There are so many variables that you really need to find an explanation for how reducing the oil below the recommended level would increase mpg. Or, you need to duplicate the experiment enough times that you average out the other factors.

People have listed some of these factors such as ambient temp., use of AC, driving conditions (traffic, number of green lights vs. red lights, etc.), tire pressure, driving habits (of which the driver might not be an objective enough to evaluate), and I've probably forgotten some.

Changing the oil, noticing falling mpg, removing oil, seeing your mpg rise -- this is not enough to establish cause and effect. There easily could be some other cycle of events causing a dip and then rise. If you had worn blue socks and noticed the mpg go down, then worn grey socks and seen the mpg rise, would you attribute the mpg to the color of socks?

I've not heard this. Can you point me to the proof of this fact?

Or, perhaps they are filling the down pipe. Perhaps the pump is not well calibrated (enforcement is rather lax in many places). Perhaps the MINI tank is actually larger than the manual states. Perhaps there are a number of factors involved.

 

overfilling can result in alot of issues, one of them is unbalance of the loads, i would also assume that sufficient filling can cause too much pressure head on the pumps and resistance to rotation. I have some documents at home from SAE that dictate the effect of overfilling, i can look those up.

Cranks normally do not sit in oils baths, but in some cars it can easily be the case if over fill (some have the baffle pans), it would be safe to assume that if the crank was actually making contact like a propeller in the water then yes you could get foaming, but at that point you would probably have other issues as well.

 

Sure, depending on what you consider proof...

"When temperatures rise, gas expands, so in extreme heat consumers do get less at the pump than what is paid for"

Source: http://www.10news.com/investigations...96/detail.html

 

That is what is known as hearsay evidence, not fact. If the "consumer groups" are correct, they are talking about 2-3% which doesn't get you from 13.2 gal, to 15 gal.

 

You didn't ask for proof of how much gas expands, just that it does. If you don't like my evidence, Google away to your heart's content. For some reason you have a desire to contradict anything I say. Started with your 'Made in Germany' MINI oil, and has continued ever since. If you don't like what I have to say please just skip over my posts. Or provide some proof that I'm wrong.

 

Sorry if I'm bugging you. It isn't anything personal. It's just that the claims:

1. An oil changed caused mpg to drop.
2. Filling the oil to the high mark on the dipstick causes lower mpg.

go against common automotive lore.

Also understand that the subject of oil changes tends to be a controverial one on NAM. You made some fairly outragous statements about a controversial subject. As others have said, you seem unwilling to listen to the other possible causes of your mpg change.

 

Without any engineering knowledge or evidence, I could guess that viscousity (sp?) of new oil could make it thicker and, thus, require the engine to strain more. On the other paw, the new oil should better lubricate and, thus, put less strain on the engine. I believe it is possible that the confidence and smoothness of the new oil causes you to drive more aggresively and that causes the drop in MPG.

 

I wonder. I lost mileage a few days after I noticed this and reseated it.



Could I have been leaking air into the system that may have done some damage? I'm still fighting to get more than 25mpg average. The other day I was doing steady 65mph on the interstate and still barely getting 30mpg. It just doesn't seem right.

 

i also am victim of a dealer overfilling my oil. i took a 300 mile road trip today and was getting 29ish MPG with a light foot. i used to get 34+. my oil level is almost an inch above the max oil line on the dipstick. otherwise the car dives fine.

 

Except mine wasn't overfilled. It was just below the full mark (or right at it) and I removed about 8oz of oil and now it is right at the halfway point between full and add marks (which I figured would be if I removed 16oz of oil). I'm still averaging around 25mpg where I used to get 28-30.

The car also doesn't seem to have the punch it used to. Odometer is at 4000. Tires are at 37PSI and I'm using 91 octane (name brand).

 

sounds like you have a different problem all together then. hope you figure it out. sounds turbo related. on a side note, i noticed my engine as its breaking in has had decreased milage. NO LIE at 3000 miles i got over 40+ MPG on a highway trip, and now im getting 30 if im lucky. weird because i always thought engines get increased mileage as they broke in.

