Motor Oil

[Mark Rahn]

Tech Tip by Chris Trautman
chris.trautman@corvette-web-central.com
The myths on motor oils:
Has Zinc been removed from Motor Oils? Some people have seen problems of engines failing and the consensus seems to be the removal of zinc from the motor oils. Is this a true claim and do you think a zinc additive might help?
Answer:
The EPA ordered the removal of the zinc from over-the-counter motor oil.
The active ingredient that we are talking about is phosphorus which is added through a component called ZDDP. For products that meet the new Oil ILSAC
GF-4 specification the phosphorus levels for the oil must be less than 800 ppm phosphorus. The ILSAC level for phosphorus has been reduced to protect the catalytic converter and other emission protection equipment. The engine manufacturers are confident that this level of phosphorus will protect both new and older engines. However, they have nothing to lose and everything to gain. There are oil products which have a higher level of phosphorus (phos) and can be used in engines in racing or high performance applications. The engine component that needs this the most is flat tappet lifter style camshafts that are found in older cars and Corvettes. The zinc helps cushion the impact of the operation with this type of valve train. This view is still a hotly discussed and disputed topic. From a troubleshooting standpoint you always go back to what you changed last as a source of the problem. The problem here would be the change of the oil chemistry. Until proven otherwise we believe this to be the smoking gun.
The C5 and C6 Corvettes have roller lifter and rocker arrangement. This type of design reduces the friction which is great for horsepower and also increases longevity of engine parts and oil break down! Thus this problem would not be an issue on the newer fleet of cars being produced in the last 15 years. These generations of cars need to continue using what the manufacture recommends.
For reference all 53-86 Corvettes use flat tappet style lifters. To make a long story short never use any newer type of regular or synthetic motor oil with a ILSAC rating on the label of GF-4. For these cars we recommend 10W-30 reading the label and suggest looking at Shell Rotella “T” or Chevrons “Delo 400” both of which state “phos” of over 1100ppm. Names change so always read the labels and don’t put anything in your pre 53-86 Corvette that does not have at least a phosphorus “phos” of 1100. Research the labels, know what “phos” the oil is and extend the life of your engine!

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