Yeah, the old "break it in on dino to seat rings,bearings,etc" is an old wives tale. Many new and very expensive vehicles come from the builders with synthetic oil
I did not say it could not be done. Here we're dealing with an engine owner who says his new replacement engine is burning oil like his original engine did from day one. Both of these engines came from the factory with dino oil, NOT synthetic. Synthetic from the factory on high end engines or run of the mill new trucks is the manufacturer's choice. Some do, some don't. The question is about mixing oils on the second engine that seems to be having oil related consumption issues. It has dino oil. Adding syn to the dino isn't likely to change anything, in fact it might improve, i.e. reduce oil consumption over time, but that's another discussion.
I don't recall where I read it, but the thinking was if an engine had dino oil in it from the factory to wait until after the first oil change to switch to synthetic. That can't be a bad thing, and where one chooses to add synthetic to a brand new engine before the first oil and filter change is due is probably not earthshattering either, in the long run.
Amsoil, as but one example, does state in their FAQ section that mixing syn with dino does reduce the extended interval oil change otherwise used when using ONLY synthetic.
Note that the OP has not described what he means in any quantitative way, by burning oil in either engine's case.
That info would be helpful in determining what it is he is really dealing with regarding these two engines. I doubt the manufacturer would agree to swap out engines without a serious issue behind that choice. More info from the OP would be useful....
And several years ago a few synthetic oils were and still are today blends, as others have mentioned. So the final answer as to what works best for all situations/engines is, IMHO, still out.
