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Does Mobil 1 0W-40 Make a Turbo Engine Susceptible to Coking?
 
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Question:
Does Mobil 1 0W-40 Make a Turbo Engine Susceptible to Coking?
With my previous stock engine '01 Miata I used nothing but Mobil 1 0W-40 with completely satisfactory results on the street and track for over four years. I have recently replaced that car with a very low mileage '04 turbo MAZASPEED Miata and am using the same 0W-40 Mobil 1 oil for street and track. However, I have been strongly advised by seemingly knowledgeable MSM forum gurus that use of an oil with such a wide viscosity range in a turbo powered car makes the turbo bearings subject to coking. I routinely see oil temps of 230°-260°F here in the Arizona desert and would appreciate your technical opinion re the coking issue and whether Mobil 1 0W-40 is the appropriate and best oil for my MSM for street and track combination use in very hot southern Arizona.
-- Richard Olsen, Green Valley, AZ
Answer:
We would recommend you use either Mobil 1 5W-30, which has demonstrated outstanding performance in the HONDA HTO-6 Turbo specification and is recommended for Honda RDX Turbo, or Mobil 1 0W-40. Your friends are correct - wide multigrades can sometimes contribute to deposits.  However, in the case of the Mobil 1 formulations, this is not an issue since it is formulated with high Viscosity Index base oils. This means it does not require excessive viscosity modifiers like conventional oils with a wide range viscosities. Secondly, Mobil 1 0W-40 carries all the outstanding qualities of all the other Mobil 1 grades including outstanding turbo performance and high temperature stability.
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