White Smoke from Engine

[Steve S.]

I have a 1988 MX-25 with about 650 hours.

I've been getting white smoke all summer when running the engine at about 1600 rpm and up.  I've read past posts and most people believe that white smoke is steam from poor raw water flow.  But I don't think that's it. 

I think it may be from something else.  For whatever reason, the engine just doesn't push me as fast as it used to.  I probably hit 5.5 knots on flat water with no current, it used to hit 6.2.  While the engine revs to 3000 while in neutral, I'm lucky to get to 2000 rpm under load.   I've read in other past posts that getting lots of white smoke at hi rpm is caused by too much fuel and poor combustion.  I tend to think that's it.

I did change the motor mounts and the cutlass bearing last season but that shouldn't affect performance.  The shaft seems to turn easily.  (It does run smoother with the Vetus motor mounts.)

The question I have is what can I do about poor combustion short of a ring job?.  Also, do folks think a tinkering of the valves may help?  The engine runs smoothly and don't hear any pinging that would be associated with bad valve seating.   

Thanks

[Jeff Kaplan]

steve, white smoke, not steam, is usually a sign that you are burning oil and that leads to a ring job. check the oil level to make sure you're not low. there are additives that claim to reduce oil burn but they are just a bandaid. when in doubt, bring in a diesel mechanic. he will do a combustion check and a few other tests to determine exactly what is causing the problem. you don't need a marine diesel mechanic to do the work. remember a diesel engine is a diesel engine, whether in a boat, car or truck. only difference is we cool with raw and fresh water...jeff

[Jeff Kaplan]

steve, in my last post i said a mechanic would do a combustion test, i meant a compression test. worn rings will cause a loss of power as full combustion is not taking place...jeff

[Ron Hill]

Guys : Anytime you have a mechanic run a compression check - make damn sure the raw water thru hull is turned OFF!!  Otherwise you'll fill up the muffler and the raw water can/will flow into the cylinders.  This will screw up the engine - big time!!

[Jeff Kaplan]

ron, an excellent point to have brought up...jeff

[Ray & Sandy Erps]

My experience has been that white smoke is unburned fuel being expelled through the exhaust.  White smoke when a cold motor first starts up would not alarm me much.  Just watch a highway truck start up on a cold morning and it spews white smoke.  It should clear up as it warms up though.  Is your motor reaching operating temperature?

If it's steam, it should disappear/dissipate shortly after coming out the exhaust fitting.  If it's smoke, it will hang around longer.  Also, if it's smoke, I would expect that if you held your hand in it, you would be able to smell the fuel after a big of it has condensed on your hand.

If it was my motor and I was able to determine that it is smoke and it's associated with low power I would start to suspect a dead cylinder, either due to compression or an injector that's squirting un-atomized fuel.  I would start by doing a poor man's compression test.  Crank the engine while the fuel shut off cable is pulled to see if you can hear uneven compression.  If the compression sounded even, I would start up the engine and start cracking injector fuel nuts one and note the effect on the engine.  That's like pulling spark plug wires and listening to the RPM's decrease.  If you don't hear a noticeable decrease in engine RPM after cracking one injector fuel nut, I would pull that injector out and inspect it for damage.

If the compression sounded uneven while cranking it with the fuel shut off pulled, I would start trouble shooting the reason.  It's most likely valves or rings.  Blue smoke is associated with bad rings, so I would look at the valves first.  I would check the valve lash to see if any of them are tight.  If they're within specs and the springs looked good, I would begin to suspect a valve leaking past the valve seat.  I might try a real compression test to confirm it or just pull the head off and check.

One other source of white smoke that I've seen before is when antifreeze is getting in to the cylinders.  It also leaves a sweat odor in the exhaust.  This is a bit unusual, because typically if you have that kind of a head gasket leak, the compression will get into the coolant circuit and blow the fluids out, but still, I saw it once or twice on highway trucks.

Anyway, that's where I would start troubleshooting. 

[Ron Hill]

Steve : Ray's analysis is "Right ON". 

[Jeff Kaplan]

steve, just spoke to a diesel mechanic friend of mine and he agrees with ray that it probably a bad injector nozzle, not bad rings as i had suggested. as ray stated, run the engine and crack, loosen, the injector nuts, one at a time, and listen for a skip. that will be the bad one. what's happening is that the fuel is not being atomized. good luck...jeff

[Steve S.]

Thanks guys, especially to Ray - I have spoken to a mechanic.  I still plan to have him do a compression test as I have not had the engone checked out for quite a while.   But I can do these preliminary tests first.  The injector test is especially interesting.   When I accelerate, I can only go so far, which leads me to believe that the injectors could use cleaning.  Hopefully, it will be that simple.   

[lucky]

 Steve
I was an over the road mechanic for caterpillar dealers for 40 years working tractor an marine engines.Ray has given the best advice yet.Break those fuel lines and listen for sound for change.Remove oil filler cap and look for blow by.
post what you find
Al
lucky
1986 hull #13

[Dave DeAre]

Steve,
I had a similar problem on a 25 XP and it turned out that the screen on the bottom of the air cleaner cannister was partially blocked with metal particles from the mesh filter element. This may be a long shot, but check the air cleaner and screen before doing something more drastic.
Good luck!
Dave

[Ron Hill]

Steve : You can go by your local Kubota dealer and purchase a new set of injectors.  They'll cost about $60 each, but are easy to change and your 20+yr old engine deserves them.  I wrote a couple of Mainsheet tech note articles on how to change them. 
You'll be surprised at the increased performance.

[Steve S.]

Ron - not a bad idea, even if I wasn't having this problem.  Sounds like a good maintenance "upgrade".

Thanks 

[David Sanner]

Ron, I had my injectors bench tested when I rebuilt at
about 1800 hours.  (My engine is also 20 years )

The tech said they were fine but I've always wondered
if I could do a little better with new ones and get rid of
some of the black dirt on the transom or in the water
at the dock when I run it hard.  Seems to idle fine but
I've set it at at least 1000 rpms.

I always wondered how well they could test just
by looking at it.  Do you think new ones would help?

I figured it's either that or my injector pump isn't
putting out as much pressure as it should...
(Twice now my engine has lost significant rpm, still
chasing that one down... might be the wiring on fuel
pump or maybe the injector pump is going.)

[Ron Hill]

David : I found that the cost of rebuilding and new injectors are nearly the same.
I believe that the bench test is valid - you look at the pressure that they "pop" at and the spray pattern they emit.  If both of these check out - things should be OK.
I found that my injector pump was bad - engine had no power.  The internal shinny smooth internal parts were crazed and dull.  Don't know how that happened and the guys that rebuilt it had never seen anything like that before?  Good Luck.