 

try a OBD2 reader to see if it is throwing a code.

 

Is that something the dealer has? Or can one be found elsewhere?

 

Many auto supply stores can do a read for you. Or, you can buy a device your self. Or, get a ScanGaugeII and have a boost and water temp readout for your car.

 

Looks like a cool little tool. Is it worth spending the extra money on the ScanGauge, or are the $60 tools just as good? With the lack of gauges on the MINI, seems like it might be worth it.

Do you have one? Where is the OBD connector on the MINI? Will it fit in the little cubby below the radio?

Thanks for pointing it out. As usual, I'm back in the Middle Ages when it comes to tools and current technology...

 

I got the ScanGaugeII so I could see water temp and boost (MAP). I have it sitting on top of the dash (Velcro). It displays four items from the OBC at a time. So, you can see water temp, boost, mpg, and mph. Press one of the buttons and you can change one to other readings. The only things it doesn't have, that I would like, are oil pressure and temp. Perhaps the OBC isn't measuring them?

The connection is under the dash just to the left of the steering column. It has a plastic cap on it.

 

Gas pumps in the U.S. aren't temperature-corrected, but they are calibrated for volume, so if they say they dispensed 10 gallons, they dispensed 10 gallons, regardless of what the temperature of the gasoline is. On a hot day, that 10 gallons will have less mass than on a cold day, but the number of gallons that you can fit into a particular-sized gas tank doesn't change with temperature.
__________________

 

In the owners manual on Page 98 it shows the location of the OBD2 connector.

 

I'm not sure there's that big of a difference between filling up in the am
vs in the heat of the day. The tanks are underground and don't heat up
markedly over the course of the day. If you feel the metal part of the
pump, you notice it's often cooler than the heat of the day after the first
half gallon or so goes in. So ground temp (which changes slowly over the
seasons, is more important than air temperature. Once the gas gets in the
car tank, however, it will equilibrate more quickly, but then it's already been
measured by then. and can expand about .3 gal per tankful with a 50 degree
temp change
I beleive about 50 degree F change in temp is about 2.5% change in density
for gasoline, and much less for a steel gas tank, don't know about plastic
tanks.

 

Oh, you're absolutely right - there's very little change in the density of gasoline, even over wide temperature swings. 2.5% over 50F sounds about right, because I know it's only 6% over an 80F range.

The whole "you're better off filling up in the morning when it's cooler" thing is the same story that's trotted out each year when the weather starts to turn hot by journalists/reporters that have a limited understanding of science.

The point of my post was just that (in the U.S. at least), the number of gallons that you can fit into your car while filling up doesn't vary with temperature.

Also, even on a hot day, you still get "all the gas you paid for", because gas is advertised "by the gallon", it's sold "by the gallon", and the number of gallons dispensed is accurate regardless of temperature.

 

So could you just tell me where that location is, or do I have to go get my owners manual?

 

Here it is:



Basically, it's in the driver's-side kickpanel, almost up under the dash, but not quite.

 

Thanks. I thought my mother had come back from the dead to tell me "Look it up in the dictionary!" whenever I asked how to spell something. I don't know how she'd be able to torture me now that there are spell checkers.

 

Just to see if my fuel efficiency is still there I drove around very gently shifting around 2000 rpm every gear. I drove both in the city traffic and more free way and after about 70 miles I was getting 36.2 mpg. Last time I filled her up the manual calculation was only 0.3 mpg lower than the computer. Therefore, I was actually getting about 35.9 mpg. I couldn't be happier.

 

I have also noticed a decline in fuel mileage, and on cooler mornings the car would run rough for about 45 seconds when first started. Made a 240 mile trip weekend before last and only averaged 29.8 mph . Thats bad. Usually I average 34 mpg or better on this same route. Saturday I filled up with unleaded plus instead of premium, and drove almost the same route. I averaged 34.6 mpg. The car hasn't run rough yesterday or today when first started either. Very interesting . . .