[joegeeZe]

I did an oil and filter change about 2 weeks ago and I noticed that my gas mileage has been shitty since then.

I bought the oil from my dealer, so it should be the same as what was already in there, its a CPO car.

So, does anyone know if after an oil change, a break in period is required for these cars or for the particular type of oil I used? It was the BMW Synthetic SAE 5w-40 type.

[Tom K.]

Are you sure you didn't accidentally disconnect something - a vacuum hose, perhaps?

Tom

[joegeeZe]

Originally Posted by Tom K.

Are you sure you didn't accidentally disconnect something - a vacuum hose, perhaps?

Tom

I dont think so..I'm not experienced when it comes to these kinds of things, but I doubt I did something like that.

[328i]

My guess is it's the oil you used. If by Freehold you mean Freehold NJ then I would not use a 5w40 oil especially in the winter since that's a fairly thick oil. I would recommend 5w30 instead.

[joegeeZe]

Originally Posted by 328i

My guess is it's the oil you used. If by Freehold you mean Freehold NJ then I would not use a 5w40 oil especially in the winter since that's a fairly thick oil. I would recommend 5w30 instead.

Yes its Freehold, NJ. I never had a problem with gas mileage, I actually do almost 350-375 miles on a full tank, routinely. Thats a mix of highway/city driving too.

But, now it seems like Im not getting the same gas mileage after changing the oil for the first time since I owned the car.

It would make sense to assume that 5w-40 was already in the car when I bought it right? I'm going to switch to Mobile 1 regardless, but just wondering if theres a problem. I monitor how many miles I do on a full tank every week so this week will be no different. I guess I'll have to wait and see.

[joegeeZe]

Originally Posted by TrackRat

5W-30 and 5W-40 are year round oils for all climates. If you took an extreme example of a conventional 5W-40 and a high mpg energy conservation approved 5W-30 oil, you would typically see a 3% difference in the EPA test cycle. Real world you would typically see half of that or 1.5% diff. We don't know how bad "shitty mileage" actually is but unless it's ~ 1.5%, then the issue ain't likely to be the minute diff in hot oil viscosity between 30 and 40 weight, which can both have a hot viscosity of 12.5 cSt. or the identical viscosity @ 212 F.

Its far more likely that a change in Winter fuel mix, weather, driving conditions, etc. accounts for any significant change in mpg if there is nothing mechanically wrong with the vehicle such as a bad injector, low tire pressures, etc.

http://www.ideas4ag-ed.com/uploads/3..._viscosity.pdf

The only thing I did differently was add a bottle BMW Fuel Cleaner to the tank (had 1/8th of a tank of gas left) after the oil change. I filled the tires to correct presures, filled up on the same gas I always use, didnt drive any diffferently and I actually drove one day less than I normally do because I worked from home.

So, everything is the same except I changed the oil and added that bottle of cleaner. If I had a bad injector, how would I know?

[Tom K.]

Last time I checked, BMW synthetic 5w30 was actually cheaper from my dealer than Mobil1. And 5w30 Mobil1 is not approved by BMW for your car. I'm south of you and have used only BMW 5w30 for about 10 years in various BMWs with no problems whatsoever.

BTW, how are you calculating fuel mileage? If you are using the OBC, have you double checked it for accuracy? Do you reset it at each fillup? Are the driving conditions before & after the oil change the same?

Lots of variables here.

Tom

[joegeeZe]

Originally Posted by Tom K.

Last time I checked, BMW synthetic 5w30 was actually cheaper from my dealer than Mobil1. And 5w30 Mobil1 is not approved by BMW for your car. I'm south of you and have used only BMW 5w30 for about 10 years in various BMWs with no problems whatsoever.

BTW, how are you calculating fuel mileage? If you are using the OBC, have you double checked it for accuracy? Do you reset it at each fillup? Are the driving conditions before & after the oil change the same?

Lots of variables here.

Tom

I meant Mobile 1 0w-40 is what Im going to use. I am using the OBC and have not checked it for accuracy. However, I drive the same amount of miles every week, more or less, and I am resetting it everytime I fill up. Yes, the driving conditions before and after the oil change are the same.

All variables are basically the same, I didnt change anything except the oil and drive one day less. So, thats why I think the gas mileage is suffering a bit, it just doesnt add up.

I guess I'll have to see what happens at the end of this week...

[hipnotic]

none is needed