Hello Niels and all,
At the risk of overkill, I am re-sending a posting I made a few
years ago on the subject of turbos:
Volvo TMD 22 Turbo: Lessons Learned
During the past summer, I learned a lot about the TMD22 Volvo diesel
engine and its turbocharger. Let me share some of that with those
who helped me solve my problems.
My symptoms were:
• Increasing amounts of black exhaust soot on the side of the boat,
to the point where I had to clean it after just a few hours of
• Inability to run the engine over 2100 RPM under load, although it
would run to 4000 RPM in neutral.
I checked all the obvious: no restrictions on the air intake, clean
prop, clean fuel and filters (Racor & engine), good throttle
linkage. Then I had the injectors cleaned, and they had quite a bit
of carbon build-up. But that didn't change anything. So the only
other possible source of the problem was the turbo.
I talked to some other sailors, including two South Africans who
happened to be diesel mechanics – one on a submarine(!), and the
other a Caterpillar engine mechanic. They explained the turbo to me,
and ultimately told me how to remove it, clean it, and re-install it.
The turbo runs all the time, not just at high RPMs, as some have
suggested. Its role is to force more air into the engine than normal
aspiration would provide. It runs by using the exhaust gas to turn a
turbine, which is on the same shaft as a compressor on the intake
end. The turbo also has a wastegate built into the exhaust side, so
that at very high power settings, some of the exhaust gases bypass
the turbine, preventing the compressor from overpowering the engine
Now, since the turbo is in the exhaust flow, it receives all the
carbon that is normally in the exhaust gas of a diesel. That is why
it is a good idea to run the Volvo TMD22 at max RPM once in a while,
to burn off the carbon in the exhaust stream. Otherwise, the carbon
will build up and start clogging the turbine and the wastegate
valve. In extreme cases, the whole turbo will seize up, requiring
replacement or major repair.
In my case, after 1600 hours of motoring around the Med, I had a lot
of carbon build-up, but the turbo still turned. However, the
wastegate was partially clogged open, so that even at low RPMs, some
of the exhaust gases were bypassing the turbine. As a result, the
compressor wasn't running at correct speed, and the engine wasn't
getting enough air. Thus, the black exhaust. Also, at high RPMs,
the boost compensator on the fuel rack wasn't receiving enough
pressure from the compressor to open, so the engine wasn't revving
above 2100 RPMs. Basically, the fuel rack wasn't feeding more fuel
to the engine, even though the throttle called for it.
The solution: Remove the turbo (explained in the shop manual), and
clean the carbon from the exhaust side. Also clean the exhaust pipe
leading to the muffler/mixer. I took the turbo to a specialist shop
in Arrecife, Lanzarote, who cleaned it for 40 Euros. Problem solved.
Any questions, let me know if I can clarify any of this.
Good sailing to all, Roy Benveniste