[V8] Causes of Bad MPG?

[Scott Simmons]

A 5W30 weight oil will have the same thickness in the summer as a 10W30, 
a straight 30, or a 0W30.  They all have the same viscosity at high 
temperatures.  The difference is that a 5W30 will be thinner at colder 
temperatures than a 10W30, but thicker than a 0W30.

This is why I recommend 0W40.  It has the incredible thinness of a 0 
weight oil when the car is first started (winter or summer) which allows 
for quicker oil pickup to those bearings during the first revolutions as 
well as less of a battery draw.  Ever notice how the engine hates to 
turn on cold mornings?  Thin the oil and the engine will respond 
faster.  It also will hold up like any 10W40 or 15W40 at high 
temperatures.  I've never needed anything thicker than 40 weight (except 
in a 904...) even in triple digits.  For Arizona-esque climates, a 5W50 
by Castrol would be a good choice, as those areas might require the 50 
weight in the summer.

While poor oil viscosity choice can cause bad gas mileage, I don't think 
it would be to the extent that is the case (that started this thread).

~Scott Simmons

dsaad at icehouse.net wrote:

>As long as you are in the warmer part of the state, I don't see much problem.
>I have run Delo 400 15W40 in every car I ever owned and year 'round. It has been
>a problem only a few times in the below zero weather, but that does not happen
>too often now-a-days - what with the global warming and all :-)
>
>I do have a case of 5W30 oil for my next change though. It is the recommended
>oil for the Explorer, and I figured I would try it in the V8 just for fun.
>As luck would have it, we are scheduled for a cold snap starting tonight - and
>tonight is when I plan to change it. Should be fun. They are predicting hi teens
>temps with wind chill at -20 in the high country.
>I would have a hard time using the 5W30 in the summer though. It just seems too
>light - even though Ford says it is fine. I have never had a oil related failure
>in any motor.
>(and that includes the time I tore a hole in my Jeep oil pan while fighting a
>giant sagebrush)
>
>
>Dave
>
>  
>