (over night etc), oil left in the head after running can seep down into the combustion chamber. Upon start the bulk of it is burned quickly.

If you see blue smoke all the time when running, odds are you have a problem with rings or cylinders or both. Although, sometimes a little solvent in the cylinders (left overnight) may free rings stuck up with carbon, usually, you will have to pull the engine and rebuild it to get things back to normal.

HTH,
Gord May

[Alan Wheeler]

Well writen Gord.
If I may add (hehe again)
Two of the most common problems seen in a Marine Diesel would be, A Sticking Valve and a Glazed bore. Both faults can be hard to cure, but both are easy to prevent. It just means regular running of the engine, or properly putting to bed for the winter. Lets start with the Glazed Bore. The biggest mistake made with Deisels is the idle to warm them up. These engines just do not like it. So here is the best way to start.

Firstly, leave the lines tied to the dock or stay at anchor/mooring if you don't want to go anywhere. If you are travelling, then the following can be done underway.

Start the engine with throttle just above idle. Not tooo much, but just enough to not allow the engine to run too slow. Diesels will often start at a very low RPM when really cold even maybe only a few cyclinders firing. This start period is where the most wear accours to high load area's. The oil pump must build correct pressure to maintain the correct tolerances in bearings. This is just for maybe the first 10 to 15 seconds of start up.

As soon as Oil pressure has built, place the boat into gear. At a Dock, this can be forward, at anchor, this may be reverse. It doens't really matter. Allow the prop to turn about 30seconds to allow the gearbox to be properly lubricated and then raise your throttle to about 1/3rd of your RPM range. Allow it to run at this speed till the engine starts to warm. You will notice the engine will change its note a little as it warms. As soon as you see the temp gauge start to rise, increase throttle to 50%. Allow the engine to come to 50% temperature and then raise throttle to normal operating RPM. Allow engine to come to full temp. Then you can shut her down.

Deisels MUST have a load placed on them as soon as possible. Deisels MUST NOT be allowed to idle cold for long periods.
You may even note that doing this to a previousely blue smoking engine at start up, may even cure the problem.

To stop the Valve sticking problem, runt he engine regularaly. Minimum of once a month. Preferably once every week or two weeks at the most. If you can't for longer periods than a month, ie winter, then you need to winter proof the engine. This means oil change, anti-sieze spray like WD40 around and over the engine and in the intake. You can even squirt the stuff lightly down the intake as you shut the engine down. You can also remove the wet exhaust injector and allow the exhuast to flush what is in it. But this must be brief as you don't want to heat the exhaust. Then Stuff a rag back up the exhaust to prevent moisture working back up into the valve area.
Have to go to work now, but I will post later about a couple of other trouble shooting tips when an engine maybe starving for air.

[BC Mike]

A Yanmar 13 hp had this problem and belched white smoke, a lot of it back out the air box. I asked amny folks to diagnose the problem based on the smoke and noone got it right, including me, but when we were cranking the engine I could here the valve sticking. I took the valve cover off and with the rocker off and the piston out of the way tapped on the end of the valve until it opened and closed freely.
Michael

[Alan Wheeler]

Glad to hear it was a simple fix Mike.

