# Oil Weight?



## AZdriver (Sep 8, 2005)

I live in a part of the world where the summer daytime temp often hits around 110º, with a low in the mid 80's. Winters rarely drop below 32º. The manual indicates that for higher temp climates, 10w40 is the appropriate oil. Will a 5w30 provide insufficient hot weather protection, especially at sustained highway speeds, and is the 10w40 heavy enough to impact gas mileage in 'cooler' weather?


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## abmobil (Nov 22, 2004)

If you want to use a 40 weight during summer months,Mobil 1 truck and suv 5w40 would probably work well in the 4.0


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## Bror Jace (Apr 26, 2003)

I've seen even a 5W-20 work well in your neck of the woods. Check this UOA from a Ford Expedition of all things:

http://theoildrop.server101.com/ubb/ultimatebb.php?ubb=get_topic;f=3;t=002811 

However, every engine design is a little different. I'd feel better with a thicker oil in your motor, especially when the manual recommends a thicker oil in elevated temps. And, you are not getting much, if any benefit, from the thinner oils at start-up. It just doesn't get cold enough to tax your engine that way.

Typical 10W-40 oils would probably work OK for you. They are not terribly shear stable so after 1,500-2,000 miles, they will be shear down to a stable 10W-30. That's just about ideal for most passenger car or light-truck engines.

Yes, you will probably see a slight decrease in fuel economy ... maybe as much as 2-3%. I think that's worth it if a UOA with the thinner oil showed elevated wear.


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## ittamaticstatic (Nov 5, 2003)

good question but there has been a lot of oil weight threads.


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## himilefrontier (Jan 21, 2003)

The thing you have to remember is that a modern 4 cylinder engine is not a small blcok V8 from the 50's-80's. The internal tolerances are MUCH tighter and specifically designed for low viscosity oils ( some as low as 0W-30!). Running too thick an oil could starve the bearings because it is not able to pump it in the bearing clearences. If you are concerned about lubricity and film strength, a good synthetic like Redline , Royal Purple or Mobil 1( my favorite) will take care of that , and give you much longer service life.I have 225k on my Frontier and run 5W-30 all the time. No problems at all.Plus, the lower viscosity oil will use less gas and have less parasitic drag inside the engine. The only way I would run a thick oil is if the engine was old and the bearings tired, so that I could push it a little while longer before a rebuild. So, save the 40 weight, 20W-50 etc for the smoking 305 in your 1987 Caprice wagon, because that's the ONLY place it belongs.


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## Bror Jace (Apr 26, 2003)

*himilefrontier*, I don't think engine tolerances/clearances have changed much in the past 10-15 years. 

The trend is towards lighter and thinner oils with heavier anti-wear packages for the economy reasons you cited above ... 

... and as I have stipulated above, all PCMOs (Passenger Motor Car Oils) tend to shear down a full grade from their starting point. A 10W-40 is not a 40 weight at temp for long ... maybe 1,500 miles. Then it's a solid 30 weight from that point until it's drained ... well-suited to most automotive applications.

You'd be in no danger of starving your motor with a 10W-40.

But I agree that going even thicker (like 20W-50) or the straight weights can be detrimental ... possibly even increasing wear a bit. Economy will likely suffer as well.


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