Augustus

The OP isn't trying to scam the dealer out of a free oil change. The issue is that the OP believes his Z is having oil consumption issues, and this particular dealer insists that they must charge him for a full oil change to begin the in-warranty process of confirming or denying that the problem exists.

If a full oil change is required by Nissan for the test (which as others have said, it isn't), then the dealership should have recourse from Nissan for the oil change cost, not the customer. If the full oil change isn't required, then it's just the dealer's service department being ignorant or willfully spiteful.

IMHO, the solution is for the dealer to charge you for the oil change but agree to refund the money if there's a problem. Or do it for free but with the agreement that the OP pays them if no problem is found. The dealership has a right to cover their margins, but the OP also has a right to warranty coverage not predicated upon paying for unnecessary services.

I hate to say it, but this is an example of where you can run into problems by doing your own service / oil changes. No, a dealership can't deny you a warranty claim. And I absolutely agree that it's cheaper & more satisfying to do your own oil changes. But a dealership has the right to question your methods if you do your own service and problems arise. I have to think that had the OP been taking the Z to this dealer for regular service, then they wouldn't have given him any crap about needing another oil change. A), they would have done the change, and B) you'd have an established & ongoing relationship with the service department.