D6D uses 2 quarts per hour

15w40 is pretty standard oil for the D6D. i don't think 40 weight will help much. one thing though--- change the inner and outer air filter. you could be sucking oil around the turbo bearing seals. does the engine have blow by???

Gees! sounds like the pistons dont even have rings on them!

Sounds like a rebuild will work out cheaper than the volume of oil you need pretty quickly.

do you have a link or links to previous posts that may enlighten us to what work you may have done to this engine/machine in the past or recently to get it going again so then we can decide on a cause or some other problem and place to look for a help solution ?
You know your machine better than we do and its history as we deal with many machines and problems most days on here and so have trouble recalling your particular case.
Regards,
Eddie B.

Do you know the hours on that 3306? The reply from bursitis about the air filters is a good start. I know an overhaul is expensive but please bear in mind that high hour 3306 engines are known to break valve springs. A local independent repair shop had a D6H in this year that had a catastrophic engine failure due to a high hour valve spring failure...the block, crankshaft and cylinder head were all damaged beyond repair!
All valve springs should be replaced at overhaul time.
Craig