Black, oily residue when starting ....

[Scott T-Bird]

One thing that has bothered me ... even when the engine is warmed up, any time I start the engine (Yanmar 1GM - 1983 vintage) I have a brief period where the exhaust smoke is black and the initial squirt of water is filled with a black residue that floats on the water. Since our lake water is relatively clean, it bothers me. It only takes a few seconds before the exhaust is clear and the smoke disappears, but still ...

The colder the engine, the longer the period of black smoke and the more residue that ends up in the water. It isn't really an oily sheen except for when the engine is very cold like it is in the late fall.

Yesterday, with overnight temps in the 30's and daytime temp in the 50's, I wanted to go for a sail and it seemed like I may not be able to get the engine to even start. I had to turn it over several times (bursts of no more than 3 to 5 seconds) before she finally coughed to life. In this instance, an oily sheen was spreading from the exhaust while turning the engine over. There are no glow plugs on this engine ... is this going to be needed at these temps? Next weekend may be the last before the boat gets hauled.

 

[Stephen Trapani]

Hi,

I commonly had this problem with my Yanmar 2QM15, 1979 vintage. Apparently it was due to lack of use because when I began running the motor more and harder, the problem went away. I will still get black smoke at higher RPMs after long periods of disuse, but if I gradually increase the RPM over a period of about 2 or 3 hours, that goes away too. People advised me to run it hard, but I couldn't stand seeing the black smoke so I would take it out and gradually increase RPMs, backing off if I saw smoke, and I could gradually get it all the way up without smoke. This only works under load, not in neutral.

I also had the starting problem you do until I got a bigger starting battery. Apparently these motors start much better when you spin it faster. Also, full throttle with some pumping. With mine, once the engine is warm it starts extremely quickly.

Don't know much about your motor, but if it's anything lilke the 2QM15, it's well worth figuring out. When I change the zincs, those passageways look new, zero apparent corrosion. When we had the head off we were unable to see any scoring of any sort, also new looking. Pretty amazing for a 31 year old motor.

 

[Ross]

The black smoke is carbon soot from the fuel oil not burning clean because it is not yet hot enough. Look at large diesels that are being started at this time of year they can blow smoke for ten minutes or more. The system is feeding the engine more fuel than it can burn because the rpm isn't matching the throttle setting.

 

[Ted]

Black oily residue when starting

Another possible cause can be attributed to the way you shut down the engine. Yanmar recommends that you raise the rpm's pretty high just before you pull the fuel shut off cable. This prevents unburned fuel from sitting in the combustion chamber which will exit the exhaust the next time you start the engine.

 

[Scott T-Bird]

I've wondered about the mixing elbow. Last season I pulled it and could see a very hard, black film. I scrubbed with a wire brush and soap solution. After realizing that I was not removing anything, I gave up. The openings appeared to be normal but I wondered if it was worthwhile to simply install a new one. In the end, I just put it back on because I don't seem to have any problems with it under normal use.

I do know that the engine is not being worked hard enough. I spend time motoring around the lake to give it a work-out but the prop seems to be oversized and the max RPM is just 2,400 when under load. At 2,400 rpm the boat speed is 6.2 knots (measured by GPS with no current), which is about the theoretical boat speed (or maybe just a little under). I get just a hint of black smoke, which disappears when I back it down to 2,300 rpm. Of course all of this is assuming that the tach is accurate but I read 3,700 rpm when in neutral full throttle and according to the documents, I should get as high as 3,800 so I figure it should be good. In any case, I am changing the prop this winter to better match the boat and engine.

Possibly, with the prop matched correctly and working the engine at over 3,000 rpm on a regular basis this issue may get better, I hope. I wondered about the batteries ... with the colder weather I have taken to starting with the 2 batteries combined, but even so, it doesn't seem like it spins it very rapidly. When it is warm, the engine jumps to life.

BTW, do glow plugs help and how do you go about installing them (what are they exactly)?

 

[Stephen Trapani]

I wondered about the batteries ... with the colder weather I have taken to starting with the 2 batteries combined, but even so, it doesn't seem like it spins it very rapidly. When it is warm, the engine jumps to life.

Sounds like you need new batteries, or they are not fully charged. I got the biggest starting battery I could fit in the space. I also use both banks on cold starts. Ever since then, the motor starts after about ten cranks even in the coldest of Western Washington winters. Prior to that I was lucky to ever start it when cold before the battery died, even in summer. I used to have to spray stuff into the intake to start it (NOT recommended).

