20W50 costs 1.5mpg over 10W40?

vwlover77 · Post by **vwlover77** » Wed Apr 08, 2009 8:00 pm

For the first full 3000 mile oil-change interval after my engine redo in late 2007, I ran 10W40 oil and averaged 18.6mpg with a maximum of 20mpg and a min of 17.5mpg.

I then changed the oil to 20W50. I'm about 2000 miles into this oil change and now averaging only 17.1mpg with a maximum of 18.1mpg and a min of 16.2mpg.

I guess it could be that the first 3000 miles took place in warmer weather overall than the second 2000 (I do not have an operating thermostat right now). Or would the difference in oil viscosity alone cause this mileage difference? Or, maybe it's a combination of lower temperatures AND heavier oil?

static · Post by **static** » Wed Apr 08, 2009 8:22 pm

Correlation does not equal causation.

spiffy · Post by **spiffy** » Wed Apr 08, 2009 9:26 pm

There are soooo many variables that it would be impossible to say.

However, I think the oil flavor would not affect your carbs or injection. Just sayin.

vdubyah73 · Post by **vdubyah73** » Thu Apr 09, 2009 3:59 am

If it's still cool in the morning when you start up your MPG is going down due to the heavy oil at warm up. Bet your cold idle is lower also. Been running 10w30 in the winter and 20w50 in the summer. My summer mileage is better than my winter. In the spring, with the 10w30 still in it, MPG gets better. In the fall when still running the 20w50 my MPG goes down. When it's cold out my MPG can get as bad as 14 MPG, even with 10w30. I've gotten as good as 19 1/2 MPG in summer. Crux of the biscuit is, ambient temp and the weight of your oil has a lot too do with MPG.

Post by **Amskeptic** » Thu Apr 09, 2009 8:30 am

vwlover77 wrote: I guess it could be that the first 3000 miles took place in warmer weather overall than the second 2000

Don't blame the oil. When 20 50 is at summer operating temperature, it is as runny as 10-40 is in spring temperatures. Temp sensors 1 and 2 will knock your mpg down in a hurry when it is chilly out. And did you adjust your tire pressures when temps dropped? You can lose up to three psi in the tires when temps drop by 5-10* and that will also reduce your fuel mileage.
Colin

dtrumbo · Post by **dtrumbo** » Thu Apr 09, 2009 9:36 am

vwlover77 wrote:... and now averaging only 17.1mpg with a maximum of 18.1mpg and a min of 16.2mpg.

I'm glad I'm not the only one getting these less-than-stellar fuel mileage numbers. I run 20W50 year round (it rarely gets cold here) and I see my mileage vary seasonally. I blamed it on the winter-blend-ethanol-crap gas you get in the winter, but I really don't know what the real cause is. Like Static said, correlation is not causation.

Post by **Amskeptic** » Thu Apr 09, 2009 11:53 am

dtrumbo wrote:
vwlover77 wrote:... and now averaging only 17.1mpg with a maximum of 18.1mpg and a min of 16.2mpg.
I'm glad I'm not the only one getting these less-than-stellar fuel mileage numbers. I run 20W50 year round (it rarely gets cold here) and I see my mileage vary seasonally. I blamed it on the winter-blend-ethanol-crap gas you get in the winter, but I really don't know what the real cause is. Like Static said, correlation is not causation.

Rat thar nuther varee able. Ethanol reduces efficiency by what? 5%?

TrollFromDownBelow · Post by **TrollFromDownBelow** » Thu Apr 09, 2009 3:00 pm

Had an old Chevy pickup with loose main bearings. Ran 20w 50 and would get approx 18mpg. Switched to a 'cocktail' of 20w50 and 5w30 and picked up approx 1.5 mpg. Nothing else changed; same time of year, same gas, etc. Not a controlled test on A/C VW's, but on my h2O cooled V8 there seemed to be an effect.

vdubyah73 · Post by **vdubyah73** » Thu Apr 09, 2009 3:01 pm

Takes longer in cool/cold weather for everything to warm up. If your commute is 25 miles it may take half that to warm up in the winter. If it's cold it may not reach full operating temp at all. In summer weather you may be fully warmed up in less than 5 miles. This includes the gear oil in the tranny. Cool/cold weather definitely effects mileage. Now a couple hundred miles on the freeway, the difference in MPG will diminish. Thats why gas mileage advice always recommends combining errands into on trip.

Post by **Amskeptic** » Thu Apr 09, 2009 4:47 pm

vdubyah73 wrote:Takes longer in cool/cold weather for everything to warm up. If your commute is 25 miles it may take half that to warm up in the winter. If it's cold it may not reach full operating temp at all. In summer weather you may be fully warmed up in less than 5 miles. This includes the gear oil in the tranny. Cool/cold weather definitely effects mileage. Now a couple hundred miles on the freeway, the difference in MPG will diminish. Thats why gas mileage advice always recommends combining errands into on trip.

With my trip computer on the BMW, I have always seen a drop in fuel mileage based on weather even with the switch to 10-40. In frigid upstate NY January long distance driving, I'd get 24-25 mpg tops. Temp sensor I reads incoming air regardless of engine temperature. Cold weather drags wheel bearings and differentials too.
Colin

Hippie · Post by **Hippie** » Thu Apr 09, 2009 6:35 pm

I thought modern German cars used, like, XW-60 wt. Maybe that's with turbos.

vwlover77 · Post by **vwlover77** » Fri Apr 10, 2009 8:59 am

I'm also wondering about not having a thermostat. In cold temps, say 30 degrees F, is it possible that the thermostat would not be fully opening the flaps on an hour-long highway trip? Wouldn't think so, but I'm curious!

TrollFromDownBelow · Post by **TrollFromDownBelow** » Fri Apr 10, 2009 9:14 am

don't forget the affect of air/fuel mixture too... colder air = denser air, therefore more fuel is needed to maintain the same ratio. Took a trip out west once in my FI s-10 pickup. At the higher elevations (thinner air) I noticed about a 20% improvement in gas mileage compared to when I was traveling at sea level.

So in summary:

Cold weather = decreased mpg for all reasons everyone has listed
Thicker wt oil = decreased mpg for all reasons everyone has listed

I believe that you will sacrifice a few $ in lost mpg for running thinner oil in the summer, but your engine will last longer and burn less oil if you run thicker (20w50). My 2 pence.

TrollFromDownBelow · Post by **TrollFromDownBelow** » Mon May 18, 2009 5:01 pm

thought id unearth this thread.... Recently switched from 10w40 to 20w50. All I can say is wow! was burning 1 qt every 250 miles ... just checked the oil, and it's just slightly below the full mark after 240 miles.... I'm guestimating a qt every 500 to 750 ... maybe better.Don't know how much is the quality of oil vs weight (cheap 10w40 vs castrol 20w50) ... but I'll take it!

Hippie · Post by **Hippie** » Mon May 18, 2009 6:59 pm

Could be both. I seem to see a difference in consumption with different brands of the same weight.

Itinerant Air-Cooled

Itinerant Air-Cooled

20W50 costs 1.5mpg over 10W40?

20W50 costs 1.5mpg over 10W40?

Re: 20W50 costs 1.5mpg over 10W40?

Re: 20W50 costs 1.5mpg over 10W40?

Re: 20W50 costs 1.5mpg over 10W40?