I have a 1989 Mercury Grand Marquis with the 5.0 and AOD, of course. It has
209,000+ miles. While it still runs great and shifts firmly, it does use quite a bit of oil, about a quart every 400-500 miles. I wish it was a leak, but it's not.
Ordinarily you can't see any visible smoke, but when you're accelerating moderately or more you can see a mild to moderate fog behind you.
I've never been a snake oil kind of guy, but I've never had a car with mileage this high. Would something like STP be advisable? Considering that winter is setting in, I don't really like the thoughts of thickening the oil or using a higher viscosity (I still use the recommended 10w30), but perhaps the benefits would outweigh the dangers.
Thanks in advance,
CJB