Mixing Chevron Supreme 10w30 with 10w40 OK?

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Apr 13, 2003
I just bought two cases of Chevron Supreme 10w30 but I still have about five quarts left over from a case of Chevron Supreme 10w40. Would it be a good idea to mix one or two quarts of 10w40 with 10w30 in a five quart capacity engine? I have a noisy(valvetrain) DOHC 3.2 Isuzu engine with a belt/gear driven cam arrangement and I figure the thicker 10w40 oil would help quiet down the engine while still having the fuel economy of using the 10w30 oil. Any suggestions/comments?
Well..it may quiet things down but really won't help preserve the life of the timing chain. And if its a belt it won't help that (obviously). But there's no harm in mixing in Hawaii (warm)
Under warranty I use whatever the book says to use. After warranty I swap out 1 qt of 20w50 for 1 qt of 10w30 in my chevy trucks. My Nissan truck took 10w40 until about 170000 miles, now it takes mixed (1)10w30 and (4)20w50 ..(has 192000 miles on it now) Swapping out a qt of 10w40 for a qt of 10w30 should be no problem at all, probably never notice that you did it. Main problem with the 10w40 is it has alot of the VII that can break down under high heat and longer OCI, but reasonable use is not a problem.
I mentioned the belt/gear drive arrangement because on this particular engine, a crank driven belt turns a pulley on each head which is connected to a small drive gear that drives the two cam gears. I'm concerned that all these gears plus the loose valve clearances would shear down the straight 10w30 oil quicker.
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