MPG drops after oil change

It will recover after you change the oil again, but with 5W30.

JeffD

 

Also, be sure you are staying under the fill mark on the dipstick.

 

On the highway once the engine is warmed up, there's no real difference between a 5W30 and a 10W30. So it's likely that your very small change in highway MPG is either a random variation of a minor difference in oil formulations that's unrelated to the grade.

For short trips however, where the oil often doesn't properly warm, then yes it's likely that 5W30 will give a small boost in fuel economy over 10W30. How much depends on just how cold it is where you live and how short are your trips.

As pointed out above, double check to make sure you're slightly under the full dimple on the dipstick for best fuel economy. Overfilling the oil can add extra drag.

BTW. What brand/product oil did you use, and what was your previous fill?

 

I agree completely except for your first sentence. There is a wide variation of the allowable viscosity of xW-30 oil at operating temperature. It can run from 9.3 to 12.5 cSt at 100C (212F). 12.5 cSt is 34% more viscous that 9.3 cSt. For a comparison of a random pair of 5W-30 and 10W-30 oils, either one could give better fuel economy at operating temperature.

 

Yeah I didn't explain it very well because I didn't want to get too technical, but that's what I meant when said "minor difference in oil formulations". That includes other things as well, like different additive pack and friction modifiers, but I was thinking primarily of within grade viscosity variations when I said that.

 

I would be using 0-20. That is all my cars have ever used. H

 

I really like Toyota brand 0-20 synthetic and it is reasonably priced. Here in Canada around 6.50 per ltr. .H

 

Ok, thanks for the info. Both Valvoline and the Mobil-1 line include several different full synthetics, but the regular Mobil-1 10W30 should be pretty similar to the regular Valvoline Synpower 5W30 at normal operating temperature.

From their relevant technical data sheets:

Synpower 5W30 viscosity: 10.7 cSt @ 100C and 59.5 cSt @ 40C

Mobil-1 10W30 viscosity: 10.1 cSt @ 100C and 63.2 cSt @ 40C

So Mobil-1 10W30 is actually slightly thinner at 100C than the Valvoline 5W30 and so theoretically (all other things equal) should give slightly better highway mileage (if viscosity were the only factor).

Are you sure you didn't use the high mileage version of the Mobil-1? That one's quite noticeably thicker, especially when cold.

Mobil1-HM 10W30 viscosity: 12.0 cSt @ 100C and 78.1 cSt @ 40C

 

It is my belief that defrost always runs the A/C to dehumidify the air.