Engine workout, “Italian tuning”.

Sailboats engines are many times “over-sized” as boat owners wants to have reserves when motoring in high winds and when maneuvering.

The side effect of over-powering, is that we only use 50 – 60 % of the available power to make cruising speed in normal conditions. This means we will be running the engine on light load most of the time.

Diesel engines are not made for running on light load, and will suffer from carbon build, due to low combusting temperature.  Carbon deposits is a result of incomplete combusting of diesel fuel.

If you have a modern “marine engine” with computer controlled fuel injection, carbon deposits will be less of a problem, as the amount of fuel injected will be ideal compared to the real load. At least one advantage for the new technology!

All engines has a recommended max RPM.  It is important that the propeller is dimensioned to reach the recommended RPM.  The proper size of the propeller is a factor of engine HP, reduction ratio on gearbox, water line, propeller diameter, number of blades and pitch. There are softwares that can calculate the size of propeller and get you close, but as always personal experience is important to get it right.

If you are considering a new propeller, make sure the supplier accept to change it, in case the calculations and experience did not take you close to the expected RPM. (Check the technical specification what the recommended RPM is.)

It is important that you know what the maximum RPM is with WOT (wide open throttle). If you do not know, go out and check with a clean bottom, clean propeller in smooth water.  Write up the numbers in your boat manual, and do this test on a regularly basis.  It is a good indicator how your engine is doing, growth on bottom or propeller.   

If you would have any engine problems in the future this is one of the test you can do yourself, before contacting the workshop.  Your mechanical shop will ask for the number.

As long distance cruising means a lot of motoring, we tend to use a much lower RPM than what engine manufacturer recommends.  On Bella Luna we normally cruise at 2000-2200 RPM (Maximum RPM is 3200),  in order to get a better fuel economy and better comfort in general.  If we run the engine on 2000 RPM for extended periods we get carbon building up in the combusting chamber, on valve seats, injectors, turbo and exhaust system.

To burn the carbon deposits it is important to exercise your engine regularly.  If not your engine will get carbon deposits that will damage the engine.  I  got following advice from the technical manager at Yanmar, Sweden.

Run the engine at  2900-3000 RPM for minimum 20 minutes after every 4-5 hour on light load.  (Maximum RPM for our engine is 3200) He explained it takes about 10-15 minutes for the combusting temperature to reach 560 °C. Carbon deposits will not burn at lower temperatures.   

 It is important to understand that you are trying to burn deposits,  and not trying to blow the sot out by running on high RPM.  The sot that you see coming out  when rewing up, is just the tip of the iceberg.

This high RPM running is sometimes called “Italian tuning” and perfumed also by respected diesel mechanics.   If you already have carbon deposits, I recommend you try this before visiting a repair shop.  It might take several runs before you see an improvement. There is a big chance, that the engine performance will improve and you do not have to visit the workshop.

Turbo engines suffer more, as the turbo is driven by the exhaust and is a part of the exhaust system.

Non-turbo engines are less sensitive but not immune.

I think it is unrealistic to think that cruisers will change behavior, and start to use the engine on the high load as recommended by the engine manufacturer.  Fuel consumption and engine noise will not be acceptable.

An acceptable compromise is to run on light load, and give the engine a workout every 4-5 hour.

Just to give you an idea:

On Bella Luna we burn about 0.6 l/Nm at light load. (2000 RPM)

If we would run at 2700 to make the engine perfectly happy, we would burn twice the amount and gain only one knot boat speed.




7 thoughts on “Engine workout, “Italian tuning”.

  1. Johan Virgin

    Hi Roland,
    It is normally difficult to reach max rpm with the prop rotating. When running at high rpm do they mean that it is possible to reach appropriate temperature without loading the engine with a rotating prop?
    I think you are touching a common situation, hundreds or thousands of hours at a for the engine too low rpm.
    Johan Virgin
    HR43 Therica

    1. Roland Post author

      Hi Johan,
      I´m not sure what you mean with max rpm?

      The max rpm I´m referring to is the RPM you get with the gearbox, in forward gear and full throttle.

      This will be your max RPM. If you do not reach the RPM that the engine manufacturer recommends, it might be
      a problem with one of the following:

      -Engine, Turbo, fuel supply
      -Overpropped (To much pitch on the propeller)
      -Barnacles on propeller and or hull

      You can only do the “Italian tuning” when the boat is in gear. You will not reach the right engine temprature in light load.

      If you have a Gori propeller with overdrive the “Italian tuning” should be done when the propeller
      is in normal gear (pitch)

  2. Trond Andresen

    Hi Roland
    I hope a lot of boat owners read your story about Italian tuning. It might possibly save them a lot of trouble and money. I have previously shared my experience with carbon deposits on the HR user forum. In my case, the deposit of carbon in my VP D2, 75hp, totally jeopardized the turbo charger and I had to remove the engine from the boat and split the block to examine the cylindres for possible negative consequences – in addition to the replacement of the charger. A very expensive affair, indeed! The ironic issue is that I had the boat delivered with the genious and highly recommended Gori prop in order to be able to run the engine at lower rpm for improved fuel economy! A pretty lethal combination! And the sad part is that the VP instruction manual tells you nothing about the need for Italian tuning.
    Trond/HR 43 Lady M

    1. Roland Post author

      Hi Trond,

      Thanks for the comment. Sorry to hear about your problems. I doubt that you find the “Italian tuning” advice in any engine manual.
      You will however find it in some “Diesel mechanics books”

      In the HR manual you find a warning for running the engine on low RPM and not using higher RPM occasionally.

      The problem is running the engine on low load, independent of make of propeller.


  3. Jeff Bander


    Great article. Exhaust system on my boat became severely restricted due to carbon buildup which restricted RPM and boat speed under power. Who knows what was simultaneously happening inside the engine. All I know is that with fix to exhaust lost power was regained.

    I have read about crank case filters which filters out particulates before sending air back to air intake. The implication is that this makes for a healthier engine, especially a turbo charged one, as this helps a oid carbon buildup on the turbo blades. Any feedback on this?


    1. Roland Post author

      Thanks Jeff,

      I have no experience from crank case filters. I guees a filter would filter out some of the oil mist in the crankcase. But I do not think oil would cause any harm. I have used 2-stroke oil in the fuel ever since the injection pump stopped working after 400 hours. Today we are over 1000 hours and there are not any signs of carbon deposits on turbo or injectors. There is a very thin sot layer on the turbo blades. But not more than you can expect. Yanmar recommend turbo cleaning on a regular basis. Have done it once but did not really see a significant difference.

      Carbon deposits after the turbo causes more back pressure. Higher back preassure can result in more carbon build up in crankcase, valves, piston rings.


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