New Engine Oil Specifications:
Several years have passed since the American Petroleum Institute (API) has issued new specs, the "Old Spec" being API Service "SN", and "ILSAC GF-5"
Newest API designation is API Service "SP", and "ILSAC GF-6A".
The "SP" designation supercedes all former API oil specifications, and is suitable for all gasoline engines.
"Improvements" = :
1. - Formulated for longer drain intrevals.
2. - Reduced friction affords excellent protection against engine wear and improves fuel economy.
3. - Formulated to reduce likelihood of Low-Speed Pre-Ignition.
4. - Fights volatility burn-off to minimize engine deposits and exhaust emissions.
Look for the API designation "SP" on your next oil purchase to be sure you have the latest engine oil specs available for your gasoline-powered vehicle, regardless of age and/or use.
Early models of Grand Marquis specified 5 W 30 oil, which was changed to 5 W 20 oil for the later year models.
The 95 MERC @ 172,000 miles, runs Pennzoil Ultra Platinum, 5-W-20 Full Synthetic; Bosch Premium Oil Filter # 3410; and a FILTERMAG #SS36PR Magnet Kit. Oil and Filter changes at 5,000 miles.
I used Motorcraft # FL-820S Oil Filters for several years, but changed to the Bosch Premium # 3410 after finding that my oil stayed clean longer with the Bosch Premium filter.

'95 MERC Engine Bay

Sleeping Beauty, Rolling Thunder