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Old 12-31-2009, 11:38 PM   #1 (permalink)
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Filling oil just to min line? better mpg?

I have read around here though I can't remember exactly where that some people have gotten mpg gains by just filling their cars oil to the minimum line instead of all the way up to the full line on the dipstick.

Anyone have any info on this?

I don't exactly see how you would get better mpg cause I would assume the oil pumps at a consistent rate/pressure regardless of oil level in the reservoir.
Now I know that the oil does cool down while in the reservoir so unless the slightly warmer oil has something to do with an increase in mpgs such as lowering it's viscosity. I'm not sure.

Now I am concerned with any negative effects of doing this however I have the feeling the only reason that your oil gets filled to the max line or that there is a max line at all is to (a) Keep people from overfilling their cars oil.
and (b) Since the majority of people don't check oil levels in between fill ups that extra oil is to protect people with oil leaks or cars burning oil from blowing up their engines cause the oil only gets checked once every 5,000 miles. Just a hunch, unless someone knows better.

Now I know in my car the min line to fill line is probably a good 1/2 quart+ and I check my oil regularly so would catch any lowering of oil levels quickly.

Other then the savings of about $2.00 worth of oil with each fill up would there be any increase in mpgs?

Only reason I ask instead of simply looking for any improvement is that I finally started to do my own oil changes and with my first change switched out to Mobil 1 0W-30 Advanced Fuel Economy.

According to it's claims on it's web site's savings calculator vs conventional motor oil I should get between 0.85 (winter) - 1.1 (summer) extra mpg. Will report any findings in a seporate thread.

Added bonus is that I get to use better grade motor oil, quality oil filters made in the USA instead of the cheapest ones the shop could get it's hands on. I also save $5 per oil change by doing it myself even with paying the premium of higher grade products. I also get to get away from the wife and munchkin and pull out my old box of cassette tapes and blast them in the garage for an hour.

BTW, heated garage FTW!

Lifetime mpg

2012 mpg

Last edited by Fr3AkAzOiD; 01-01-2010 at 07:56 AM..
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Old 12-31-2009, 11:45 PM   #2 (permalink)
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Of course the oil pump/pressure lube system would not be affected.

Any gain would happen if, when the crankcase is "full", windage is occurring on the crankshaft, as well as more oil getting flung off rods and whatnot. If lowering it to "add" reduces windage there ya are. Running it at "add" is still safe to the engine but you may want to check level more frequently as the "cushion" is smaller.

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Old 01-01-2010, 04:02 AM   #3 (permalink)
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Some vehicles have windage trays, and oil squirters for the cylinder walls, thus negating the need for crank splash. Mazda used them in a few cars back in the day, and few now. Then someone went and made crank scrapers, just a few mm off the crank to clean most the oil off. Mostly done for HP, but I'm sure there was a FE gain as well.
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Old 01-01-2010, 05:47 AM   #4 (permalink)
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i would never risk it i like my car too much to starve it of oil

(No actual EPA numbers for car just used F/E numbers when i first got it)
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Old 01-01-2010, 08:13 AM   #5 (permalink)
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Wall Mart wanted $55 to change my oil with 0W30 synthetic, $10 less if I bought the oil there. $30 for conventional, also $10 less if I bought it there.

I asked them why they charged and extra $25 to pour synthetic oil in the car, and was told that was their policy.

I bought 10 quarts and 3 filters for $22 more than they wanted to charge for one oil change, and it takes less than 10 minutes to do it in my garage.

That's my policy.

It works out to something like $200 an hour labor to let them do it.

I take the old oil to my old shop where they use it in the waste oil heater.

The VX can be done on the ground without ramps or a jack.

I like it just below the full mark, and now I will probably change it when it gets to the low mark. Not sure how many miles than will be, since it didn't use any in 4k miles before.

Filling to the minimum mark would allow the oil to warm up faster. You could check that by measuring the time it took for your filter to get hot to the touch. It would help mileage slightly, but not very much.

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Old 01-02-2010, 12:51 AM   #6 (permalink)
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if you want to read much more into the subject, bobistheoilguy.com is a must visit.

keeping the oil on the lower side for a non-aggressive driver is probably perfectly safe. Keep in mind, you might have an engine platform that is not happy with this decision, I cannot answer specifically for that. I have an engine platform (early ford duratec) which has the known issue of oil starvation during sweeping right hand turns.... its just a badly designed windage tray. For me its just not worth it because if you monitor oil pressure you will see a drop off going up a freeway on-ramp.

I do have an engine that eats a bit of oil, and there is a mild mark in increase in mpgs when the oil level gets low (so much so that the tank milage logs tell me to check the oil levels).

And I highly support anyone doing their own car maintence, I personally am a big promoter of using a local oil shop for some fluid work. I am a car tinkerer and have several highly modified cars, but over the years they have been really sharp at picking out issues that strangely I never noticed. Its been a form of idiot checking for me... just my 2 cents.
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Old 01-02-2010, 09:46 AM   #7 (permalink)
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Lapointe recommended over filling by a quart or so...he was into gaining mpg for sure.
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Old 01-02-2010, 11:42 AM   #8 (permalink)
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At least on my Honda civic the high and low mark are about 1 quart of oil, half a quart lower and I'm to the tip of the dips stick a full quart low and the oil pump runs dry if I take a sharp corner.
Apparently it's "normal" for a new car to use up to a quart of oil between oil changes without anything being wrong.
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Old 01-02-2010, 03:27 PM   #9 (permalink)
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I can't see any advantage to being a quart low. But the disadvantages could be potential or actual. If you began losing oil for any reason, you are already a quart 'behind the curve'. Also, with less oil being in the system it will tend to become dirtier faster, simply because there is less volume of it in circulation.

OTOH, there is no known advantage to overfilling, either. You can't go wrong by keeping it full, or at least between the full and low marks.
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Old 01-02-2010, 05:30 PM   #10 (permalink)
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Running low can provide a benefit of windage, as was stated before, but most engines these days are designed to prevent crank splash anyway. The oil pump draws out a certain volume from the pan, so the level in the pan is lower when the engine is running than when it is parked, FYI.

Maybe in days of yore, when engines weren't really designed with windage and the like in mind, it would have been effective. The only real way to know if it will work on your vehicle is to try it for a few tanks, then "top off the oil" and try a few more tanks...

If you have an SGII, you can note your idle fuel consumption at the low mark, then add that last quart and note it again. If you see no change, it's unlikely that it's going to help at all.

Crank splash, at least on modern engines, does not oil the cylinder walls. The volume of misted oil floating like crazy in the crankcase because of the violent motion of air compression and expansion does it. Vacuuming your crankcase does not prevent this, either. There will still be oil flailed around violently.

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