White smoke with engine
under load is typically caused by not enough fuel
compared to the amount of air available for combustion. Too much fuel (compared to air available in combustion chamber) will cause black smoke (not complete combustion of all fuel in that case). In your case the engine while reving up along side the key (zero speed) will be higher loaded then while steaming at same RPM
(propellor formula). Hence at keyside your engine is pumping in more fuel to reach the same RPM
as compared to while underway. If the engine is not super charged (turbo) the ammount of air has remained the same for the same RPM as while underway, hence the fuel / air ratio has changed in the sense there is now more fuel available alongside the key then while underway, causing complete combustion which is colorless.
You mentioned a reduction of power, this supports the above.
Typically this is caused by reduced volumetric efficiency of fuel pump
(high pressure pump). This happens over time and is normal wear and tear.
A failing injector typically will inject more then required fuel in the cylinder (worn out injector spring or worn injector holes) which will cause incomplete combustion, which will become evident in black smoke from the exhaust
The much cooling
water (e.g. failing theremostat) again will typically result in not complete combustion (temperature not high enough in cylinder under load), evident in black smoke from the exhaust. Not enough cooling
water will typically not result in a change in exhaust gas color, as the combustion is only improved with higher temperatures. Your engine material and engine structural limitations however require a limit to exhaust gas combustion chamber temperature, hence the thermostat requirement. Any issue with cooling water you should observe in your cooling water temperature (should be between 80 and 90C)
Your best bet is your high pressure fuel pump
. There is not much you can do yourself typically. Pump pressure would be required to be measured to verify if these are still within the required range. Overhaul
of bore and plunjers and valves will be required if worn out.
Best Peter A S