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Originally Posted by Xplorer01
how come u use 10w-30? my manual says use 5w-30.
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First, 5-30 isn't all that common around here unless you want to go to the dealer to get oil. Second, I've done a fair amount of reading on the subject. I can't possibly condense it all down into one or two paragraphs, but here are some of the "truisms" I've come to accept (in no particular order);
-> Changing your oil and filter every 3,000 - 5,000 miles puts you WAY ahead of a lot of people with regard to engine life no matter what oil you use.
-> The "weight" of the oil (viscosity) is essentially its' resistance to flow. The higher the number, the "thicker" the oil. Consequently, it's easier for the engine to pump "thinner" oil. (Imagine trying to suck syrup through a straw)
-> Regarding Oil Pressure; Since it's measured at (or near) the pump, it is NOT an indication of oil flow. Rather, it indicates how much work the pump has to do to move the oil. "Thinner" oil will require less force and the gauge will read slighly lower pressure.
-> 5-30 oil gives slightly better gas mileage (at least the way the EPA measures it for the manufacturer's window sticker). The manufacturers are PROBABLY more interested in putting a higher MPG number on the window sticker than in any minor difference in wear (and therefore engine life) that can't really be measured anyway because most people don't change their oil regularly. Recommending 5-30 instead of 10-30 allows them to put the higher MPG number on the window sticker.
-> Lastly, while I can't confirm it there are those who claim to know that say the following with regard to multi-viscosity oils; It's better to have a smaller difference in viscosity range (10-30 is 20 "points" whereas 10-40 is 30 "points"). With that in mind (and assuming you accept the notion) 10-30 would be "better" than 5-30 because 5-30 has a bigger spread.
So, bottom line; I use 10-30 because it's readily available, it is no worse for my engine (wear-wise) than 5-30 and I'm willing to "eat" the 0.2 MPG I might be losing.