white smoke/steam/black smoke

[BOBBIN]

Yanmar 3HM35 raw water cooled engine shows steam/white smoke from exhaust increasing with revolutions.
Engine does not overheat.
Have replaced water pump, thermostats and water passing through anti syphon loop seems to be at moderate temperature with good flow.
Exhaust mixing elbow was removed about 12 months ago and carbon ground out of gas and water entrances.
Is it possible that this steam is caused by water/gasses not mixing properly? Or is there an alternative answer?

Although the engine starts first time, there is some evidence that the fuel supply to the injectors is not correct as injectors have been removed,checked and tested and replaced and black smoke is seen when putting engine under heavy sudden load. This disappears completely when revs are reduced.

Could these two problems be connected in some way? Is the steam not steam?

 

[Salty John]

I would suspect a leaking head gasket.

 

[steverow]

This is almost certainly a faulty head gasket.
Water is getting into one or more of the bores.
Get head off, skim, do valves and seats and refit with a new head gasket.

Steve.

 

[ZEBEDEE]

Have you done the simple thing and checked for water in the fuel. This would cause white smoke, and mess up your injectors, if it had got past water seperator. White smoke would also increase with revs.

 

[davidpbo]

Check for beige coloured emulsion on oil filler cap.
May be another sign of blown head gasket.

David

 

[andy_wilson]

This is a lmost a copy of another reply, apologies for the replication, I have changed a couple of points to suit.

Black smoke is excess carbon particles due to unburned fuel due to poor breathing or overloading engine. Typical culprits are blocked air filter or air intakes or new engine room insulation, or collapsed / delaminated exhaust pipe. Also, fouling on hull or prop. In extreme, gearbox or shaft bearing problem. In your case, as you open up the throttle, the fuel rack advances quicker than the air supply (revs.). Once the engine is up to speed, the black smoke should subside, unless of a problem hi-lighted above.

Blue smoke is usually oil so you're OK on that.

White / grey smoke can be steam OR, if it smells rank, it could be unburned diesel due to a poor injector dribbling it in rather than spraying. Water is unlikely (but not impossible) to be getting into the cylinder of a raw water cooled engine. The compression within is far far greater than the pumped water pressure. Is there any sign of combustion gasses within the boat, for instance around the syphon valve? Is there any sign of emulsification of the oil due to water finding it's way into the oil system. Oil well used in this state will thicken, and a creamy coating will settle inside the rocker gear typically. If the oil looks OK....

The cylinders will carbon up if they don't get a good blast now and again, and this can coke up the injectors too, causing a poor spray. It's worth running her hard for 10 - 15 minutes to blow it all out. Then see how it is afterwards. This is a non-invasive attempt at a cure.

If you are handy, and the design allows it, pull the injectors and re connect the wrong way round and turn her over on the starter. A good injector will fire pulses of fine mist. They need a service if they dribble or squirt a jet (which you should beware of, so keep your distance whilst observing). This is slightly less invasive, but an easy DIY check.

An alternative is to find a back street MOT centre and ask them for a bottle of whatever they use to get a marginal diesel motor through the MOT emmissions check. Half fill the engine fuel filter with it, put the rest in the tank, bleed through and run her on that for a bit, to see if that improves things.

 

[Guest]

Just a few rules that have served me well:

White smoke that disappears somewhat when the engine is warm is unburnt fuel. Caused due to bad injection pump timing or injector pressure settings/damage. Injectors can drip excess fuel out side the time it should spray. Or the pump sprays the fuel into the cylinder before the optimal compression.

Too much steam (white smoke) is due to too little cooling flow or mixing. My engine produces a little steam at idle. Seen on many boats due to tapping off other water supplies from the same sea cock. Air can be sucked back through the other systems and reduce the engine pumping ability. Only normally seen at low revs when the pump is seeing to much air. However, if the inlet seacock is restricted it will get worse for higher revs. Sit in your cockpit on a weekend and compare your water flow with the other boats. You can always hold a bucket under the output for a few seconds and measure the flow rate. Also I did find one boat with a failed thrust plate in the back of the water pump that was rotating.

So the key is to find out which. Smoke lingers longer, if your neighbour is complaining it is not steam. On a windless day you should be able to see the difference at idle.

Water in the fuel should not occur with a separator. If it does, it will ruin the injector nozzles.

Any head gasket problems will show up as undue pressure in the sump or water system. It all depends if the head gasket has broken through into the oil or water lines. In a raw water system you would see large amounts of air in the water going to the siphon break. I saw an engine in Panama that literally blew water out of the expansion tank on every revolution when we removed the cap. But he had just filled the cylinders with sea water due to the extra weight of the canal line handlers in a 30' yacht and a blocked anti-siphon valve.

Black smoke at high revs is overloading of the engine and should just occur if the boat is set up to use the full engine output. Do not run it like this though, back it off a bit. More easily produced when tied to a dock as the water is not moving initially.

Blue smoke means the oil has got lost and is entering the pistons. Valve seals normally, but rings and head gasket as well.

 

[vyv_cox]

I haven't heard of this with a raw-water cooled Yanmar but it is very common with Bukh 20s. Do a search on this forum and you will find considerable correspondence. The steaming in this case is not an indication of an engine problem but some phenomenon to do with the relative proportions of water input and exhaust gas temperature. The Yanmar water throughput is greater than with the Bukh so I suppose the staeming to be less likely. However it could be a consequence of your installation. You could usefully check the area of water input to the engine from the pump, on the Bukh this salts up quite badly.

Unless your engine shows unmistakeable signs of distress, e.g won't turn over due to water in compression space, water in oil, etc I would do nothing drastic.

I don't see how the black smoke can be in any way connected to the steaming proiblem - simply a consequence of unburnt/partially burnt fuel under load.