Texases; here is the response I posted to another question about a vehicle which began consuming oil after switching oil types, which contains the specifics about my client (and friend's) 1982 Toyota Cressida's engine destruction in 1997.
If you changed to a different brand; this may have caused the problem (depending on what the two brands were). Some oil companies claim their oil is compatible with any other oils; and some people on this site buy that sugary, oversimplified PR. But there are many people who have experienced very much the opposite: I am one of those people. I once bought a Dodge V-8 which was in very good condition, and had previously been run on only Shell oil. Shell oil is unique in that they use alkaline additives in it; with the intention of counteracting acid formation created by cold running. I know of no other oil manufacturer which uses alkaline additives in their oil. Since I go to great lengths to not start my engine without driving it far enough to fully warm up and boil off the condensed moisture; the idea of alkaline additives has no value to me. So I promptly switched the car to Union 76 oil; which was my regular oil at that time. And during the next 60 days; the engine rapidly lost compression and power, and soon degraded to the point where I had to have the piston rings replaced. The engine showed no signs of a compression problem before I changed oil brands; and I did not abuse or mistreat it at all.
A very similar experience happened to a good friend, who is a physician; and who had been using Castrol Syntec full synthetic oil for years in his Toyota Cressida with great success. For some reason, he decided that it was extravagant to pay the cost of synthetic oil (on a doctor's income); so he switched back to Castrol GTX regular oil. And the Cressida soon began consuming massive quantities of oil; and putting so much blue smoke out the tailpipe that my friend said he could not drive it anymore in good conscience. That was the end of his Cressida.
I have a now out of print book on engine tuning for performance; which stated that many professional engine builders will go to great lengths to NEVER allow a different oil brand to be put into their engine. This is the result of repeated experience in which engines were ruined from the chemical reaction between different oil formulations. Sometimes adding even less than a quart of a different oil brand has been enough to ruin a perfectly good motor.
In over 40 years of tuning cars for a living; I repeatedly found that some people's cars lasted longer, and consistently ran better than other supposedly identical cars of the same make and model. So I began collecting information about fuel and oil usage in my client's cars. And I soon found out that those cars which ran so much better than average were inevitably the ones which always used the same brand of oil. It didn't seem to matter so much which brand it was; the main thing was that the oil was always changed at the same gas station (this was before the days of quick oil change places). And this, by default, meant that the same brand of oil was always used; since each gas station in those days only carried their own brand of oil.
If you changed oil brands at that last oil change, I believe this was the cause of the increased oil consumption you now experience. There are things you can do to undo some of the chemical consequences that brought about your oil consumption. But there are so many doubters and know it alls on this site who prefer myths and slick marketing hype over my direct experience (and that of successful tuners and racers); and they will probably try to convince you that I don't know as much as they do, so I won't waste my or your time by saying anything more about this unless you ask me to. Please refer to my response to your other post on the value of switching to synthetic oil.