Further discussion on OCI alternative

[ProfPS]

Since last March's thread on Ted's formula ( http://www.bobistheoilguy.com/forums/ubb...rue#Post1100111 ) I have given more thought to OCI's based on gallons of gasoline/fuel used instead of miles traveled. Since running hour meters are not readily available, this approach is closer to engine operating time than driving distance/odometer OCI's. I found Ted's formula interesting, but I was looking for an easier approach to calculating fuel used (gals) based OCI's. Looking at two realistic extreme OCI conditions and the OCI durations for each, I calculated the number of gallons used for each OCI condition.

The two conditions used were best case all highway driving and worst case all city driving OCI's for my '07 V6 Rav4. Using dino, my OCI's would be 6k and 3k respectively and using OTC syns would be 7.5k and 4k. I know there are other variables such as season of the year, number of cold start-ups, and idling duration to name a few, but I was looking for an easier calculation to use for my OCI's.

I typically get 17 mpg all-city and 32 mpg all-highway driving. I have only used dino and I don't know what syn mpg's would be. I have achieved 34 mpg's on the highway several times, but 32 mpg is more common. Here are my calculations:
dino | syn
OCI: 3000 6000 | 4000 7500
mpg: 17 32 | 17 32
gal used: 176.4705882 187.5 | 235.2941176 234.375

Based on this approach, my dino OCI would be 180 gallons and my syn OCI would be 235 gallons (rounded to the nearest 5 gallons). I would recalculate my syn OCI after using it and seeing if there is a mpg change.

Each car would different based on actual mpg's and owner's OCI's. What are your fuel used based OCI's?

 

[TeeDub]

One of the main reasons the formula was configured the way it was is so that you don't have to keep track of total # of gallons of gas consumed during a particular OCI (which no one does), nor do you need an hour meter on the vehicle. In fact the only parameter that changes with the same vehicle is fuel efficiency, which is highly dependent on the current duty cycle for the vehicle. So if your daily commute changes significantly, you'd want to recalculate your OCI given your new fuel efficiency #. I'd also argue that the power density (Hp/Ci) does come into play, above and beyond the fuel efficiency of the vehicle. These multivalve, high rpm, high compression and/or turbocharged engines (V-Tec, VW/Audi Turbo, etc) seem to beat up the oil even if you drive conservatively with an eye towards high fuel efficiency.

BTW, the idea of using TBN x (10) in place of the C* constant is NOT very accurate, since different chemistries perform all over the place in terms of TBN retention. For example, I think the new API/CJ-4 formulations do better in this regard than an 8-10 TBN, CI-4 oil would....

 

[Cup of Joe]

Ted's formula perfectly mirrors my used oil analysis results not all of which are posted. My current fill of ASM should last 15k miles. To verify I will be testing at 10k miles as a check up on the way to 15k. I look forward to TeeDubs input in about 3 weeks.