A reader asks: I use 5W-30 motor oil in my Infinti G35 during the winter and my owner’s manual suggests that it is suitable to use 10W-30 in warmer temperatures. Is there any real benefit to switching to 10W-30 in the summer and back to 5W-30 in the fall?
Answer: There is absolutely no need to switch to 10W-30 motor oil in the summer if 5W-30 is an acceptable grade for your engine. While some car manufacturers still advocate the use of 10W-30 (or even 10W-40) as an appropriate engine oil option for summer use, it is completely unnecessary.
Today’s 5W-30 motor oils provide consistent protection at both extremes of the temperature spectrum. During hot operating conditions, they are resistant to thinning out, breaking down, boiling off and degrading to the point where they might cause deposits. Remember also that a 10W-30 and 5W-30 are essentially the same viscosity at operating temperature, so there is no tangible advantage switching over to 10W-30 for summer driving.
There used to be a time when switching to a heavier motor during the summer was a necessity. Four or five decades ago, engine oil technology was far less advanced and engine tolerances were less precise. Thicker engine oil was needed in summer to combat wear and oil consumption. These thicker grades did not pump well in extreme cold, so a seasonal oil viscosity change was once a common part of regular maintenance. This habit does still linger, but today’s motor oils (especially synthetic oil) negate the need for a seasonal viscosity changeover in either gasoline or diesel engines.
Enjoy the convenience of keeping one engine oil grade on hand and take solace in the fact that using 5W-30 for year round use will not compromise engine protection in the slightest.