weight of oil determines mileage
 

I have been doing this for a while now and have the data.

As all of you know, I change my oil every 1000 miles for almost 8 years now. I was running 20-50 Castrol for the longest time. Then about 3 years ago I changed to 10-30 weight Castrol.

I am currently getting 23 MPG in the city.

My MPG goes down to around 18 to 15 city with 20-50 weight.

I also noticed the engine doesn't rev as fast with 20-50 but the oil pressure is somewhat higher.

I only think 20-50 is good for turbo engines. N/A do not need the 50 weight, it kills power.

Absolutely impossible. No way you goin' to drop 8 mpg with 20/50. I've kept records with '89TII since new. The car will not vary from 20 mpg if I use 20/50 or 10/40.
My wife's Z24, and my Grand Cherokee...Ditto.

Its not impossible.... Try it again and see.

Now if you are gonna say no change in mileage I am going to say thats is impossible. Everyone knows thicker oil takes more to push it around, it is also thicker, so that adds to the amount of drag created by the oil.


Thanks!

Impossible

okay.:cool:

GLHS, do you have the TII or NA?
I think that could make a significant difference
there isnt near the pressure pushing that oil around in a NA, so the difference in gas mileage may not be as noticeable

I had both types.

If you look at some of the synthetic web sites, they will say a possible 4% increase over conventional motor oils.
If you were achieving 20 mpg, using synthetic would get you 20.8 mpg.
I don't disagree the 20/50 causes more resistance over a 5/30,10/30 etc, but it would be negligible as far as mileage and performance. Now if you were in Alaska with temps, let's say, below freezing, the 20/50 is going to cause a great deal of resistance, esp. on start ups.