# Oil Change Formula

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#### TooSlick

I have been playing around with the idea of predicting a good initial oil change interval for Amsoil in new applications. This formula is based on three main variables: specific fuel consumption, sump size in comparison to a 5 quart reference sump, and power density, ie Hp/Cubic Inch. Note: for diesel engines I'd use ft-lbs of torque instead of Hp.

The simple formula I came up with, based on analysis results of Amsoil in other applications, is to change oil when total fuel consumption for the drain interval =

600 gallons * sump capacity in qts/5 qts * cubic inches/HP

If we take my new Audi TT quattro, we have the following variables:

27 mpg average
4.8 qt sump
108 Ci
225 hp

600 gallons * 4.8/5.0 * 108/225 =

600 gallons * .96 * .48 = 276 gallons

276 gallons * 27 miles/gallon = 7452 miles between changes. So I'll test the oil in my new TT for the first time @ 7500 miles and go from there ....

The nice thing about this formula is that it takes into account variations in driving conditions. For example, stop and go driving and short trip driving in cold weather are very hard on the oil. These conditions also result in poor fuel efficiency. Highway driving at moderate speeds is ideal for fuel efficiency, and also promotes long oil life....

You can adjust the number of gallons you start with for other synthetic or petroleum oils and use this formula the same way ....

TooSlick

quote:

Originally posted by TooSlick:
I have been playing around with the idea of predicting a good initial oil change interval for Amsoil in new applications. This formula is based on three main variables: specific fuel consumption, sump size in comparison to a 5 quart reference sump, and power density, ie Hp/Cubic Inch. Note: for diesel engines I'd use ft-lbs of torque instead of Hp.

The simple formula I came up with, based on analysis results of Amsoil in other applications, is to change oil when total fuel consumption for the drain interval =

600 gallons * sump capacity in qts/5 qts * cubic inches/HP

If we take my new Audi TT quattro, we have the following variables:

27 mpg average
4.8 qt sump
108 Ci
225 hp

600 gallons * 4.8/5.0 * 108/225 =

600 gallons * .96 * .48 = 276 gallons

276 gallons * 27 miles/gallon = 7452 miles between changes. So I'll test the oil in my new TT for the first time @ 7500 miles and go from there ....

The nice thing about this formula is that it takes into account variations in driving conditions. For example, stop and go driving and short trip driving in cold weather are very hard on the oil. These conditions also result in poor fuel efficiency. Highway driving at moderate speeds is ideal for fuel efficiency, and also promotes long oil life....

You can adjust the number of gallons you start with for other synthetic or petroleum oils and use this formula the same way ....

TooSlick

Well..trying to be objective.
The units dont come out right the 600 gallons should be 600 gallons*cubic inch/HP. Also if you divied the 600 by 5 and add the appropriate constant you would have:
120 gal*cubic inch/(HP)(qt.)(mpg) x sump capacity x HP/cubic inch x Average mpg

Problem is that you don't really know if the constant is right (120) - but as you said-you could adjust. Also I'm doubtbul about the HP per cubic inch. For instance my Sentra has 140 HP/123 cubic inches =1.14

So mine is 120 x 1.14 x 4 x 28 = 15,321. That might suggest that the HP/cubic inch needs to go away. Good start though
I think the miles per gallon is a very good factor.

[ March 03, 2003, 10:22 AM: Message edited by: Al ]

TooSlick,

A good start. The emprical Constant may have to derived emprically and you may want some kind of severity factor S.F. (unlike fear factor
) included that divides the result so as to decrease the mileage interval. Maybe a table of three or four S.F's that describes what value to use with what driving severity.

I think anything you might come up with would be better than blanket declarations of 25 or 35k for any and ALL vehicles.

A modern Japanese 600cc sport bike would be:

115hp
3.2qt sump
36.6 ci
45 mpg

600 x .64 X .32 = 122.2 gal

5500mi

what is the conversion factor of liters to CI. Most if not all engines today are listed as L not CI? Can you provide the formula to convert? For example, I have at least two 3L engines, one 3.2L, one 3.8L and One 2.0 L? Does a turbo affect the calculation?

[ March 03, 2003, 12:05 PM: Message edited by: Spector ]

Maybe the formula should take into account what the owners manual recommends.