 

[RAD]

The issue your having might be from the engine not able to reach max rpm and soot build up because of the prop, I had an over pitched prop for a season and the transom got full of soot when I pushed the boat and I didn't have a tach so I had know idea anything was wrong so I'm thinking your looking at soot mixed with water coming out the exhaust

 

[Ted]

Black oily residue when starting

When the air temperature drops and your engine has a difficult time spinning fast enough to start, do the following. Flip your decompression lever, then engage the starter. When the engine is spinning fast, flip the decompression lever to the normal operating position. For a two cylinder engine, flip one lever at a time and you should be good to go. I don't believe that you can easily add glow plugs to an engine but you can warm your fuel line with a hair dryer to help raise the temperature of the incoming fuel. That will make it easier to start in cold weather.

 

[galynd]

The Yanmar 3gm manual says to give full throttle when starting cold. I do this but quickly pull the throttle back as it starts. Without doing so it'll turn over forever without starting. cranks first time everytime when fully throttled.

 

[Bill Roosa]

Diesel basics

Diesels are heat engines. The compression of the piston makes the heat that ignites the fuel. With cold air the compressed air temp is lower. With slow cranking the compressed air temp is lower. So cold winter air and a cold battery with reduced cranking capacity is a worst case scenario.
Anything (bad rings, leaking valves, air intake restriction, exhaust restriction) that keep a full charge of air from entering/leaviing or allowing it to escape as it is compressed will cause the engine to be harder to start.
Black smoke on cold start is not much to worry about if it is only momentary. The cold cylinder walls suck the heat out of the compressed air and you have to use a higher throttle setting to get any specific RPM. So you are pumping more fuel into the engine to get it to idle and the rest is just not combusting compleatly. Once the cylinders heat up the fuel gets fully burned, you back off the throttel due to increased RPM and the black smoke goes away.
You can check the rings, take the oil fill cap off while the engine is running and note the amount of blow by. You should do this before you have a problem so you know what is normal. If it fills up the cabin with smoke then you have a problem. Less that that may or may not indicate a problem. No blowby is clearly a good sign.
Black smoke under load is not much to worry about either. It does indicate that the prop, engine RPM and boat speed are not matched. Could be due to the prop pitch or a fouled bottom. Fouled bottoms are a seasonal problem and we normally get those questions in fall.

 

[Hermit Scott]

I do not believe you can add glow plugs to your engine. In the cylinder there are two valves and an injector pump. There is just no room for anything else. Even if there was, I am an idiot/maniac when it comes to doing things like that and I wouldn't ever consider it an option.

The fuel air mixture becomes more and more flammable the more it is compressed. A glow plug is an electrical heater that is hot but not hot enough to ignite the fuel air mixture coming into the cylinder at regular room pressure. When the piston compresses the fuel/air mixture it becomes flammable at the heat temperature of the glow plug. Then it explodes. That's all for a diesel.
A gas engine fuel mixture is always ready to explode, that is why compression values for gas engines are 1/2 as much (examples -diesel 20:1 gas 10:1). IF you tried to burn gas in a diesel before the piston could get half past the way up the cylinder the fuel mixture would explode before the piston got to the top.
As you increase the pressure of a gas, you increase the temperature. A cold cylinder may hinder the diesel/air mixture from reaching that temperature by sucking the heat out.
About internal combustion engines, the compression ratio determines the maximum efficiency. Diesels are 20:1, gas engines are 10:1) so by those numbers it should take twice as much gas to get the same power out of it. All this is simplified just to give you a jist of what's going on in your engine.
In my opinion your engine needs some tuning or some work done on it to run better.
Some possible causes off the top of my head are something leaking in the cylinder and not allowing the compression to reach the maximum that it needs to. IF your injector spray is not properly atomized it could be more difficult to make it explode by pressure alone. You can take that injector out of the cylinder and turn over the engine and watch what the spray pattern looks like. I must warn you though, on my yanmar I clamped the head to my 1000 lb. welding table and used a 4 foot long cheater pipe to twist it free. I had to use both feet like I was squating it. It wasn't even threaded in, there is a flange that puts pressure on it that I removed first. It would have never came free in the boat.

The 12 hp diesel is barely enough in my boat. It strains to push it when the chop is up. If I run it full throttle for 20 minutes or more under load, it starts pouring oil out of the exhaust.
And the engine bogs down and loses RPM's. I can only guess what is happening; the cylinder heats up too much and the piston rings can't seal the cylinder for some reason and oil starts leaking by. It is weird because it doesn't gradually do it. It's fine one second the next it's pouring oil. When I power it back it's fine again. I don't know what the deal is.

