Since new, I used MC semi Syn 5-20w for first 40k miles with 5k OCI. Truck never burned oil. Switched to PU 5-20w and truck started to burn oil. It burns about 1qt. every 3500 miles. I am now on my third OCI with PU and it still is burning oil. It’s not a big deal, but I’d like to hear you thoughts on why this might be happening and what I should do. I have a stash of PU still to use up but I guess I could go back to MC. Truck now has 61k miles on it.