I thought this was interesting and wanted to share it here and get some opinions. Even though I have used, and will continue to use, 5w-20 in my '04 Mazda6i I'm not sure I agree with their spec as stated in the owners manual.
From page 8-10 of my owners manual under "Recommended Oil";
"Engine oil viscosity, or thickness, has an effect on fuel economy and cold weather operation (starting and oil flow). Low-viscosity engine oils can provide improved fuel economy and cold weather performance.
But high-temperature weather conditions require higher-viscosity engine oils for satisfactory lubrication."
I found this interesting that they mention benefits in fuel economy and cold weather operation with low viscosity oils (surprise surprise) but when it comes to "satisfactory lubrication" in high temps they admit higher viscosity oils are needed. Now the part that suprised even me (a 5w-20 proponent) is the small graphic under the quoted passage which shows a thermometer with scale from -30f to 120f and directly under it another graphic with text that states 5w-20.
Now I'm usually one to adhere to manufacturer specs but could this really be accurate? Would someone who lives in an area that routinely reaches those high temps be safe using a 5w-20? I imagine driving in rush hour, stop and go traffic in 110f weather with 5w-20 dino in the sump and I must say it doesn't give me a good feeling.
On the same page there is a large box with a bold "CAUTION" which reads; "Using oils of viscosity besides those recommended for specific temperature ranges could result in engine damage."
So with their words they are dangling the carrot of using a different viscosity oil but at the same time making the recommended temperature range for 5w-20 so broad that most people in north america would be going against their recommendation by doing so. Also the fact that the only mention of proper lubrication is with higher viscosity oils makes one wonder.
The plot thickens (so to speak
)
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