OK as I said this morning, I would suggest some hints for detecting Air supply problems.
Actually, lack of Air to a Diesel engine, is one of the biggest causes of Black smoke. If you engine has started to Black smoke, check the Aircleaner as the first approach. A cleaner with a paper filter may have become damp or it just maybe clogged. Simply put, Diesels need large quantities on unrestricted air. Maybe I should add here, part of getting the air into the engine means you have to get the exhaust out. So a well designed Exhaust is just as important as any other part of the Air supply. I will come back to the exhaust. A good air supply to the engine room is the first start. Especially a fact for the high horsepower Launch guy's. The air supply does two things. Firstly it is required for the combustion, but it is also important for heat management in the engine room. Not enough Air circulation in and most importantly, Out of the room, will allow the room to sit at a very uncomfortable temperature. This isn't good for equipment down there, but one thing often overlloked, is hot air is not very dense. So this results in less Air entering the engine for combustion and results in lack of power and black smoke.
So whats a tell tale sign of lack of Air to the engine room? Well firstly you need proper vents. But I have actually seen boats with engine intake vents that have still been too small. It's quite a common aspect to see if someone has done a repower to a bigger engine. So depending on your design of engiine room and where the air comes from, take a look around cracks in floor panels. Especially if carpet is is over the floor. Over time, a little of that black smoke gets sucked back into the boat and if the engine room is actually a vacum, because it can't get enough air in the way it was supposed to, then the surrounding air gets sucked down into those litle voids. I have seen one boat, that this was such a problem, black lines ran across the carpet at every floor joint.
So to summerise, a Diesel needs plenty of cool and unresticted Air to perform efficiently. ESPECIALLY if you have a blower or turbo on the engine. Then the volumes of air that get moved is startling.
Oh and back to the exhuast. If you can't get the exhaust out, then you can't get more air in. So an unrestricted exhaust is most important. Actually, and exhaust back pressure of only 1PSI is enough to upset the apple cart. Remember that water is also injected in the the system if it is a wet exhaust. This takes energy to get the water blowing out the back. In a perfect world, the bigger the exhaust the better. BUT!!!! Boats aren't always perfect worlds and we are often restricted to size.

I hope that was of some interest or help to someone. In keep thinking there is something I have forgotten but????

[Alan Wheeler]

Oh yeah, now I remember. On one Launch many years ago, we fitted two very large Air blowers to the Engine room, to positvely charge the room with Air. The owner was lucky that he had the Alternators to be able to cope with the power demands. Probably not something that could be done to a small yacht engine compartment when you have a little engine working it's butt off to charge the batteries and the blower sucks as much juice out of the banks as the Alternator is trying to put in. However, on this bigger Launch, the problem was solved very easily. It was so long ago, I can't remember what the issue was for not being able to simply add a larger Air vent, but....

[Amphibian]

Gord and Alan,

Thanks ever so much for providing valuable info on subjects that I otherwise would have to read many textbooks to obtain!

Avgas is going out of style, and diesel engines are being developed for small aircraft. Many airports don't even offer avgas (100LL), only jet A-1. We could use mogas, but there's a risk of contamination that only a few are willing to take.

The one diesel at our airfield had some black sooty streaks on the fuselage, emanating from the tiny openings around the engine cowling. Owner believed this to be normal for a new diesel.

[Jentine]

The free flow of air into and out of a diesel engine is more important than most think. Some years ago, I assisted in the delivery of an Ericson 35 to the Chesapeake. The engine wouldn't get to full power and in no air failed to produce more than three knots. The owner sought a solution from more than 20 mechanics at various marinas from Virginia to Florida. After a failure of the engine to keep running, he enlisted the assistance of a mechanic in Florida who was stumped by the problem. They sent the fuel system (pump and nozzles) to a fuel shop for inspection and calibration, tested compression, checked the valves, checked the transmission, and every other test one could perform.
The mechanic, after several weeks of work, decided to remove the exhaust. The owner,thinking that the mechanic told him to hit the starter, did so and the engine fired and ran fine. The problem, a clogged exhaust, was found by accident. Sometimes it pays to have bad hearing.
Diesel engines require a free flow of air in and out. That is why trucks have such large air cleaners in comparison to gasoline engines.

[BC Mike]

At Yanmarhelp.com that is usually the first thing suggested to check.
Michael

[JGI417]

Has anyone ever heard of getting a bad fuel filter,
Two years ago after replacing the secondary fuel filter on a m25 Universal, I ran the engine an it quit like I ran out of fuel. After some trouble shooting I traced the problem to the filter I replaced. after replacing it again, no futher problems
No one I have talked to ever heard of this

[Alan Wheeler]

You would hope not, but from experiance, you never say never.
One question, you replaced the original filter why? was it just general maintanace or was it also blocked? Could you see anything in the faulty filter? I common fault has been when a bug has been in the tank. The filter gets blocked and gets replaced, only to have another mouthfull of the stuff go through the next filter.
Another fault can be if that replacement filter had been wet. The paper may have swelled and blocked up its minute holes. I had a filter do that once. It wouldn't allow anything through it at all. Although it swelled due to water in the line, not that it was damp when put in.
Otherwise, I can't think of anything else.

