Oil;; What Weight ??

[bachler]

I rebuild engines; Air cooled gets 20x40 oil. Water Cooled Gets 10x30 weight;; I bought a new Truck. (brand not important ) It said to use 5x20 oil I use 10x30; It now has over 132000 miles on the engine, Runs like new. The only differance I can tell in the weight of the oil . With 5x20 It will get about 1 mile better per gallon of gas; Now I do not if 5x20 would have been better or if the engine would have lasted that many miles. They were with 10x30.I just wonder if they are squezing a bit more HP out of the engine While sacraficing Longevety; What is RiGht;;

[Mekanic]

no they are no sacraficing Longevety the later engines are designed with tighter clearences for the 5w20oil. asfar as the increase in MPG that is usually whis driving this. The newer Hemis with the multi displacment system MUST have 5w20 in them for that mds to work like it should. some of the other newer engines need a specific weight of oil for variable valve timing to operate. 6.1 hemis (No mds) use 0W40 mobil 1 from the factory. i have heard that toyota and honda are experimenting with 0W20 and 0W10 for mpg reasons. that was a yearago i haven't heard anything about that latley.
on cold starts the 5w20 will flow faster than any 10w30. cold starts and cold running are where most engine wear occors.

[W4MBG]

my 2000 honda insight (i3) uses 0w20. the manual calls for 5w20 if needed. my dodge minivan (v6) and the rv (ford v10) both use 5w20. size of the engine does not matter. i just run what the factory says. never had an oil issue.

[AFChap]

Tighter clearances are why newer engines need 5w20 and other lighter weight oils. Heavier weight oils will not work as well. I used to use straight 40w in air cooled engines in hot weather. And I still run 10w40 in my '67 Ford pickup. But both the engine clearances and the quality of the oils have changed, and we old schooled guys need to make some changes in our thinking too !

[RustyJC]

My Acura 3.2TL-S specified 5W-20 oil. Back when I bought the car new, 5W-20 was still hard to find, so I substituted 5W-30 Mobil 1 synthetic in its i-vTec V-6 engine. Fuel mileage dropped about 1 to 1.5 MPG in commuting service, and the engine felt "rougher" and sounded mechanically louder. The next oil change, I chased down some Royal Purple 5W-20, and the fuel mileage immediately returned to normal, and the engine operation was noticeably smoother and quieter.

I'm old enough to come from the day when we put 20W-50 racing oil in our hot street engines, thinking that it could withstand the stresses better than the then-commonplace 10W-30 oils. As has been mentioned, times have changed, and the manufacturers have set engine clearances and selected oil pump volumes and pressures based on their recommended lube oil viscosities. Change comes hard, but this old codger learned his lesson.

Rusty