# Oil Change Calculators

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http://neptune.spacebears.com/cars/stories/interval.html

Have fun

Post if you get results that are close, or comically off.

Cheers, 3MP

Thanks for the link, it's very interesting reading. I tried the calculator based on Kublin's method (#5) and for both my vehicles it came up with ~3k intervals for dino oil.

Very cool! I'm getting about 6-7K oil change interval with all the calculators (1.8l turbo engine).

I assumed the TBN of virgin M1 5w-30 is 13. Does anyone know how much it really is? I noticed on 3 Mad Ponchos' page they show TBN as high as 15.5

What about TBN of virgin M1 0w-40?

Thanks!

For my 2002 Subaru WRX I get the following recommendations:

Theory 4: 4786
Theory 5: 6611
Theory 6: 8158 given constant
Theory 6: 3574 personal constant

I think they all would work, but to be on the safe side if I had to choose one I would choose the most conservative. The differences are certainly eye opening, disregarding the first result from theory 6, the low estimate is roughly half the high estimate.

Very interesting reading. I'm thinking that in the wife's Chevy my 4K interval with 5w30 makes some sense. I am going only 3K with the 5w20 in my Ford just to be safe.

I don't recommend using the TBN as one of the variables in this formula for two reasons:

1) TBN is not linear parameter, ie a 9 TBN oil will NOT last 75% as long as a 12 TBN formulation. In fact, it will probably last significantly less than 50% as long.

2) TBN retention varies quite a bit from oil to oil - two formulations with the same initial TBN will not necessarily hold up the same.

A more general form of the equation I proposed would be:

Drain Interval (in miles) = (C*)(mpg)(qts of sump capacity)(cubic inches/Hp)

C* values:

120 for Amsoil or Redline
80 for Mobil 1 or Schaeffers S7000 blends
40 for an average petroleum oil

I realize the units don't come out in miles when you multiply these variables, so treat them as dimensionless constants.

The initial equation has been derived emperically ...in other words it is based on drain intervals I have been able to run with Amsoil in various applications.

TooSlick
Dixie Synthetics

TBN is definitely not linear, and as said varies considerably with the brand, injector cleanliness, fuel, blow-by, and many other factors.
I think Load, RPM, and total revolutions is a better idea, but of course hard to extrapolate between users. The built in lights are a good start towards this end, but the dealers can program the base mileage, so you might have differences between two identical cars driven the same but set up by different dealers.

Well, I did the calculations by TooSlick's formula and came up again with 3k oil change intervals for dino oil. What are the 3k oil bashers going to say, the formulas are all wrong?

quote:

Originally posted by Green Max:
Well, I did the calculations by TooSlick's formula and came up again with 3k oil change intervals for dino oil. What are the 3k oil bashers going to say, the formulas are all wrong?

3k with dino oil is fine, I just have a beef with those doing 3k changes with synthetic! Although that means I need to be mad at myself, as I just drained out Royal Purple 5w30 at 2600 miles this afternoon in my wife's car. I wanted to start a fresh test with Royal Purple now that our cold weather is gone, to see how this oil can compare to the Mobil 1 she ran last year from April to November. And from now on my plans for her car are to do two oil changes per year, one right before winter hits, then one right after the cold weather goes away in the spring. So her winter oil will usually only have 3k on it, but her summer batch will be closer to 5 or 6k.

Green Max, as the site points out, the formulas could indeed be entirely wrong.

The formulas often generate wildly different results for the same car... they can't all be right.

Cheers, 3MP

Patman,

You kill me. You drain Royal Purple at what, \$8/quart (2600 miles?) just to "start fresh". When your not doing this, your running all around Canada looking for Castrol 0W30! I'm glad my obsession for motor oil is not near as bad as yours!

quote:

Originally posted by ryansride2017:
Patman,

You kill me. You drain Royal Purple at what, \$8/quart (2600 miles?) just to "start fresh".

I got a case of Royal Purple for free, so it was \$0 per quart.

I know it sounds silly that I drained it so early, but it was the first run with a new oil, plus it was run through a nasty cold winter, and I want to have a good long run on Royal Purple in her car in non winter weather to see how good the UOA looks.

I tried the last formula.
And with leaving a small reserve in TBN, with my compression and bore I got between 2700 and 3400 miles interval.
(depending how much TBN I was willing to start w/)

Fred...

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