2000 Ford Mustang V6, 77,000 miles.
Car is using oil, .5 quart every week.
What is best oil to use, and should I put an additive in?
Have you had any gaskets replaced? If they're the original gaskets, it's almost 24 years old now. Anything rubber starts dry rotting after so long, especially if it's only been driven 77,000 miles in 23 years. Your rear main could seeping as well after all these years. Do you notice oil spots when you park? If you do, there's an oil leak. Track it down using UV dye, and some special glasses you can get at AutoZone. Get the kind meant for oil leaks. If it's none of the above, your engine is burning it. Check your PCV valve. It may be stuck open if it's never been changed.
What is best oil to use, and should I put an additive in?
The owners manual states a 2000 Ford Mustang 3.8 liter uses 5W-30 full synthetic oil, so use what the owners manual requires, 5W-30 full synthetic. And no, don't use any additives.
You can download the owners manual here: https://ownersman.com/manuals/2000-Ford-Mustang-owners-manual