For 3 of my vehicles I get a range of 80% to 300% of what the manual recommends.

[ March 03, 2003, 01:07 PM: Message edited by: satterfi ]

62 cubic inches to a liter (close enough anyway).

IMO the critical flaw in this equation is the assumption that engine contaminants are a direct reflection of engine load and performance. Unfortunately, some engines are just plain dirtier than others.

It would be very interesting to start applying that formula to cars here on this board that undergo oil analysis already. Then we could track how effective the formula is. Maybe you should set up a webpage with the data.

Cheers, 3MP

14,321 miles for me

1 L = 61.02 cubic inches (in.^3).

1 US Fluid gallon = 231 in^3 or 3.8 L.

2002 Subaru WRX

5qt sump
121c.i.
227hp
~20mpg

600*(5/5)*(121/227)
600*1*.533
319.82*20mpg

6396 miles per oil change

TooSlick, brilliant work man. In my testing with 3000 mile oil changes it has been clear that much more is available in the oil. As my car is turbocharged and high reving(like your specific output monster
), it seems that a mid 6000 mile interval is the safest maximum time.

[ March 03, 2003, 01:46 PM: Message edited by: nicrfe1370 ]

1999 Toyota Camry V6 (W/ Eaton M62 Supercharger)

5.0 Qt Sump
183 c.i.
242 HP (4.5# boost)
26 MPG

600 * (5/5) * (183/242)
600 * 1 * .76
456 * 26
11,856 miles

Amsoil labels my engine as "mechanically unsound" so you might want a "does not apply to the Toyota 1MZ-FE" disclaimer in here somewhere.

Discalimers are for people who are incabable or unwilling to think for themselves or take responsibility for their actions.
I don't mean to sound like a jerk, but that's the way I feel.

'02 Grand Cherokee 4.7L V8

600 * 5.75/5 * 288/235
600 * 1.15 * 1.23 = 848.7

848.7 * 17mpg= 14,428 miles intervals !!

4.7L V8 * 61.4(roughly) = 288.58 ci
235hp
300ft/lbs torque
17mpg average

If Jeep would warranty 14,000 intervals, I'm sold!

On my Audi 2.7t, this works out to 11,545 miles - not too far from the factory-recommended 10K change interval; interesting.

i have math. for division me awalys forget which number to put in first.
the first time i did it it got like 30K between changes.
the second time i got 500K between changes.

107ci
75hp
42mpg
4.5qt sump

p.s i think this test needs to take into account the operating tempature of the engine. take me aforementioned volkswagen sandrail for example, its got a cam, higher than stock compression, and some slick valve work to get it from 65hp to 75. but it is not uncommon for vw aircooled engines to see operating tempatures of 350-400F. this extreme heat literally cooks the oil in the heads. undoubtly adding to the stress on the oil. therefore, a similar sized and hp water cooled engine would probably go alot longer per oil changes.

[ March 03, 2003, 07:08 PM: Message edited by: cryptokid ]

quote:

Originally posted by nicrfe1370:
Discalimers are for people who are incabable or unwilling to think for themselves or take responsibility for their actions.
I don't mean to sound like a jerk, but that's the way I feel.

Should have put a
after my comment about an Amsoil disclaimer for the Toyota 1MZ-FE. Terming an engine "mechanically unsound" is a way to weasle out of a "warranty" in my opinion. No way, no how would I ever run oil in my 1MZ-FE over 11,000 miles (as the formula results showed for my case) before an analysis.

Yea, my V6 92 Camry (grandfather of the sludge factories so to speak) 3LV6 would calculate out to be in the 11,000 mile range also. Oil analysis has shown that 7500 miles is about right for a change on it.

Now, on my twin turbo
600 X 1. X 180/320 @ 22 mpg = 7,000 miles.

Maybe, but I go one year or 5000 miles whichever comes first

I hate it when this happens. Mu above post was screwed up bc I divided HP by cu in
Hate it wnen you can't edit
. No wonder my Sentra went 15,321 instead of 11,800 (Thats better).

TooSlick pointed this out to me in a PM instead of Publicly Bashing me
I deserved the public bashing
.

Sorry about that Al. We do have the edit feature available but limited for 30 mins after the post. Guess in this case it wouldn't have help'd. Nice to know you make mistakes like me. No harm there.

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