Volvo penta MD6A will not rev past 1600rpm under load.

[cptpugwash]

Volvo penta MD6A will not rev past 1600rpm.

My volvo penta md6A engine will not rev past 1600rpm there also appears to be a film of oil coming from the exhaust onto the water and black soot on the transom, the engine oil level doesn't change.
All filters have been changed, the prop and underneath is clear of marine growth, I believe that this engine should rev up to 3000rpm.
Does anybody have any ideas to this problem.

 

[RobinBirch]

check for blockages at the exhaust elbow and for delaminated flexible exhaust hose

 

[Seajet]

What boat, what load, not just design but conditions; is the exhaust outlet cooling OK as the previous poster mentioned ?

 

[cptpugwash]

check for blockages at the exhaust elbow and for delaminated flexible exhaust hose

Thanks for that i will check the elbow and flexible hose this weekend.
Regards cptpugwash.

 

[cptpugwash]

What boat, what load, not just design but conditions; is the exhaust outlet cooling OK as the previous poster mentioned ?

Hi there, the boat is a westerly 22 the cooling seems to be fine, it will rev up to 2800rpm out of gear, when under load the engine doesn't miss a beat and starts at the first click of the key.

 

[Tranona]

Has it always been like this? Symptoms suggest prop is too big.

 

[mitiempo]

I second the exhaust elbow. Engines need good compression, clean fuel, and good breathing - both in and out. The exhaust elbow is ignored by many until the symptoms you are having occur - many times they find the exhaust elbow is restricted. The oil film and carbon you see on the transom is coming from unburned fuel.
This assumes the correct prop in clean condition and a clean hull.

 

[cptpugwash]

Has it always been like this? Symptoms suggest prop is too big.

No everything seemed to be alright but there has always been a film of oil coming from the exhaust even on tick over with the engine out of gear.

 

[Tranona]

No everything seemed to be alright but there has always been a film of oil coming from the exhaust even on tick over with the engine out of gear.

Are you saying that it used to rev to 2800 in gear but now does not do that? If it has never reached near full revs the prop is wrong.

If revs have fallen away (and speed with it) then the suggestions re exhaust elbows and blocked exhaust hoses are sound. The oily film is common on many older engines, particularly if they have not been worked hard, but black smoke and soot is usually a sign that the engine is overloaded.

 

[cptpugwash]

Are you saying that it used to rev to 2800 in gear but now does not do that? If it has never reached near full revs the prop is wrong.

If revs have fallen away (and speed with it) then the suggestions re exhaust elbows and blocked exhaust hoses are sound. The oily film is common on many older engines, particularly if they have not been worked hard, but black smoke and soot is usually a sign that the engine is overloaded.

No it will only rev to 2800 rpm out of gear, and up to only 1600rpm in gear.

When i purchased the boat last year the rev counter didn't work, so i had know
idea how fast it was revving but if did sound allot faster than it does now and
with no black smoke.

Obviously the rev counter is working now, so basically its sounding like the
exhaust elbow or the flexible hose.

 

[nigelmercier]

My volvo penta md6A engine will not rev past 1600rpm there also appears to be a film of oil coming from the exhaust onto the water and black soot on the transom, the engine oil level doesn't change.
All filters have been changed, the prop and underneath is clear of marine growth, I believe that this engine should rev up to 3000rpm.
Does anybody have any ideas to this problem.

I had the exact same symptoms last week (except it was 2000 RPM), and I was rather pleased that my diagnosis was correct: a polythene bag wrapped round the propeller.

 

[Tranona]

No it will only rev to 2800 rpm out of gear, and up to only 1600rpm in gear.

When i purchased the boat last year the rev counter didn't work, so i had know
idea how fast it was revving but if did sound allot faster than it does now and
with no black smoke.

Obviously the rev counter is working now, so basically its sounding like the
exhaust elbow or the flexible hose.

While the exhaust probably does need looking at, that reduction in revs suggests more likely to be prop related. Blocked exhausts etc also tend to lead to poor starting - failure to rev in gear almost always means something is loading the engine too much - fouled prop or incorrect prop are favourites.

 

[cptpugwash]

I had the exact same symptoms last week (except it was 2000 RPM), and I was rather pleased that my diagnosis was correct: a polythene bag wrapped round the propeller.

Thanks Nigel,
I wish my problem was that simple, I checked my prop last week and it was clear of polythene bags and the dreaded barnacles: Have a good and safe sail to the canary Islands, I'm hoping to sail to the Isle of man later this month.
Paul.

 

[Grumpybear]

look at the exhaust elbow next. happened to my 2030.

 

[cptpugwash]

While the exhaust probably does need looking at, that reduction in revs suggests more likely to be prop related. Blocked exhausts etc also tend to lead to poor starting - failure to rev in gear almost always means something is loading the engine too much - fouled prop or incorrect prop are favourites.

Thanks for your help and advice,
I can actually turn the coupling on the prop shaft with my finger with no effort at all.
I checked the prop last week for fouling and was found to be clear, I'm relatively new to this game, I will make some enquires regarding what size the prop should be for this kind of boat.
Paul.

 

[Tranona]

If you have the required data you can get a ball park sizing from using the Propcalc programme on www.castlemarine.co.uk

 

[cptpugwash]

Thanks for that Grumpybear,
The exhaust elbow seems to be the most favourable option at this moment in time, the elbow that is fitted to the engine is the original cast one and has had loads of welding done to it, I might invest in one of those stainless steel jobs.
Paul.

 

[cptpugwash]

I will have a look, thanks again.

 

[nigelmercier]

The exhaust elbow seems to be the most favourable option at this moment in time ...

Hi Paul, I'm sure we would all be interested to know the outcome of this.

 

[Icarus39]

Sounds like your prop is too big ...