I was told that it's a bad idea to switch from conventional full synthetic oil in high-mileage vehicles. Those are a cause of gas switch taking-ins.
I actually had a discussion with an engineer at Chao and this guy was an expert. I mean, they design all else. He said that synthetic oil can’t do anything like that. But, I had to argue back at him, because I’ve seen it happen so many times. I had to disagree with him.
There’s something in full synthetic oils that they think flow better, which they admit--they flow better. But, if they flow better, they also can flow through sips of little crevices in older engines and also they can flow around the piston rings.
I had a lot of customers with old vehicles, who switched to synthetic and some of them leaked. But, a lot of them burped old oil. That’s just what happens. If you have normal, conventional oil on an old car, just keep using it. The only thing I advise to do if it burns a reasonable amount--go to a heavier weight oil plug, maybe a quart of Lucas oil additive can change the oil and that can help out a little bit. I’m not a fan of changing to synthetic on the old engines either. Even though the engineers told me that was impossible, I know it’s not true because I’ve seen it happen.