5.7 murcruicer oil usage

by Jarrod
(Grandbay al us)

Iv got a 1988 wellcraft aruba 25' with a 5.7 murcruicer. I took it out and it fired up with about 25psi oil pressure drove about 10 minutes it wouldn't plain out real well but did finally get it there.so i looked down at oil pressure gauge it showed 0 psi so i shut it down checked oil level nothing.i put 3 and a haf quarts to full mark.drove about 10 minutes it was busting up wouldn't get on plain so i rechecked oil had to add another 2 to 3 quarts and got under way again same results pulled plugs they where sludged with putty like oil so changed plugs and wires and topped off oil and it ran like a dream for about 15 20 minutes then busting up again plugs are being fould out by oil and there is no smoke well i seen very light blue smoke briefly but thats it no oil appeared to be in water at a stop with engine running no oil in engine compartment or in bilge what can be causing this oil consumption problem i mean 3 quarts every 10 to 20-25 minutes plus oil fouling my plugs but no smoke and no leaks?