15-50 and engine smoothness....

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May 28, 2002
Ever since I put in 15-50, my engine runs smoother and quieter...idles better with less disturbance when the a/c cycles and there's less driveline shutter and smoother take-offs... Do you guys think that European manufacturer's (and those outside the U.S.) recommend thicker grades due to engine running quietness and smoothness as well as necessary protection at 250kph (150 mph)?
I think they specify the higher vis because of hotter engines, looser clearances, and higher running speeds on the open highways.
I don't think the clearances are looser, maybe the oil passages are wider? Ring design different? Engines higher revving?
Originally posted by MolaKule: I think they specify the higher vis because of hotter engines, looser clearances, and higher running speeds on the open highways.
I agree, I have always heard they ran thicker oils due to higher cruising speeds down highways.
"Looser clearances in European cars? Please explain." What I mean is that the diametral clearances of the bearings are larger, the ring tensions are lower. and ring gaps are wider. I also read a paper which stated the European engineers were gearing up to run hotter engines than ever before. If that is the case, then higher viscosities are needed. In the Interesting Articles thread, "Bearings and Filtration" I explain the relationship between oil viscosity and bearing temperatures.
Molakule: Thanks for the reply. I think your answer raises a few questions. My 2001 Toyota Echo has exactly the same engine, compression, horsepower and torque specifications as the Yaris 1.5 which is basically the same car sold in Europe. The only difference is that in Europe they specify using higher octane gasoline, not because the car would not run on 87 octane but because this type of gasoline is not available anymore. The 1.5 liter Toyota engine has knock sensors like any modern engine and the computer just changes timing a little to compensate for lower grade gasoline. I have tested using 91 octane gasoline on this car and it definitely gets better mileage (about 3%) but it is not enough to justify the additional cost.
Thought I'd share this reply I received today from Mobil what the differences are between N.A. and Europe: "Europe has much different ratings, they are more concerned about fuel economy. Oil companies do not decide what grades of motor oil to make that is determined by the American Petroleum Instituite and auto manufacturer's. What auto manufacturer's call for in their owner's manual's has a lot to do with what oil manufacturer brings out on the market. The Mobil1 15W50 has no problem flowing and lubricating your engine in cold temperatures. Mobil1 15W50 can flow at -49 degresesF." Europe more concerned about fuel economy? Wonder who answers these questions for them....
Dr.T, the engine is percieved to be smoother because of two main reasons, The synthetic 15w-50 M1 has less resistance to flow because it is synthetic and most importantly it is dense enough to quiet the engine noise. A thicker oil will dampen sound resulting in a percieved better running engine. My opinion.
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