Yanmar 2QM15. Putters along at low revs with a spray type water flow out of the exhaust. Not much smoke. (Would like to post video, but it is more than 20mB. ) Increase revs to about three quarters, and vast quantities of white smoke? billow out of exhaust. What does the brains trust think is the problem? Water pump? Inlet strainer? Leaking head gasket?
At moderate revs, top of motor is at around 60 degrees C, exhaust manifold and most other areas around 45 degrees,

Low speed:
High/medium speed:

I have the same model engine in a 30 footer.
You have a Top Hat 25 don't you? It is certainly pushing her along allright.
General rule is :-
Black smoke = over fuelling or overloading.
Blue smoke = oil bypass.
White smoke = water in the combustion ie head gasket or cracked head.

With these engines, because they have wet cylinder liners, removing the cylinder head just about dictates a full rebuild. Not cheap for Yanmar parts either.

They are about 30 years old but when they are right they will pretty much go forever.

A possibility is that you may have water in your fuel. If that is the case it is an easy fix but one that needs to be done urgently before it buggers your injection pump and injectors.

If there is water in your primary filter bowl you will need to sort that by draining your fuel tank changing filters and bleeding the system. It would also be worthwhile pulling your injectors and taking them to a marine injection shop not an automotive injection shop.

More info about your engine set up would help.

I'm definitely no engine expert but heading down to Tassie last year I was doing an overnighter and the engine seemed to drop revs and miss briefly and then began belching a large amount of white smoke. Thought I had broken something serious but checked oil, cooling, cylinders, everything and could not find anything wrong to explain it. Eventually got in the water and found a bunch of kelp wrapped around the prop, once that was cleared it went fine and no more smoke. Could be worth checking before the more expensive options!

Yes I would check the prop first. When was it last cleaned/prop speeded?

No, I would check the water trap bowl of the primary fuel filter first. You don't have to swim to do that.

It is in a Compass 29 I was doing a pre-purchase survey on. At half throttle she was doing 5 knots in calm water with little wind.

Inspected the prop from the surface with a inspection camera. Not easy to see a small screen in bright sunlight, but the prop was reasonably clean with just a few small barnacles. Boat was anti-fouled about 10 months ago. Has been used as a live-aboard, and the engine was run occasionally to charge the batteries. Not loaded up for some time, but regularly serviced by the marina.

There is a plastic tube sight gauge for the fuel, and no water seen. Did not check the engine oil after the run. It was a hot day, and the octogenarian owner and I were struggling with dehydration and fatigue!

Owner will ask the marina to have a look today.

Select to expand quote

cisco said..
No, I would check the water trap bowl of the primary fuel filter first. You don't have to swim to do that.

what he said urgently

Select to expand quote

Yara said..
It is in a Compass 29 I was doing a pre-purchase survey on.

Is that Orion ?

With that much steam in the exhaust smoke you have either a cracked head or leaking head gasket. My Yanmar 3QM30 had the same symptom though not as much steam as in your video clip. The engine ran well like this for a few years until left without use for six weeks. The engine was seized and subsequently replaced.
If you really like the boat I would negotiate the price of a head rebuild off the final price; otherwise buy something else as there are a lot of great buys available on the market.

Looks like smoke to me, not steam, I would do as others have said, check water separator and fuel tank, check prop then oil level and viscosity and if all good then perhaps an Italian tune up. (good hard run to free up any sticky rings and burn off any residual oil in the manifolds) Need to make sure it is smoke and not steam first.

I'm certainly no expert, but from the video I don't think you've enough cooling water flow, and the 'smoke' could be steam.
I had a similar symptom a while ago and it turned out to be the primary raw water filter (inlet strainer) extensively blocked with sea grass.
Here's hoping....
regards,
allan

Agree with all the above. If it appears to be caused by gunky stuff on rings/valves etc try FTC in the fuel. Really good stuff.

Select to expand quote

Datawiz said..
I'm certainly no expert, but from the video I don't think you've enough cooling water flow, and the 'smoke' could be steam.
I had a similar symptom a while ago and it turned out to be the primary raw water filter (inlet strainer) extensively blocked with sea grass.
Here's hoping....
regards,
allan

Yeah, doesn't seem to be enough water flowing though - intake filter blocked or the engine needs an acid flush to clean the water passages. might even be the exhaust elbow/mixer blocked.

Select to expand quote

Lazzz said..

Datawiz said..
I'm certainly no expert, but from the video I don't think you've enough cooling water flow, and the 'smoke' could be steam.
I had a similar symptom a while ago and it turned out to be the primary raw water filter (inlet strainer) extensively blocked with sea grass.
Here's hoping....
regards,
allan

Yeah, doesn't seem to be enough water flowing though - intake filter blocked or the engine needs an acid flush to clean the water passages. might even be the exhaust elbow/mixer blocked.

+1

no1 ,do what cisco said and check for water in the filters.
if ok check weather it is steam or smoke .
if there is water in there i think it will need new injectors as a minimum
if it is steam you need to repair the water system for blockage or faulty pump .
if its white smoke it can be a number of issues ,
UN burnt fuel will cause white smoke which can be any of the following cracked head or ring s lowering compression. water entering combustion ,failed injector spring,over heated motor.
you Reilly need to get a professional to look at this motor and diagnosis it correctly .

you did not buy the boat yet right? If so, pay for an engine pre-inspection check.
If you already bought the boat (congrats) my bet is possibly just water in fuel, drain (from filter housing too) and replace fuel.
Run it again, and see how it goes. No need to cry wolf just yet.
But, you should definitely have a pre-filter for water intake and I would recommend replacing the original filter housing with a new water separating filter.