Ted's formula

[Squishy]

If temperature is involved, would oil weight or pour point then have to be factored in, too? (i.e., a 0W- oil at -40F would protect a heck of a lot better than a 10W-).

You could factor that into C*, but that would make it a little less straightforward to derive.

 

[XS650]

If you are actually keeping track of fuel consumption, there is a simpler form of the equation based on gallons of fuel consumed that gives identical results.

Ted's equation
OCI(miles) = (C*)(aver.mpg)(sump-qts)(cubic inches/Hp**)

Simplified version
OCI (Gallons of fuel consumed) = (C*)(sump-qts)(cubic inches/Hp**)

For example, using ThirdeYe's numbers

Original method
Dino OCI = (50)(30.26)(4)(110/142) = 4,688 miles

Simplified method

Dino OCI = (50)(4)(110/142) = 154.9 gallons

The beauty of the simplified method is that Ted's equation actually is based on fuel consumed with some constants added. The simplified method shows you what that important number actually is instead of burying it.

 

[ProfPS]

I used the TBN for my computation from the PDS; it might not be 100% accurate but it should be close. I guess if the TBN is available, then my addition could be used otherwise go with the original formula.

This weekend I will spend more time and work with the TBN piece.

//

Interesting approach with going by gallons used instead of the old miles standard. I think that might me a better way to go because it will be closer to operating hours. Good idea (or as they say in the N.E. "Good idear").

 

[Georgiadave]

LOL. Did the calculations for my push mower. I'm not sure the formula holds, but I am entertained. 140 miles or 100 gallons.

 

[ProfPS]

100 gals! That's 400 qts. Since a typical push mower's gas tank is 1.6 qts that makes 250 fill-ups. I typically use 1 tank for my 45 min mowing which is one tank-once a week; that would make for an OCI every 250 weeks of operation or every 11,250 minutes of mowing or every 4.8 years if I lived in a climate for year-round mowing [did the calucaltions quickly so there might be an error - but we all get the point]. So much for the manufacturer's 25 hour OCI.

I could only imagine how many years the OCI would be with Grp 4/5 oil. I don't think the engine would last the OCI; oil is cheap enough to throw 16 oz away once a year.

I guess that the formula cannot be used for every gas powered engine. Anyone willing to calculate the OCI for their 4-stroke grass trimmer??

 

[BarkerMan]

A company that does brush clearing used tanks of fuel as the monitor for oil changes in their 4-stroke engines. The do kind of the same thing for 2-stroke engines but the intervals are tune up intervals, spark plug, fuel filter and air filter. For my weed wacker I monitor the air filter and as soon as it starts getting darker it gets a tune up kit.

 

[jackkpts]

I find this very interesting, but one thing strikes me about this formula. As I did this for my two main vehicles, a 4 cyl 2006 Accord and a 6 cyl 2005 Pilot, I see that my Accord can go 73% more miles than the Pilot. (Accord's factor is 143.83 * C, Pilot's factor is 83.05 * C).

So unless the sump capacity is much higher on a lower MPG vehicle, the OCI will always be considerably shorter than a higher mileage vehicle. Not sure I buy this. According to this formula, auto manufacturers should have significant differences in there OCI recommendations between SUVs and cars for example.

Wouldn't RPMs also play a major role in the effort an engine puts out that would not show up in MPG? My Pilot cruises at 70 MPH at 1,900 +/- while the Accord does 2,300.

Just an observation.

 

[Roger]

Ted knew what he was doing.

Synthetic Oil Life OCI Formulas

 

[ConfederateTyrant]

Ted's formula was also a safety point and he'd recommend a UOA if people wanted to go further.

If it is accurate, I should be able to get about 24,000 miles with the Amsoil HDD or 0w-30. Perhaps one day I'll try it out.

 

[crinkles]

this is a very interesting thread. I'm going to give it a go once I get all the info from my owner's manual... this is what makes this site great...

OK, using the Ted Kublin method from http://neptune.spacebears.com/cars/stories/interval.html

Durablend 10W-30 (TBN = 8) - 8,300 miles or 13,200 km

(manufacturer specs 15,000km intervals)

THe website notes that one should rather use an em[pirical value instead of actual virgin TBN of 12 for amsoil, 8 for M1 and 4 for conventional. Durablend is semi synthetic so I used 6

and got OCI = 6200 miles or 10,000 km.

 

[crinkles]

using XS650 simplified method - 336 gallons OCI

at 24.7 MPG this means 8,300 miles!

So - i reckon a 10,000km OCI is just about right for me using a good synthetic blend like durablend (I know some folks may object, but it agrees well with my engine). This would mean oil changes over time of about 6 - 9 months.

 

[crinkles]

on another point, whether this formulae are correct or not, it could be used as a tool to see whether the cost of synthetics are worth it.

If durablend can take me 8,300 miles, and M1 11,700 miles, the factor in cost should be no more than 1.41. Durablend costs me $32/5L, and M1 $90/5L - so it is too expensive to be justified...

 

[crinkles]

for all the "frenchies" out there i've set up the formula in metric units so you don't have to do all the convesrions on the individual inputs

181 x TBN x SUMP X (ENGINE/kW) X (1/LHK) = OCI (km)


SUMP = oil volume in L
kW = engine power in kW
ENGINE = engine capacity in cc or L x 1000
LHK = fuel consumption in L/100km

e.g. for my camry, based on TBN = 8 -
181 x 8 x 4.3 x 2400 / 118 / 9.5 = 13,300 km

I would incorporate a factor of safety of 1.33 if using virgin TBN numbers for the oil, equating to 10,000 km OCI for my car.

interestingly enough, valvoline synpower and durablend both have the same TBN (8) so there are obviously some benefits the formula isn't great on.