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Why Switch Motor Oil Viscosity in Different Seasons
Ask Your Stickiest Question. . . Or ask us something you’ve always wanted to know about using our products. We’ll sort through all the submissions and present the best questions to our automotive experts. We'll share the questions and their answers here.
Why Switch Motor Oil Viscosity in Different Seasons
My '99 Grand Prix has the 3800 engine which calls for two different viscosity engine oils. 5W-30 when temperatures are below 32° and 10W-30 when temperatures are constantly above 32°. My question to you is the following: Since Mobil 1 5W-30 and Mobil 1 10W-30 have approximately the same cold pour temperatures, would it be okay to use 10W-30 year round? Coldest expected temperature is minus 20°.
-- Jim Dalrymple, Horseheads, NY
The key difference in these two viscosity grades of Mobil 1 does not necessarily lie in the Pour Point measurement, but with the results of an industry low-temperature viscosity test called the Mini-Rotary Viscometer (MRV). This test measures the ease of which an oil is able to be pumped around an engine at low temperatures. Mobil 1 10W-30 can certainly be used adequately in that temperature range, but we would recommend following your owner’s manual for viscosity guidance. By switching to a 5W-30 in colder seasons, when starting your car on a cold morning you are providing your engine with an oil which can be pumped more easily to the moving parts of your engine (5W-30 having a lower MRV viscosity than a 10W-30 at equivalent temperatures). Your owner's manual is calling for a 10W-30 engine oil in warmer seasons to ensure your engine is protected at elevated temperatures by providing a thicker oil film for protection.
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