My OCI formula: when the voices tell me to. Or at least a majority of them...
Calculating OCI
- Thread starter ka9mnx
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Hard no on that rule of thumb. The gas tank size is an independent variable.
It's because we calculate fuel economy in miles per gallon, not miles per quart, and we describe oil pan capacity in quarts. However if you know your oil pan capacity in gallons, then you can save yourself that little bit of arithmetic.Makes people feel special and they can proclaim "yeah, I used a complex mathematical formula consisting of multiple variables that optimally calculates my oil change interval requirements".
I first saw this formula described by @Hohn here.
OP could have just said "change your oil after you've burned 200x your oil pan capacity in fuel," but he rightfully likely realized that calculation is probably beyond the average person's math ability, so he wrote out the formula to make it easy and show how he arrived there, and you guys assume the worst. Didn't your math teachers make you show your work? If he just used 50, you guys would be saying "why 50?" smdh Everyone's a critic.
My formula has never failed: OCI = 5,000.
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I don’t think this is a good example. That’s a tiny turbo engine in a midsize suv going OLM intervals (likely 10k) on vwb. Surely a port injected Toyota engine on 5k is much easier on oil.
Patman
Staff member
My GM and Honda oil life monitors have never failed me. The engineers did a great job coming up with the algorithms there. It has saved me a lot of money in oil because I have been able to go much longer than 5k oil changes in both.
At least the formula gives sane ranges. Run the formula with your minimum MPG and maximum MPG. It makes sense that on the same vehicle, more MPG=more highway miles=longer OCI.
2003 Civic - I've never gotten lower than 26 mpg in the winter with lots of idling, but I average 30 overall and get 38 on long highway runs.
3.5*200/4*26 = 4550 mi
3.5*200/4*30 = 5250 mi
3.5*200/4*38 = 6650 mi
So if my commute increases, the formula sanely increases the OCI. If I'm short-tripping and idling a lot to keep my car defrosted, it sanely lowers my OCI.
2018 CRV - averages 24 mpg in a mostly short-trip environment, but can get 33 mpg consistently on long road trips.
3.7*200/4*24 = 4440
3.7*200/4*33 = 6105
Because the CRV is such a huge fuel diluter, I'd drop the values by 25% to account for fuel dilution. That's just my gut talking. So,
3330 mi OCI on the low end, and 4600 mi on the upper end.
2013 Volvo S80 - averages about 22 mpg in mixed driving, but will sustain 28 mpg on the highway
7.2*200/4*22 = 7920
7.2*200/4*28 = 10080
Now, lets peek at Blackstone's Universal Averages for these vehicles. This is the average healthy, normal OCI for each engine whose sample was sent in for analysis.
2003 Civic = 5800 mi
2013 S80 = 6800 mi
2018 CRV = 5300 mi
The Volvo Universal Average does not line up with the formula as well as the other two. But Volvo themselves recommend 10000 miles or 1 year for this vehicle, which does line up with the formula.
I'm not saying anything other than the formula outputs sane ranges of values when you consider driving style and conditions.
2003 Civic - I've never gotten lower than 26 mpg in the winter with lots of idling, but I average 30 overall and get 38 on long highway runs.
3.5*200/4*26 = 4550 mi
3.5*200/4*30 = 5250 mi
3.5*200/4*38 = 6650 mi
So if my commute increases, the formula sanely increases the OCI. If I'm short-tripping and idling a lot to keep my car defrosted, it sanely lowers my OCI.
2018 CRV - averages 24 mpg in a mostly short-trip environment, but can get 33 mpg consistently on long road trips.
3.7*200/4*24 = 4440
3.7*200/4*33 = 6105
Because the CRV is such a huge fuel diluter, I'd drop the values by 25% to account for fuel dilution. That's just my gut talking. So,
3330 mi OCI on the low end, and 4600 mi on the upper end.
2013 Volvo S80 - averages about 22 mpg in mixed driving, but will sustain 28 mpg on the highway
7.2*200/4*22 = 7920
7.2*200/4*28 = 10080
Now, lets peek at Blackstone's Universal Averages for these vehicles. This is the average healthy, normal OCI for each engine whose sample was sent in for analysis.
2003 Civic = 5800 mi
2013 S80 = 6800 mi
2018 CRV = 5300 mi
The Volvo Universal Average does not line up with the formula as well as the other two. But Volvo themselves recommend 10000 miles or 1 year for this vehicle, which does line up with the formula.
I'm not saying anything other than the formula outputs sane ranges of values when you consider driving style and conditions.
It is contrived. Every calculation on this board with this formula is approximately 5K miles.
Its a contrived formula from the start - designed to get somewhere near 5K miles - ie the illusion of precision.
Yeah, it's a horrible example. Honestly Valvoline shouldn't even have published this video. I suspect they ran it this way because if the conventional / blend was changed at 5k (instead of 10k) the results wouldn't be nearly as dramatic - meaning less views.
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I totally agree with this. A seen the UOA of a friend who installed a bigger oil pan on his GR86 with track duty. Exactly as one would expect, his peak oil temps decreased considerably (since not the whole oil can hold more heat per temperature), and it sheared considerably less, even slower than mere proportional increase would suggest, i would speculate thanks to the more stable temperature. Needless to say, now there is more oil to dilute contaminants.
Though on a car that tackles short city driving would not probably be benefitted from it as now the car would be spending more time with cold oil
It helps with actual mechanical shear?
that makes no sense, a 60 mpg vehicle needs 4x shorter oci than a 15 mpg vehicle with the same sump size
is it really? the vehicles with large tanks tend to have big engines with big oil sumps
Just in: look what the forum favourite has to say about mpg and oil changes.
I have the video start right at the relevant quote
OK, who here is buying a MTM SLIM? Inquiring minds want to know.
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Lol, your posts always crack me up. Of course you know very well that oil shears faster if it is cold, and its rock stable if it is hot
Yeah yours crack me up too.
Still confused about shear heating in a bearing and permanent shear loss due to VM cleaving I see.
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Or rather still believing that temperature can effect the speed of chemical reactions
"Tend" is the key word. Cars are not built to a specific tanks per mile specification. Some go 180 miles on s tank, some go 600 miles, and that holds true for big vehicles, little vehicles, old, new, whatever. Likewise, the amount of oil in the sump varies on a lot of factors, beyond needing a certain amount of oil to suspend particles and deliver lube, conduct heat, supply additives over a period of time. I would allow that sometimes sump capacity get small as engines get smaller, have fewer cylinders. I'd also suggest that you can insert a Chinese Wall between DI and non-DI engines. Beyond that, there are outlying engines that probably have much higher or lower sump capacities that they might seem to need, like older Jags, Porsches, Subarus, big block V8s and others. Enough pieces are moving that it adds up to a sizable issue using sump capacity in a rule to apply across the board.
I too have placed faith in the Honda monitors. My last GM car was a 1976 Chevette, so no experience. I do think suggesting that the Honda OLM's are driven by much of an algorithm is generous. I find that they are entirely predictable, more or less driven by mileage, and very hard to parse. For example, in one Honda we currently have, the monitor goes from 100% to 90% in 300 or so miles. Then, every remaining 10% increment gives you 750 or 800 miles. You might think that that increment would increase with highway mileage, but it doesn't. Still, no complaints. I change that oil usually at about 20-30%, somewhere a little over 6,000 miles, but could not see anyone getting in much trouble following the OLM. Just not thinking that there is much going on in the OLM's "brain."
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