Math pros, please help me measure my consumption.

[dx92beater]

Guys,

I am attempting to measure consumption on my Subaru, but I need some help.

I used to be great at math, but not so much any more. I'd like to use my existing method to ensure consistency but I am having a little bit of trouble.

Below is what I did:

So I measured the distance from the top hole of the L on my Dipstick to the top hole of the F on the dipstick at 20mm with dial calipers.

I took a 431.6 mile trip and found that the oil level had gone down by 10.2 mm.

By my calculations, the engine consumed 51% of one quart and went 431.6 miles. I could rest here and say that I got about 850 miles to the quart, but I'd like to know how to reliably and quickly determine how much oil I burnt using this method if I check the dipstick after say 300 miles and the oil had gone down 35%....just a hypothetical.

I marked the exact location where I nest the vehicle and I wait a few hours before checking the dipstick.

My math tells me that the vehicle went 854.57 miles on a quart of oil, but I am not sure how I reached that conclusion or if it is even right. I always approached math differently than most and was never able to explain how I did it and in turn was really unable to understand how others did it.

I am sure that there are other methods, but I'd really like mathematical help with this one. The intent of this thread isn't to discuss the actual oil burning of the engine either. I have another thread for that.

Thanks for your help.

 

[Nick1994]

The distance from F to L is not always 1 quart. It's different for every car.

 

[Wolf359]

You don't have enough data. You need to add 51% of one quart and see if that brings it up to the previous level that you measured. You are also assuming that the oil pan is symmetrical.

 

[slo town]

How do you know there is a linear relationship with respect top the oil level between Full and Add markings on the dipstick?

Scott

 

[Nick1994]

Originally Posted By: Nick1994
The distance from F to L is not always 1 quart. It's different for every car.
Here's a screenshot for the owner's manual to my car.

0.7 quarts for my car from L to F

 

[dx92beater]

Hmmm, for starters I don't know that the distance between F and L is one quart and I don't know that the curve is linear.

RATS...but thanks.

 

[dx92beater]

I had no idea that the owner's manual *might* give me that data. Let me check that out for starters.

 

[dx92beater]

Gosh even the FSM doesn't have that info. I wonder if the owner's manual has it....going to check. All valid points.

 

[dx92beater]

Owner's manual doesn't have that info either. It is an 06 Subaru Tribeca with 3.0 H6 ez30d engine. I did a quick google search and it says that *most* Subaru dipsticks represent one quart between Full and Add.....but I'd like something more concrete.

If I can somehow determine that the dipstick is 1 quart, how close can I get to determining consumption without making life too difficult?

Thanks again.

 

[raytseng]

you are making life too difficult. Just pour a measured amount of oil back in to get to full and boom you got the ratio of how much consumed/how many miles.

 

[tombo]

While it's true that there are a lot of unknowns, I think the original poster was really just interested in the math.

If you go 431.6 miles and depleted 51% of a quart, then you would go 846.3 miles using 100% of a quart. The math is 10.2 is to 431.6 as 20 is to X. You can write this as two fractions: 10.2/431.6 = 20/x. Then, you "cross multiply" the top number (numerator) of one fraction by the bottom number (denominator) of the other fraction, then divide by the other numerator. So, x= 10.2x432.6/20 = 846.3 miles. Sounds complicated, but if you just write it out on paper, it will make sense.

Now, if you used .51 quarts in 431.6 miles, you burned .51/431.6 = 0.00118165 quart per mile. So if you go 300 miles and the dipstick went down 35% of a quart, the math would be .35/300=0.001166667, which is slightly better than we would have expected, because the first measurement would predict 0.00118165 x 300 = 35.45% of a quart.

Or, you could just top up the oil every Saturday and call it a day

 

[dx92beater]

Originally Posted By: raytseng
you are making life too difficult. Just pour a measured amount of oil back in to get to full and boom you got the ratio of how much consumed/how many miles.


So very true! I'd have to do that anyways lol! I guess that I use the dial calipers on something more linear like the side of the bottle.

 

[dx92beater]

Originally Posted By: tombo
While it's true that there are a lot of unknowns, I think the original poster was really just interested in the math.

