Calculating OCI

ka9mnx

ka9mnx

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Came across this formula in, either, a thread here or in a paper. Cannot remember. It works for the vehicles in my fleet.
Probably posted in the wrong forum.

qts x 200 / 4 x mpg =

This is for my Ranger:

5qts x 200 / 4 x 18mpg) = 4,500 miles
 
7,500 mile OCI for my Mazda 3. Exactly what is in my manual for normal.

7,500 mile OCI is what is the "Normal" range in my owners manual. Severe service is 5K, so that is what I follow. No need for a formula. If it's a concern, just follow severe maintenance schedule. Looks like your formula works though.
 
That thing has been floating around here for a while in one form or another.

The Critic

Thread 'OCI Formula'

https://bobistheoilguy.com/forums/t...ultimate-oil-change-strategy.2637/#post-35025

@TooSlick came up with this formula many years ago. A few of us were around when this formula was discussed. Curious if anyone still uses it or feels it is relevant in this current environment.

Formula: OCI = (C*)(ave mpg)(sump in qts)(cubic inches/Hp)
C= constant which was derived by Tooslick's opinion from reviewing UOA's; he was using a "120" for Amsoil and "80" for synthetic oils such as Mobil 1.
C

Thread 'Using fuel use to determine oil change interval'

I've seen it mentioned many times that using fuel consumed to determine when to change oil is a possible method along with hours and miles.

So what exactly is the formula here?

I presume we need:

Gallons of fuel consumed
Sump size
Engine size

Once we have that info, what calculation do we perform?
T

Thread 'Oil sump size and OCI'

WOW! I thought my sump was small as it takes 4 quarts with the filter. I would 2nd the recomendation on synthetic and 4000 miles changes then do an oil analysis. You can probably go more miles but an oil analysis will tell you how you are doing.
 
dnewton3 said:
Ehhhhh ... Why "200 / 4"? Because "50" was too easy?
Click to expand...
There is actually a name for this - "illusion of precision".

If you make it more complex it appears to be more believable, like someone did extra work figuring it out. Rather than just a random number like "50"

Why would MPG matter for OCI? Unless you have a diluter which is an entirely different issue?
 
dnewton3 said:
Ehhhhh ... Why "200 / 4"? Because "50" was too easy?
Click to expand...
And why are the number so nice and round? Why not 215? Or 187?

I totally agree that the volume of motor oil an engine holds, should be a consideration in OCI. Diesel trucks have used large volumes of motor oil to hold soot in suspension, and lengthen the OCI.

But the 200 and 4 just seem to be contrived.
 
SC Maintenance said:
Why would MPG matter for OCI? Unless you have a diluter which is an entirely different issue?
Click to expand...
Higher fuel consumption correlates pretty well with low engine temperatures, more idle time, more city driving, and more contamination of the oil with combustion byproducts. These are all things that oil life monitors take into account to adjust the oil life estimate. Basing OCIs on fuel consumed should work pretty well as a poor man's OLM.

I'd use this formula though:

(Actual Mileage) / (EPA Combined Mileage Rating) * (Manufacturer Recommended OCI) * k

where the value of k depends on what type of BITOGer you are. k=0.5 for the obsessive compulsive over-maintainers, or k=2.0 for the HPL fanboys.
 
trd1zz said:
But not modern conventional / synthetic blend?
Click to expand...
I wouldn't push a synthetic blend to 5,000 miles in severe duty applications.

And when you consider the fact that "conventional" oil no longer exists and it is all a synthetic blend and then you consider the benefits of a full synthetic and the fact that the prices are very similar it makes almost zero sense to use a synthetic blend except in very few cases, I believe some early 2000s Subarus had issues with full synthetics.
 
Furious said:
I wouldn't push a synthetic blend to 5,000 miles in severe duty applications.

And when you consider the fact that "conventional" oil no longer exists and it is all a synthetic blend and then you consider the benefits of a full synthetic and the fact that the prices are very similar it makes almost zero sense to use a synthetic blend except in very few cases, I believe some early 2000s Subarus had issues with full synthetics.
Click to expand...

Even when the synthetic blend meets the manufacturer spec?

For example - there's tons of early to mid 2000's Toyota motors out there running 5w30 synthetic blends for the full length of Toyota's recommended 6mo/5k interval. I personally own 2 of them. They are doing just fine.

Take your Toyota with a 5w30 specced motor to The Car Care Nut and he is going to put in 5w30 Toyota Genuine oil (which apparently is synthetic blend) - no questions asked.
 
trd1zz said:
Even when the synthetic blend meets the manufacturer spec?

For example - there's tons of early to mid 2000's Toyota motors out there running 5w30 synthetic blends for the full length of Toyota's recommended 6mo/5k interval. I personally own 2 of them. They are doing just fine.

Take your Toyota with a 5w30 specced motor to The Car Care Nut and he is going to put in 5w30 Toyota Genuine oil (which apparently is synthetic blend) - no questions asked.
Click to expand...
Your Toyota that has been running 5w30 synthetic blend its whole life for 5,000 mile intervals might be running good but it is not perfectly clean inside nor is it as clean as it would be if it was running a full synthetic its whole life. There is just no argument out there that can magically make synthetic blend a better oil than full synthetic.

I have 2 Toyota's myself.

As for The Car Care Nut, he knows how to fix Toyota's and does an excellent job at it but he knows nothing about oil, he is a Toyota purest who thinks only Toyota/OEM fluids and parts are the best.
 
Furious said:
Your Toyota that has been running 5w30 synthetic blend its whole life for 5,000 mile intervals might be running good but it is not perfectly clean inside nor is it as clean as it would be if it was running a full synthetic its whole life. There is just no argument out there that can magically make synthetic blend a better oil than full synthetic.

I have 2 Toyota's myself.

As for The Car Care Nut, he knows how to fix Toyota's and does an excellent job at it but he knows nothing about oil, he is a Toyota purest who thinks only Toyota/OEM fluids and parts are the best.
Click to expand...

And the real world implications for (theoretically) not being as clean as it could / would be, (besides looking cleaner), is? Because I had the valve cover off my 1ZZ earlier this year. It looked clean to me. 🤷‍♂️ Then again, I followed the manufacturer's recommended interval, not the interval displayed on some full synthetic oil jug.

Toyota engineered this era of motors to run on pure Dino oil at 6mo/5k intervals. Even using the modern synthetic blend oils available today is pampering these motors.

I guess someone should tell The Car Care Nut he is missing a huge opportunity by not offering and upselling oils in his shop.
 
supton said:
OCI = 5,000 * cylinders / (number_of_connecting_rods)
Click to expand...

Funny! It reminds me of the commercial where the customer orders an organic oat milk vegan latte with 2 half pumps of sugar free caramel.

And for my vehicles, 5000 it has always been. Change at 10,000, 15,000, 20,000 etc. No calculation or remembering anything. If it is a bit early or late, so be it.
 
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