 

[Bill Roosa]

Diesel basics 102

Diesels do not have fuel air mixtures. The intake manifold has no throttle (butterfly valve) like a gas engine. It is just a tube and the engine sucks in a full (WOT in a gas engine) air charge EVERY time there is an intake stroke. The "throttle" is just to control the amount of fuel that the injectors squirt into the combustion chamber. They squirt the fuel at a precise moment at the top of the compression stroke similar to the timing of the spark on a gas engine.
There are two basic kinds of diesels, direct injection and indirect injection. The direct injection type has a cylinder head very similar to a gas engine with the fuel injector replacing the spark plug. They do not have glow plugs. The indirect type has a small (very small) side chamber in the cylinder head that houses the glow plug and fuel injector. During a cold start the glow plug is preheated to red heat (actually glows red) then the engine is cranked. The hot metal of the glow plug ignites the fuel charge when it is introduced. The power and heat released by the explosion heat the metal and increase the engine speed so the next compression stroke heat the incoming air more. Three or four cycles later the engine does not need the glow plug and runs off its own compression. Most of the time the glow plug is just along for the ride.
You can burn most any hydrocarbon fuel (gasoline included) provided they provide sufficient lubrication for the injector pump and injectors (gasoline does not but you can put some 2-cycle oil in it and be fine!!!!!, just have to get the concentration ratio right)
The compression ratio does determine the efficiency as Mr. Scott mentioned but the relationship is not 1:1. There are those pesky laws of physics rear their ugly head and limit diesels to only a few percent improvement over a gas engine. Google "Carnot heat engine".
If you experience the sudden onset of smoke and power loss it is surly not the rings or valves. Especially if it goes away with reduce power settings on the throttle. I would suspect an exhaust restriction (mixing elbow?? muffler full of water or having to lift too much water at full power water flow rates, or hose??) that will not let the engine get rid of the full exhaust charge and limits the amount of air the intake stroke can suck in. Gota get it out before you put more in. Other wise you just recycle the exhaust. Less air in means nothing for low power as you are always sucking in more than you need. At FULL POWER the intake manifold is operating at full capacity to deliver the correct amount of air for a FULL POWER fuel charge. Any restriction in the intake or exhaust will limit that air charge and result in unburned fuel due to the lack of O2 entering the engine.

A muffler full of water or the actual exhaust plumbing that requires a high lift of water to get it over the anti-siphon loop would be just such a gremlin. Ain’t there at low power and only shows up after a while at full power. Then goes away when you throttle back. FWIW

 

[Bill Roosa]

Diesel basics 102a

The oily residue in the exhaust would indicate the not only is there not enough O2 to burn the entire charge but there is not even enough to partially burn some of the charge and it just enters the exhaust as liquid fuel. A poor spray pattern (drips) could cause that also. I would suspect that the poor spray pattern would be present all the time as the injectors don't spray more fuel per time period for more power they spray longer at a fixed rate. so they always have the same pressure and just stay open longer when more power is asked for.

Oil coming out the exhaust is probably not engine lube. Rings leaking cause exhaust to come out the crankcase breather tube and enter the intake manifold not engine lube to show up in the exhaust. Pull the crankcase breather hose off at full power to confirm the amount of blow by. A blown oil ring (bottom ring of the set) will allow engine lube to get into the combustion chamber but then you are talking about a run away engine due to the lack of being able to shut off a supply of fuel, in this case engine oil.

 

[Terry411]

For the cold start problem. Try a dipstick heater if you have shorepower. Cold oil glues parts in place. Try turning a cold engine vs warm by hand.

 

[RAD]

I bought heating pads that are epoxied to the oil pan on my diesel truck and they worked liked a charm you would get in the truck and the temp gauge would be warm...I thought I could install one on the boat but it wouldn't slide under but maybe you have room

 

[COOL]

Sounds like it is time to convert to electric propulsion.

 

[Hermit Scott]

Diesels do not have fuel air mixtures. ....They squirt the fuel at a precise moment at the top of the compression stroke

The air and the fuel don't mix in a diesel??? I have never heard that from anyone.

There is no one particular moment of injection. It is over a number of degrees turning of the engine.
As you say here "just stay open longer when more power is asked for"
There is no "moment" of injection. There is only a moment of beginning and a moment of ending of injection.
Also if an engine is hot it will burn a poor spray pattern better. When it is cold it burns a poor spray pattern poorly. Those are all facts.
But I suspect that all the fuel is injected before TDC so there is an even burn when the compression brings the air/fuel mixture to the ignition temperature, I am just guessing at that though. It would seem inefficient to me to inject fuel after TDC. If anyone knows that for sure I would appreciate the lesson.

 

[Stephen Trapani]

For the cold start problem. Try a dipstick heater if you have shorepower. Cold oil glues parts in place. Try turning a cold engine vs warm by hand.

All these fancy ideas and all he probably needs is a stronger starting battery IMHO. He said it was spinning slowly when he tries to start it. It's a small diesel motor. A powerful CCA battery will spin the dickens out of it, cold or no. Worked for me.

 

[Steve Dion]

Get your battery charged & load tested.

Put a couple of Golden Rods in your engine compartment and plugged in during the cool months.

Follow the advise regarding the shut down procedure.

 

[Stu Jackson]

and check your engine ground, it may not be the battery.