[Strygaldwir]

I have heard of many people having difficulties with filters that were not engineered for the higher pressures that fuel injection require. Diesels and older Porsche's have pressure regulated fuel delivery systems. For them to function the working pressures of the fuel can be very high. If you don't have properly rated filters, they can disintegrate.

Always go with the manufacturers recommendations on filters, unless you are VERY well versed in the construction and working requirements of your filter and engine.

Keith

[Alan Wheeler]

Hi Kieth, that is a little unusual that the supply side would be high pressure. Most usually it is low pressure feed to the Injector pump. Plus you would normally have, or I should rephrase that to, you should normally have a standard water/fuel/seperator/filter system on a boat. These are standard systems and range from a simple little dinkydie thing on the yanmars through to the sophisticated and expensive Racor filtration units in bigger engine rooms. CAV is another good unit. The big advantage of these filter systems, is ease of filter replacement. Infact, the big Racors can even have the element replaced while still operating.
When you are talking of Porche and other petrol based fuel injection systems, you then have a high pressure fuel pump. Nominaly around 30PSI, depending on manufacturer, some can be much higher. This is because there is no injector pump. The fuel pump pressurises a fuel rail that the injectors are fitted into. These are then opend via an electrical pulse. A Diesel injector is opened via a pressure pulse delivered from the injector pump.
The big rule of supply side to a diesel fuel pump, is a good flow volume. They must have a good unimpeded flow. There is a large quantity of fuel returned to the tank because the fuel is used for cooling of the pump.

[JGI417]

I replaced the filter for normal maintenance, and it was a universal filter. still in in the box and was not opened. I should of kept the old filter and cut it open to find the fault. Its possible that I could of have some water, but I replaced the primary filter and checked the bowl and it was clear, I keep the tank full over layup and also treat the fuel.
Thanks for comments

[sundown]

About a year ago, I (briefly) got water in the head of my Volvo 11 engine. I had a mechanic tear the engine down and solve the problem (I had put the exhaust gasket on backwards). When he put the engine back together he said that the rings etc were in fine shape and did not have to be replaced. He also suggested that the rings would have to be reseated.
For various reasons I have not been able to use the boat much since the 'rebuild' and the engine has mostly been run at an idle for maybe 20 hours total. I am being told by my fellow wharf rats that I may have already glazed the cylinder walls by not breaking the engine in under load.
I have moved the boat next to the float and am putting load on the engine by towing on the bull rail. The engine does smoke excessivly until it comes up to temperature and I notice the wet exhaust is leaving an oil slick. Is there anything else that I should/could be doing to break this engine in quickly? How many hours of running under load should I expect before there is an improvement in the smoke at cold start?

[Yacht Spirare]

Hi Allen,

Can you elaborate on why Sticking Valve occurs on old engine ?

It has just happened to me yesterday. Starting the engine...a "pop" "pop" sound alerted me to something wrong. Stopping and restarting engine...it very quickly resolve itself in about 5 seconds or running at idle. I suspect a sticking intake valve but I am not sure how to differentiate between sticking intake or exhaust valve ???

In my case, the engine is a Universal 5424 (1986 3 cylinder) with 4700hrs. It is being use hard as I am living aboard since 2009 and sailing around the world... but always under load. Valve adjustment is proper and injectors have been changed last year. Compression is good, it starts easy even cold, has no sign of smoke except a little momentary blue haze throttling up after any extended time either idling or just cruising at regular speed (usually 75% of full throttle). This is probably a sign of worn valve guide but on the other hand, this does not happen on cold engine starts.

Regards,