Oil viscosity vs MPG

[kkspeed]

I am curious about the effect that oil viscosity has on MPG.

I currently drive a 99 Civc which calls for 5-20W oil. However, I have been using Valvoline Full Synthetic 10-30W since I get it for free.

Can 10-30W reduced my gas mileage? It sounds a little silly considering that the car is driven in 95+ degree temperatures (outside).

Any opinions? Thanks!

 

[Steve S]

Probably not enough to offset the free oil .

 

[mechtech]

ditto

 

[dave1251]

On a civic no way.

 

[daemonite]

my friend made the switch to a 5w30 dino, made at most a 1mpg to 3mpg difference.

I lose or gain that much just on the inflation pressures of my tires or the gasoline I use that week.

 

[radiometer]

After years of 5/10W-30 in my 99 Nissan Sentra I switched to 5/10W-40 several years ago. On road trips I keep a detailed record of fuel used. I actually 'gained' a little MPG.

I also very recently changed the 02 Nissan Sentra to 5W-40 Schaeffers 9000 synthetic. There is no difference in MPG on this one. It's my wife's dailey driver and she has been sensitive to fuel economy with this car and has noticed some difference between gasoline brands. There is no difference in fuel use in this car with the heavier oil.

I look with curiosity at reports on this board of engines being bogged down with 30 or 40 weights. I don't know why my two engines handle the heavier weights better than reported by other owners, but these two have shown no difference in performance. As noted above, one of them is getting improved MPG with it.

 

[z917990]

I'm pretty sure that Honda did not start calling for 5w-20 in their cars until 2001, so your '99 Civic should be fine on 10w30, as long as the outside temp is above 20 degrees F. I really would not use 5w-20, even if it did give you a little better gas mileage, because Honda recommends 5w30 for your engine all year round, or, as mentioned, 10w30 if the temp is over 20 degrees.

 

[airbus]

I've switched back and forth (5w20/5w30) and haven't really noticed any difference.There is one exception. Torco SR1 5w20 did result in slightly better mileage. It's a very low viscosity 5w20.

 

[Raven18940]

I went from 5w30 to 5w-40 and noticed no drop, but I do all city driving and get my foot in it quite often. If all these light weight oils are for fuel economy like we all think, how much are they actually gaining from them?

 

[Dr. T]

They had 5-20 in `99? Hmm.. Anyways, they probably use 5-40 in Japan, so I wouldn't sweat it....

 

[tenderloin]

My sons Focus 2.0 showed a difference on MPG when using GC (went down). To me it makes sense that a smaller, high winder would/could be influenced by a heavier oil.

Also to me, 1-3 mpg is substantial..others may disagree. Hard tires and put-put driving also help, but I choose not to go that route...just my choice.

 

[427Z06]

Why not try an OCI of Valvoline Full Synthetic 5w-20 yourself and see what results you get? Different engines, driving styles, climates will all influence whether you'll see a difference or not.

 

[JAYCEE]

Stick with the free earl.

 

[kkspeed]

I'm looking at all angles because the city MPG is disappointing; 25 mpg city. I believe that it is rated at 30 mpg city per EPA. It only gets 25 mpg when I drive strictly in the city on short trips (< 5 miles). My 88 Civic got about 28 mpg in the city. Once on the highway the MPG shoots up to 37 mpg.

I guess this version of Honda's 1.6L with an automatic is not as efficient as the older 1.5L
in the 88 Civic.

 

[Raven18940]

I wouldn't say it's less efficient, just your 99 is many hundreds of pounds heavier. The old EF civics were feather weights, where as the newer civics are only light weights. If you're getting 37 mpg on the highway I'd say you're doing just fine. On throttle driving, aka city, is very dependent on weight.

 

[Blake Sobiloff]

quote:

---

Originally posted by krholm:
After years of 5/10W-30 in my 99 Nissan Sentra I switched to 5/10W-40 several years ago. On road trips I keep a detailed record of fuel used. I actually 'gained' a little MPG.

---

I have experienced the same thing in my Infiniti QX4 (Nissan VQ35DE engine). I'd been running Mobil 1 5w30 but decided to try Shell Rotella T 5W-40 for this OCI. I've actually gained a little over 1 MPG and I'm even doing more short trips during this OCI than during the previous OCI.

I think the Nissan engines (at least the VQ series) really like a thick 30-weight or a thin 40-weight oil.

 

[moribundman]

I got some of the best gas mileage with Syntec 5W-50.
One slightly underinflated tire will probably make bigger difference in gas mileage than oil that's a little thicker.

 

[darkdan]

Going from 5w30 to 5w50 on my little 63 hp engine (a stiff wind means the cars top speed is 65 mph) resulted in a 11% decrease in mileage.

So I'm guessing on an engine with more power it wouldn't make as big of an impact.

After all, I increased my operating vis by 165%! That's a lot of extra work for my little motor.

But I agree with the rest....free is free.

 

[nickmckinney]

I think its more of how much city driving you do. I found little to zero change highway, but significant enough changes city with the lower viscosity that I use it myself.

 

[Doc Holiday]

car makers recommend thiner oils to help them with CAFE (corporate average fuel economy). If they can get .5 to 1 more mpg out of a car then that helps them alot. Don't you find it strange that Ford is saying to use 5w20 even in some car that the year before it said 5w30, and no engine mods were done with the model change. You don't see the guys a indy useing 5w20