Looking for opinions and or professional recommendations for oil viscosity for a 1986 GT 5.0 with 85k miles. Rock on and many thanks in advance.
Zero mods - I'm in Southern California and for the past three weeks its been slightly over a 100 dees grees - average year around temp here I would say in the mid 70's 80'sAny mods and where do you live? Location can have an impact on viscosity. I run 10W-40 as it gets pretty hot in Oklahoma and the car never sees the road from about mid-November through mid-March.
I've been runing that Rotella 15-40 diesel oil, this time and last time. I gues on the next go around iI'll go with 10-40 but what brand would you consider.I would go with what Bullitt347 suggested then. If you have good oil pressure then no reason to do anything else. If you have cats then stay away from lubricants with zinc, phosphorus, and sulfur as they have been shown to kill converters.
I've been runing that Rotella 15-40 diesel oil, this time and last time.
Do NOT run diesel oil in a gasoline engine.I've been runing that Rotella 15-40 diesel oil, this time and last time. I gues on the next go around iI'll go with 10-40 but what brand would you consider.

Simply pull out the owners manual and follow the manufacturers directions.
Don't overthink it.![]()
Thank you, thats exactly what my inner voice just said to me -Owners manual 40+ years old and lubrication technology has advanced in 40+ years by quite a bit. I don't think it it is over thinking rather more like understanding what is available today that is better than the offerings 40+ years ago.
I'm sure you're correct but exactly why is that -Do NOT run diesel oil in a gasoline engine.
Well first it contains additives that are bad for cats, zinc I believe is one that is bad for cats so if your running diesel engine oil and no cats you're ok. If you have cats stop using that oil, it takes a lot of miles, like many oil changes before cats show effects.I'm sure you're correct but exactly why is that -