If you go 431.6 miles and depleted 51% of a quart, then you would go 846.3 miles using 100% of a quart. The math is 10.2 is to 431.6 as 20 is to X. You can write this as two fractions: 10.2/431.6 = 20/x. Then, you "cross multiply" the top number (numerator) of one fraction by the bottom number (denominator) of the other fraction, then divide by the other numerator. So, x= 10.2x432.6/20 = 846.3 miles. Sounds complicated, but if you just write it out on paper, it will make sense.

Now, if you used .51 quarts in 431.6 miles, you burned .51/431.6 = 0.00118165 quart per mile. So if you go 300 miles and the dipstick went down 35% of a quart, the math would be .35/300=0.001166667, which is slightly better than we would have expected, because the first measurement would predict 0.00118165 x 300 = 35.45% of a quart.

Or, you could just top up the oil every Saturday and call it a day

Haha! Thanks for the course, I appreciate it. I was scratching my head over this for a while. It might just give me something else to go on....at least a reference point! Looking forward to Saturday.

 

[dx92beater]

Glad I posted for another reason, at least 2 popular Subaru's dipstick range is 1.1 quarts....wow, thanks for letting me know that even that varies.

If I verify that the distance is 1.1 Quarts, I'll be a slightly happier camper...of course if I find out otherwise I'll be crying....or maybe the opposite applies lol

http://www.subaruoutback.org/forums/atta...level-check.png

 

[krismoriah72]

Let me add to your math equation..

I have owned 5 or so subarus over the past 20 years and I think its an anomaly to have an accurate reading on the dipstick. I can check it several times and get several different readings...its like a magic 8 ball at times.

In all honesty let me help you out. The mighty subaru engines consume oil. No matter how much you worry or spend towards it..it will consume oil. This fantastic engine doesnt really care if its a quart over or a quart low.

My advice. Put 2 quarts of oil in a safe and convenient place and keep an eye on things and add as needed.. you will sell this car due to being tired of its looks or mannerisms..and the next guy will put many many more miles on it.

Oil is cheap..math is hard. Drive the dang thing from point A to point B ..she wont let u down.

 

[ecotourist]

In my experience oil consumption isn't linear anyway.

When oil is new, an engine will use less than when the oil gets old.

When oil has been in use for some time and you go on a long run the first bit goes down fast (likely fuel or water boiling off) and then it slows down.

The practical way to find out how much oil there is between the marks would be to start with the engine at the add mark and add oil until it reaches the full mark. The amount you added is the amount of oil between the marks, generally about a quart (or a liter).

 

[dx92beater]

Originally Posted By: krismoriah72
Let me add to your math equation..

I have owned 5 or so subarus over the past 20 years and I think its an anomaly to have an accurate reading on the dipstick. I can check it several times and get several different readings...its like a magic 8 ball at times.

In all honesty let me help you out. The mighty subaru engines consume oil. No matter how much you worry or spend towards it..it will consume oil. This fantastic engine doesnt really care if its a quart over or a quart low.

My advice. Put 2 quarts of oil in a safe and convenient place and keep an eye on things and add as needed.. you will sell this car due to being tired of its looks or mannerisms..and the next guy will put many many more miles on it.

Oil is cheap..math is hard. Drive the dang thing from point A to point B ..she wont let u down.



Thank you.

 

[bioburner]

Did I miss or did anyone mention that taking measurement at cold or when hot will also change where the reading will be. My Transit will read in the middle of the marks when cold but dead on the high mark when taken when hot but having sat for 10 minutes. Just trying to get a feel for the engine that got replaced last week is probably the only reason I took more notice.

 

[bioburner]

Originally Posted By: bioburner
Did I miss or did anyone mention that taking measurement at cold or when hot will also change where the reading will be. My Transit will read in the middle of the marks when cold but dead on the high mark when taken when hot but having sat for 10 minutes. Just trying to get a feel for the engine that got replaced last week is probably the only reason I took more notice.

Sorry, I see that the screen shot says to check the oil when at operating temperature.

 

[dx92beater]

Originally Posted By: bioburner
Originally Posted By: bioburner
Did I miss or did anyone mention that taking measurement at cold or when hot will also change where the reading will be. My Transit will read in the middle of the marks when cold but dead on the high mark when taken when hot but having sat for 10 minutes. Just trying to get a feel for the engine that got replaced last week is probably the only reason I took more notice.

Sorry, I see that the screen shot says to check the oil when at operating temperature.

Yep, you did! My dipstick is 1 quart not 1.1...in this game I feel a bit better.