But you won’t be generating enough work and heat at 1600rpm you’ll be glazing bores and coking the turbo unless you regularly run it up to at least 75-80% power. So yes you might find 1600rpm is a lovely ‘pottering’ speed but you need to run up to mid 2000s frequently to get the turbo spinning and hot. If you try gradually increasing rpm you’ll start hearing the turbo coming ‘on song’ around 2200rpm and really getting into its stride at 2400+. You need to run it at these speeds for a good burst every few outings. Your max is 3200rpm and every few weeks you should run it up to close to that for at least 5 mins.
I've attached details of the Turbo cleaning instructions shown in the Yanmar Service Manual in case anyone wants to do it at some point. Just click on the thumbnail to get more detail. Seems simple enough as long as the warning in 5 is strictly observed.
Instructions: When engine speed seems sluggish or the exhaust color poor, the blades of the turbocharger blower may be dirty. Wash the blower using the following procedure: 1. Prepare blower wash (liquid detergent), freshwater and a small pitcher. Blower wash (4L) Parts code: 974500-00400
2. Put the clutch in neutral and run the engine at high speed, 2500-3000 minimum (rpm).
3. Slowly pour approximately 50cc (1.7 oz) of blower wash into the inlet hole of the intake silencer over a period of about 10 seconds.
4. After about 3 minutes, pour in approximately 50cc (1.7 oz) of freshwater in the same manner over a period of about 10 seconds.
5. After operating the engine for about 10 minutes, check the boost pressure and power output. If there is no improvement after washing the blower, repeat the washing process several times. NOTICE: Do not pour in a large amount of blower wash at one time. This can damage the blower blades and cause water hammer in the combustion chamber and cause damage.