I've used 10W-40 in the summer for years, and 10W-30 in the winter. The manual for my new (to me) 1999 Chevy pickup says to use 10W-30 in the summer and 5W-30 if temps are going to be below 0 F, and it specifically states NOT to ever use 10W-40. Why?
Newer engines are designed to use lighter weight oils which have better flow both hot and cold.
10/40 is just too heavy for these engines, and you'll increase top end valvetrain wear as well as lose some fuel economy.
Gregg
Remember - If I sound like I know nothing about farming it's because I really don't!
Danny, since I live in Texas where it gets hot, I've used 10W-40 for many years in all my vehicles. However, my '99 F150 pickup calls for 5W-30 and my '01 Windstar calls for 5W-20 year round. I've been told (without knowing personally) that some of the oil passages, clearances, etc. are smaller and the lighter weight oil gets through better. The owner of one of the quick oil change places told me that the state highway patrol had been told their warranty would be voided unless they use 5W-20 oil in the squad cars even in the summer. I don't know where he got the information or whether it's right, but anyway, I've started using the 5W-30 in the pickup and 5W-20 in the minivan like the manuals call for.
My suspicion has been that using the heavier weight oils might very slightly affect the fuel mileage and that the manufacturers need to keep those "cafe" numbers up. I've forgotten details, but if I remember right, Exxon and one of the manufacturers had a little lawsuit over that topic when they first came out with Uniflow in the 10W-40 weight and Exxon won. Don't know how that would come out today, but see no need to take any chances.
Just had the first oil change in my '03 F150 last weekend. I asked for 5W-30, and they said okay. Then I looked in the manual and it says to use 5W-20 year round. When I drove in to the bay, they asked if I really wanted the 5W-30 or what was recommended, the 5W-20. I opted for the 5W-20. <font color="blue"> SOMETIMES </font color> I read manuals [img]/forums/images/icons/grin.gif[/img]
I have herd that there is some kind of a problem with the 10-40 breaking down real bad in the newer high load/high temp motors. Something about the wide spred of the weights. Wether its true, or not, I do not know. But 10-40 is kind of an "old tech" oil.
Paul Bradway
Why 5w rather than 10w
Simple 5w is thinner - taking less HP, better MPG giving the auto makers better CAFE numbers.
carl
</font><blockquote><font class="small">In reply to:</font><hr />
<font color="blue">SOMETIMES </font color> I read the manuals [img]/forums/images/icons/grin.gif[/img]
[/ QUOTE ]
Say it Ain't SO! [img]/forums/images/icons/laugh.gif[/img]
LOL!
Steve
A lot of the newer cars will pump up the lifters and float the valves with the heavier oils. They have closer tolerances than the older stuff so you don't have the leakdown. When Ford first came out with the 4.6 V-8 they had a problem with the oil filters balooning when people ran the heavier oils instead of what the manual called for.
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