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TechManSteve, ASE Certified Master Technician
Category: Ford
Satisfied Customers: 147
Experience:  My automotive and engineering experience is based on Fords. I cut my teeth on a 1970 LTD
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That put 10-40 regular car motor oil in a diesel engine not 15-40 what

Customer Question

I know someone that put 10-40 regular car motor oil in a diesel engine not 15-40 what will happen to the engine?
Submitted: 10 years ago.
Category: Ford
Expert:  TechManSteve replied 10 years ago.
Diesel specialized motor oil is basically identical to products for gasoline engine except that they have more additives that keep soot particles in suspension... a condition not present in a properly running gasoline engine. A significant number of "regular" motor oils qualify for use in many diesel engines. For both - you need to read the read the appropriate spec on the oil in question "S*" for spark ignited and "C*" for compession ignited (Diesel) engines to know that the oil meets or exceeds what was originally required. Example: An engine needing "SF" oil can use SF, or the newer SJ. Similar with diesel specs.

Except for 2006 and later VW TDI engines requiring a very new specification, most diesel engines will be very tolerant of using regular oils.

Your reference to 10w-40 vs 15w-40 is a VERY minor difference in viscosity and has no bearing on the oil's usability in a diesel engine if it has the letter spec equal or higher than required for that engine.