Steve, smoke color in a diesel usually has different causes than a gas engine. White smoke on a gasser generally = coolant getting into the combustion chamber whereas it is usually a totally different problem in a diesel.
Generally, white smoke in a diesel = unburnt fuel in a cold engine, i.e. incomplete combustion.
Most common causes are:
1) One or more glowplugs aren't working which causes incomplete combustion in a cold engine.
2) You could have one or more injectors that are not atomizing correctly, i.e dribbling excess fuel, also a cause of incomplete combustion.
3) Injector pump is not timed correctly. I wouldn't suspect this unless you've had it off and/or have tried to adjust it.
It could also be as simple as bad/contaminated fuel.
Once the engine warms up to it's normal operating temperature it'll burn the excess fuel more completely so thats why you may not notice it once it's warmed up. Course seeing black smoke on a warmed up diesel can have the same cause as the cold engine w/white smoke.
Check your glowplugs and make sure they are all working.
Since you are now noticing the engine performance suffering some, you may want to pull the injectors and have them bench tested, that may bne a good winter time project
Let us know
2004 Kubota BX23 w/60" MMM, Thumb, AM/FM/CD.
1966 Wheel Horse 856, Gear.
1966 Wheel Horse 876, HST.
w/50" sicklebar mower, 36" rotary mower, snow blade, alternator/welder.
The USMC, providing the enemies of the USA the opportunity to die for their country since 1775.