Halderman: Yes, Shell Rottella T for diesel engines would be the right oil to use. You could also use Mobil Delvac oil because currently these oils contain enough zinc to prevent damage to the flat bottom valve lifters and camshafts. I think either SAE 10W-30 or SAE 15W-40 would work as long as you are not starting in very cold weather. I would NOT recommend the use of the synthetic version unless the engine has been overhauled and seals have been updated to the latest materials. Older seals and gaskets are not compatible with the old rubber and gasket material used before about 1980.
Instead of using diesel oil, you could also use conventional oil and add a zinc additive. Actually, this might be the best for you because you can select your favorite brand of oil and be assured that the there is enough zinc to protect the engine. Emissions standards are getting tougher almost every year and the oil companies have to formulate the oil to reduce chemicals that could affect the catalytic converter. Even diesel engines today are equipped with catalytic converters and that is why we are seeing a reduction of zinc levels in diesel oils.
James D. Halderman is an ASE-certified master technician, a member of the Society of Automotive Engineers and the author of 12 textbooks. Submit your questions to Halderman via e-mail at jim@jameshalderman.com or follow him on Twitter @jameshalderman, or write him in care of: Wheels, Marketing Publications Department, Dayton Daily News, 1611 S. Main St., Dayton OH 45409.
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