Hi guys.... I'm the proud owner of 98 Deville and I've always used Mobil1 High Mileage 10w-30....my mechanic said if I used Mobil1 15-50 that it would help with the oil leak that all northstars seem to have.... any input on that notion????
Aside from the leak sealing guesswork, the oil use advice is mostly fact, not opinion. 15W-40 and 15W-50 oils are reserved for some really heavy duty commercial engines as well as air-cooled motorcycle engines. The research ship that I captained for 12 years had four twin turbo Cummins V-12 diesels, 720 hp each. Those engines used Drydene 15W-40 oil and had a 3,000 hour overhaul interval. 15 gallon sumps.Well after considering ur opinions.... I stayed with my gm recommended 10-30...thanks guys... y'all r awesome
Bearing clearance is the key. You can run thicker oil in old engines with big clearances but not in a Northstar with tight clearances. Very bad advice from the very old school mechanic.My MGB's used the heavest weight of any of my other cars at 20W-50. The MG's engine was built with big clearences.
I also used to use Aeroshell 100 (50 weight) in my 1951 M38 Jeep but that was because it would sit for extended periods of time and the Aeroshell would stay in the bearings and oil pump better than anything i found. (kept the dry starts at bay) But i was verry carefull how i ran it and never loaded it cold. The Willys also had big clearences. I would not recomend this to anyone else.