Volvo 5.0L V8 - starts out of the water but not in...?!?!

[Freeloader]

Unfortunately, I can't provide much technical information here as the offending article is not my boat! However, the motor (a Volvo 5.0L 270hp V8) is fitted to a Rinker 246 (I think of circa 2008 vintage) and has the duo-prop sterndrive. Whilst the motor will apparently start perfectly well on the flush muffs, when put in the water (the boat is on a dry stack) it simply will not start. Two separate marine engineering firms have played about with it and changed one or two parts but said that they can otherwise find nothing wrong with it - (on land) it starts and runs fine.

Indeed, subsequently it was started on the muffs and then dropped into the water but then failed to start. However, when lifted and held just above the water by the fork-lift, it started and when dropped back into the water (still running), it ran around fine for a couple of hours (without stopping the engine). The engineers from both firms and the owner are at a loss to know what to try next. Could there be some sort of grounding issue when the boat is put into salt water???

Any advice or suggestions would be gratefully received!


N.B. We are keen to sort this out, not least because we are supposed to be meeting up with our respective boats and families next week...

 

[[2068]]

The main difference between in the water and out, will be that the exhaust back pressure is higher when in the water.

So if compression were marginal, then being in the water might be enough for it not to start ...
... but you say the engine ran ok when dropped in after starting, which doesn't make sense
Might be worth taking plugs out, check compression, check for water inside cylinders.

 

[oGaryo]

It may (big may) have something to do with the attitude of the boat i.e. when in the slings or on the hard it'll tend to sit level, when in the water, that may change. I'd go back to basics when in the water and check for the like of fuel flowing ok to see if there's a blockage or air pocket with the boat sitting at a certain angle. Have you checked the float in the carb to ensure it's adjusted properly?

 

[dpb]

The main difference between in the water and out, will be that the exhaust back pressure is higher when in the water.

So if compression were marginal, then being in the water might be enough for it not to start ...
... but you say the engine ran ok when dropped in after starting, which doesn't make sense
QUOTE]

Or if the battery / starter motor were marginal?, enough power to spin and start without back pressure, but not enough when working against it?...That would explain running OK if started before being put in the water may be?

 

[P4Paul]

The main difference between in the water and out, will be that the exhaust back pressure is higher when in the water.

+1 based on a similar experience. Had an outboard that ran perfectly on muffs but would not start in the water, tried everything I could think of. Finally I bit the bullet and stripped it down to find a cracked ring. Replaced the ring and the problem was cured.

 

[Freeloader]

Thanks for all the very quick replies. I know that it's very difficult to diagnose problems remotely but was just hoping that someone might have suffered the same sort of problem and might be able to point us in the right direction

As far as I am aware, the engineers were not on site when he tried the fork-lift start and so the problem has always been tackled with the boat out of the water. As has been suggested, perhaps the exhaust back pressure is an issue in the water or, maybe, a blockage in the fuel supply that is affected by the angle of the boat. Probably the best thing to do now would be to put the boat back in the water and get the engineers to test it there to help diagnose the problem.

 

[tinkicker0]

Check that your high level exhaust ports on your transom shield have not become blocked, otherwise the exhaust can only go through the prop centre and will cause too much back pressure for the engine to start when in the water. On the muffs the cooling water should exit the transom shield area, not the prop. No water exit high up and your ports are blocked with shellfish or something.

 

[GrahamHR]

270 HP, That's a fuel injected 5.0 GXi.

For issues relating to petrol engines you should post your question on an American forum like something like iBoats. If there is any experience with this particular problem on an American boat, then it will have shown up in the US where petrol powered boats are far more common ( and strangely, don't blow up that often despite the dire warnings on this forum!)

 

[lovezoo]

( and strangely, don't blow up that often despite the dire warnings on this forum!)