12 hp diesel- black soot and low refs

[killick]

The 12 hp Westerbeke diesel engine in my boat ref well with virtually no smoke or soot when out of gear.
In gear the refs stay at no more than 2000 rpm and there is black soot in the cooling water.If the barnacles are removed from the propeller the refs increase to 2500 rpm but nowhere as high as it used to be. This problem has been developing over quite some time.
Any advice will be greatly appreciated.

 

[Billjratt]

Partially blocked exhaust probably.

 

[Avocet]

Does it have an air filter, and might that be blocked? Try temporarily running it without the air filter to check.

 

[vyv_cox]

Yes, as Billjratt suggests, exhaust manifold is probably the first place to look. Air filters rarely block on a boat as there is mostly no airborne dust but something may have moved in there.

 

[ianj99]

The 12 hp Westerbeke diesel engine in my boat ref well with virtually no smoke or soot when out of gear.
In gear the refs stay at no more than 2000 rpm and there is black soot in the cooling water.If the barnacles are removed from the propeller the refs increase to 2500 rpm but nowhere as high as it used to be. This problem has been developing over quite some time.
Any advice will be greatly appreciated.

Is the hull clean? Doesn't take much fouling to cause enough drag to increase the load on the engine and hence reduce the revs, especially when the engine is just big enough for the boat.

 

[Stork_III]

Partially blocked exhaust probably.

I would say definitely almost total blockage.

 

[PetiteFleur]

Definitely partially blocked exhaust elbow - to see it properly, you'll have to remove it and inspect on the bench - just looking up it won't work!
When this happened on my previous boat I had to fit a new elbow - it was like having a new engine when tested!

 

[killick]

Thank you. How is the elbow secured and how do you remove it?

 

[Tranona]

Almost certainly 3 or 4 bolts. Need to remove the exhaust pipe and probably water injection pipe first. I'll probably be a struggle to break the gasket seal. Make sure you use a new gasket.

 

[GrahamM376]

When did you last have the injectors serviced?

 

[corinthmistral]

Is the hull clean? Doesn't take much fouling to cause enough drag to increase the load on the engine and hence reduce the revs, especially when the engine is just big enough for the boat.

+1. Start simple. As you say the prop was fouled and has been cleaned, if you haven't cleaned the hull it will make a noticeable difference on this size of engine if fouled. Fouled hull makes a noticeable difference on my 28hp volvo.