Here's what Mobil 1 says about it:"Myth:
Mobil 1 can't be used in diesel engines.
Reality:
Mobil 1 will provide excellent service for passenger car and light duty truck diesel engines (API CF or CD), as well as European diesel cars that require oils to meet specific car builder approvals or ACEA-quality oils. (This is the oil specification used in Europe and developed by European car companies.) Additionally, Mobil 1 Truck & SUV Formula is designed specifically for light-duty diesels that require an API CI-4 oil. Be sure to check the oil quality recommended in your owners' manual for your diesel engine.
Heavy duty truck engines that require API CE, CF-4, CG-4, CH-4 or CI-4 should use one of the products from the Delvac? line ? Mobil Delvac 1? synthetic engine oil or Mobil Delvac 1300 Super?. Mobil Delvac 1 synthetic oil can help improve fuel economy, extend oil drain intervals, extend engine life, provide enhanced wear/cleanliness protection and reduce oil consumption."
http://www.imperialoil.ca/Canada-English/Products/Lubricants/PS_L_Synthetic_myths.asp
I would stay with the same weight of oil that is specified in your owner's manual.
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'70 Mustang Mach 1 - '70 Mustang Convertible - '72 Mustang Sprint - '94 F-150 XL