Low RPMs and Smoke

[Charlie]

Hi everyone am bringing the boat up from Cabo to La Paz after the Baja Ha Ha. Have limited wifi so can't research very much. here is the scenario --- new engine (540 hours and well maintained) Yanamar 4JH4E. Had a problem with wihite smoke in turtle bay polished the fuel and everything is better. While polishing fuel found lots of crud in the fuel. Seems to work fine as long as I keep it under 2k rpms.

new problem.Get the engine over 2000 RPMS and the engine begins to race and then the exhaust fills with blue smoke. hard to kill the engine. If we lower the RPMs below 2k the engine runs fine. No changes to the engine but I did put a 6" extension on the exhaust. Any ideas what could be causing this? Injectors? Timing? Valves? I have a theory that oil is somehow causing the engine to race but have no supporting data. Any ideas would really help. Please give me things to check.

[jdoe71]

That sure sounds like oil getting into the combustion chambers from somewhere. I take it there's been no noticeable drop or increase in the oil level? Do you have a crankcase vent that is routed to the air intake? Is it really oily?

[shakey doug]

Hi Charlie,
Check oil level & test for fuel dilution also look around air intake for possible fuel source such as leaking over head fuel tank or pipe work etc. undo each injector in turn, each cyl reaction should be the same if not possible dicky injector also undo fuel return line &test at revs for possible blockage. Cheers, Doug.

[Charlie]

Thanks guys I will try those.

[Chief Engineer]

Check for overfilled oil....may have a fuel lift pump that has gone bad.....

Overfillling is very common on yanmars due to the seal on the dipstick.

To check oil...pull dipstick, wipe off, push stick in and then pull out slightly past rubber seal then push stick in and then pull out to read level. Some engines have a tube that goes to the bottom of the oil pan.

[wsvoboda]

I have a blue smoke problems to. seems my 109.00 dollar Yanmar manual states that if exhaust color is bad to check the following.
1. Load unsuitable, chech the propeller size.
2. Fuel injection timing off.
3. fuel is unsuitable.
4. injection valve faulty
5. intake and exhaust valves leaking.
6. OK that's was enough for my take since you have polished the fuel please make sure you have changed out your fuel filter(s) and purge airlocks in the engine fuel system. I have run my Yanmar up to 3000 RPM's with the blue smoke for over an hour and the engine never overheated and I lost very little oil I'm talking 1/4 cup of oil for 30 miles of running. The Yanmar is a very foregiving diesel and will take you to hell and back.

[Örjan]

check your oil level. Is the oil level increasing? Is it running on all cylinders?

I had a similar problem, was a leaking seal in the high pressure fuel pump (injection pump).(expensive) It filled the crank case with fuel and it came in to the combustion chamber(s) through the breather pipe in to the intake. This caused the engine to race and a huge cloud of white -blue brown smoke came out. keeping it under 2000 rpm it occurred less times. Took me a long time to solve this.
Had the injection pump repacked, solved the problem

Hope this helps you.
First check if your oil level is increasing., If not then you have an other problem.

[Örjan]

The racing can not be caused by (at least not to my knowledge) by oil but by fuel therefore I suggest fuel in the crank case.
It can get in there also through a leaking lifter pump (broken membrane )(it has a connection through the crankcase since it is getting its motion from the cam shaft. that is valid for the 3GM30F. I do not know about yours)
but then I guess you would have problem getting enough fuel to run the engine proerly.

Hope this helps.

[imagine2frolic]

Could it be something as simple as the air filter?......i2f

[mike d.]

oil getting in the cylinders will most certainly cause an diesel engine to speed up because it is un-metered fuel. if it gets bad enough the engine will run away/over rev and blow up!!!!!

[Chief Engineer]

Overfilled oil level

Blown Turbo seal

Blown Blower Seal (Detroits)

There are some others that can occur in BIG ENGINES like Tugs
(We called it a base explosion where the fumes in the crankcase "light off" and the fumes get sucked into the engine) I had this happen on a Fairbanks-Morse Ten cylinder Opposed Piston Diesel.....Fortinately there was a lot of redundancy in the shutoffs

Originally Posted by Örjan

The racing can not be caused by (at least not to my knowledge) by oil but by fuel therefore I suggest fuel in the crank case.
It can get in there also through a leaking lifter pump (broken membrane )(it has a connection through the crankcase since it is getting its motion from the cam shaft. that is valid for the 3GM30F. I do not know about yours)
but then I guess you would have problem getting enough fuel to run the engine proerly.

Hope this helps.

Originally Posted by mike d.

oil getting in the cylinders will most certainly cause an diesel engine to speed up because it is un-metered fuel. if it gets bad enough the engine will run away/over rev and blow up!!!!!

[delmarrey]

Originally Posted by Chief Engineer

There are some others that can occur in BIG ENGINES like Tugs
(We called it a base explosion where the fumes in the crankcase "light off" and the fumes get sucked into the engine) I had this happen on a Fairbanks-Morse Ten cylinder Opposed Piston Diesel.....Fortinately there was a lot of redundancy in the shutoffs

Hey Chief..Is that you up there on that big motor.

[Charlie]

here is a quote from the manual. " The engine oil should not be over filled to exceed the upper limit line. If engine oil is overfilled, the engine may intake the engine oil in the combustion chamber during the operation , and white smoke, oil hummer or urgent rotation may occur, because the blowby gas is reduced in the suction air flow." I laughed when I read that. it is exactly what was happening to me. So then I found a table that had two different amount of oil to put in the engine. One for a flat engine and a smaller amount for a "rake angle " engine. Yes mine is the rake angle. Then to compound matters I guess the suction pump that I use to remove oil from the boat doesn't get all the oil out of the engine and though I have been removing the oil and adding more than I was supposed to well . . . . it should suffice to say I am a horses ass and have figured out things anyway. LOL

Thanx for the comments everyone. I hope this has solved it but I will look for increasing oil level. Is there anyway to check if there is diesel in you oil. can you put the oil in a clear bottle and will the two seperate?

[delmarrey]

Originally Posted by Charlie

Is there anyway to check if there is diesel in you oil. can you put the oil in a clear bottle and will the two seperate?

The viscosity & smell should give it away. For a reasonable time of separation, you would have to put on a centrifuge. Or you could send it to a lab, which are getting fairly reasonable theses days. A lab could give you a PPM (%).

[Charlie]

I'll see if I can get it home to send off to a lab. Thanks Del