Quote:
Originally Posted by flatheadmurre
Today some of the manufacturers state their GL-5 to be redmetal safe to.
In the specification it often says API GL-4/5 meaning it has what it takes to fill the specification of GL-5 but should be safe to use in a GL-4 aplication.
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I have read many articles that question this. They find the GL-4/5 rating to be inconsistent and misleading. I would not trust it myself, as long as GL-4 is available why take a chance?
Here are some examples of the confusion.