White Smoke but Engine Runs Fine

[Artessa]

We've got an '83 Yanmar 2GMF. Last year the engine started showing white smoke. A guy from the yard said replace air filter. When I did that (the old one was pretty clogged) the white smoke all but disappeared. This spring on the first cruise the engine started belching black smoke at about 1800 rpms and wouldn't accelerate further. After it ran for a while the problem stopped but the engine has continued to put out a fair amount of white smoke (I'm assuming it's white smoke and not steam -- I can put my hand on the antifreeze filler cap after the engine's run for a half-hour or so, which I assume means it isn't overheating.) Water is coming out of the exhaust although not in particularly large bursts (I never paid much attention to the volume in the past so I can't say whether the current output is significantly different)

The engine starts and idles easily and runs very smoothly even at higher RPMs (although I never take it higher than about 2200) The black smoke has not reappeared.

Any ideas?

[Chief Engineer]

White Smoke is either water

or totally unburned fuel

[Artessa]

My sense is that it's unburned fuel as I can smell diesel fairly strongly when I stick my head over the stern. Could the unburned fuel thing come from bad gas?

If it is steam wouldn't the engine be running hot?

[mesquaukee]

If the exhaust smells strongly of diesel then you could have a faulty injector or more likely low compression in a cylinder. The fuel doesn’t burn if the pressure (temperature) is not high enough to ignite it.

[Chief Engineer]

There are somes tests that can be run.

Are you handy with a 17mm wrench?

[thinwater]

Originally Posted by mesquaukee

If the exhaust smells strongly of diesel then you could have a faulty injector or more likely low compression in a cylinder. The fuel doesn’t burn if the pressure (temperature) is not high enough to ignite it.

11111

[Artessa]

I'm pretty handy with most wrenches, 17mm included but fairly new to diesels (If you've got any Atomic 4 questions and I'm your man!) What tests do you suggest?

A quick question about the stuck injector idea... if I had injector problems the engine would be running rough right? It starts and runs very smoothly.

[Chief Engineer]

Before starting the engine, make sure you can crack the injector nuts loose.
With the nuts tight, start the engine.
Loosen one nut and notice rpm drop
Tighten and loosen the other nut.
This will tell you if you have a problem with one or the other cylinder.

Report back with your findings

[TOM]

Is it white smoke or blue {suttle difference}I thought i had white smoke but turned out to be blue are you using oil?

[Artessa]

OK, before I do any loosing of injectors I need to know how much to loosen the nuts. Also not to be paranoid but I've heard all sorts of stories about the possibility of fuel coming out of lines at enormous pressure when you mess with the injectors. As I said, I'm new to diesels so I have no idea if this is even a possibility when I do what you're asking.

As for the blue vs. white smoke, I'm pretty sure it's white. As far as I can tell I use no oil although I only run the engine about 15 hours a season (sailboats are for sailing!) so it's hard to tell what would happen over a longer period.

I'm 2.5 hours from the boat and won't be able to get aboard for a week or so, so it'll be a while to get back on this. Chief Engineer, will you continue to monitor the thread so I can give you the results?

One last question. I'm in Maine and the season for us only runs until the end of Sept. If I discover that there is a compression problem am I running any risk to keep using the engine until I get her back on the hard?

[RBEmerson]

White smoke with no diesel smell is the sign of water getting into the engine through a bad head gasket or cracked head or block, in descending order of ugliness. Is there a sheen of oil in the water around the exhaust? That points to unburned fuel coming of the exhaust.

That the engine wouldn't turn past 1800 (very odd for a Yanmar) and smoked heavily, and now it turns 2200 but produces white smoke suggests fuel problems that could be anywhere from a problem with the high pressure pump to the injectors. Given how little the engine is used, and given its age, I'm betting that seals have started to break down and gum up the injectors. Again going back to the age of the engine, I'd just bite the bullet and have the pump and injectors rebuilt, instead of guessing and groping. With a good mechanic and a bit of luck, this shouldn't take more than a week to ten days, start to finish.

However, you really, really, really need to nail down what that white smoke is. I wonder if you aren't looking at two problems: fuel and cooling. It's not enough to just say "yep, coolant cap's cool". Have you checked to see if there's any sign of coolant loss? What does your temperature gauge say? When was the last time you replace the raw water impeller? How's the belt tension? All of these could be factors in the engine running hot and steaming, not smoking.

[rtbates]

One of the worst things you can to a diesel is NOT USE IT.... Whenever you use your diesel use it long enough for it to get up to temp and put a load on it.... A good way to kill a diesel over time is to use it for 10 minutes every time you come and go and nothing more. Or let it idle without a load for long periods of time. IT AIN"T A TRUCK!!!

[RBEmerson]

Amen and amen!

[gs41escapade]

Given the strong diesel smell in the exhaust, it is most likely a stuck injector. Does the engine run rough -- i.e. missing cylinder? I have never done it, but the test of cracking injector nuts to see which one DOESN'T change the engine's run seems the right next step. I believe the purpose here is just to relieve the compression on the cylinder, so you should only have to crack the nut one or two turns at most. Keep something handy to catch the little flow of diesel that sill back out along the fuel line.

[RBEmerson]

Originally Posted by Artessa

OK, before I do any loosing of injectors I need to know how much to loosen the nuts. Also not to be paranoid but I've heard all sorts of stories about the possibility of fuel coming out of lines at enormous pressure when you mess with the injectors. As I said, I'm new to diesels so I have no idea if this is even a possibility when I do what you're asking.

You're quite right to be concerned. Injector fuel pressures are on the order of a few thousand PSI (varies from engine type to engine type - some new systems hit five digit pressures!). However, you can back the nut off maybe a 1/4 or 1/2 turn (with a rag around the area to contain the leak) without too much worry.

As for the blue vs. white smoke, I'm pretty sure it's white. As far as I can tell I use no oil although I only run the engine about 15 hours a season (sailboats are for sailing!) so it's hard to tell what would happen over a longer period.

See the "it ain't a truck" comments. Diesels need to be run at full operating temperature to be happy. Anything less does nothing good for them.

[...]

One last question. I'm in Maine and the season for us only runs until the end of Sept. If I discover that there is a compression problem am I running any risk to keep using the engine until I get her back on the hard?

Yes, you are. It's not so much the loss of compression (not good) as not knowing why compression is off. Given the light amount of use, it's probably not cylinder wear that's getting your engine but something else. And none of them are good news.

However, without doing a compression check (you must use a diesel compression tester - most gas compression testers won't take the pressure), the idea that you're loosing compression may be just a guess. Having the check done is a good idea, though.