Blow By ( combustion pressure leaking past the rings ) is what causes the oil to turn black, on a new vehicle or rebuilt engine the problem can come from the piston rings not being broken in ( sealed ), on a older engine the piston rings wear out do to age, dirty oil, milage, improper lubrication etc, or get weak do to the engine getting to hot and the the rings loosing there tension against the cylinder walls .
On our 1999 Rav4 with 148000 miles the 5W50 Castrol syntec oil and Fram filter are changed every 3000 miles and the oil comes out a dark amber. On our 1984 Dodge Daytona Turbo Z with 52000 miles the Mobil 1 5W50 and Fram filter are changed every 2000 miles and the oil comes out a dark amber. On our 1975 Dodge 1 Ton Club Cab Duely truck the Pennziol 10W30 break in oil has not been changed yet, the new motor only has 900 miles on it. The oil is nearly black already and will be changed before this hunting season. the oil will be changed to 5W50 Pennzoil synthetic and the oil and Fram filter will be changed every 1000 miles . ( I like to spread my wealth around ) :wink: :wink: .
Paladin......Have Rav , Will Travel ! :cheers: