When An Extended Drain Isnt an Extended Drain.

[Gene K]

When an extended drain isnt an extended drain. For those that havnt heard of this before I wanted to introduce an alternative method of picking an intial OCI (Assuming you dont have a special needs engine). Many of the large engine manufacturers in this world have said that the single most important issue for oil longevity is not mileage but fuel use. Im going to try applying this strategy to different light vehicles.

I will use a formula of: MPG x Oil capacity x Relative Strength Of the Lubricant. (Mobil 1 Synthetic having a rating of 100)

1974 Chevy Truck (12 mpg average)
400 V8 (5 Qt)
2bbl Carb
Conventional Group I (Rating 50)
Mobil 1 Full Synthetic (Rating 100)
12 x 5 x 50 = 3,000 mile with GI Conventional (Sometimes its not a myth)
12 x 5 x 100 = 6,000 mile with Mobil 1 Synthetic

2011 MUSTANG GT (22 mpg average)
5.0 V-8 (8 Qt)
EFI
Motorcraft Synthetic Blend GII/GIII (Rating 70)
Mobil 1 Full Synthetic (Rating 100)
22 x 8 x 70 = 12,320 miles with MC SB.
22 x 8 x 100 = 17,600 miles with M1 Synthetic.

I dont think most would consider a 3,000 mile OCI extended in the truck. Yet many of us would worry about the 10,000 mile max change interval Ford specs on the new Mustang, As you can see it may actually be the least stressed of the pair.

Disclaimer: For illustration purposes only. Adopt strategy at your own risk!

Just something to think about.

 

[rclint]

I agree with you on the fuel usage, however when taking into account the older engines somehow for real world purpose it needs to be kept in mind how much fuel got into the oil from the carburetors. Just by having fuel injection alone maybe double the OCI not counting what you showed above, then take into account the outstanding quality of oil today compared to years past I'm surprised really we are stuck with the stuck with the seemingly modest 10k OCI's

 

[Gene K]

Yes fuel dilution can be an issue. I decided at the last minute not to get into that as I felt it was better to focus on the principle I was trying to convey.

 

[buster]

Gene, did you get this formula from Tooslick?

 

[buster]

The actual formula is:

OCI = (C*)(sump-qts)(mpg)(cubic inches/Hp^)

^ Note: For turbodiesels, use ft-lbs of torque instead of Hp.

C*:

Dino oil, 60
Average Syn, 90
Long Drain Syn, 125
Amsoil SSO, 150

 

[SpitfireS]

This only works with a list of oils and their relative strenghts.
IOW: it's all open for (lots of!) debate.

Does the formula also works the other way?
To "calculate" what oil to use?

MY'00 Honda S2000 - average mpg 26
5 quarts
Multipoint fuel injection
Wanted OCI = 25000km (=15537 miles)
This formula shows I need an oil with a relative strenght of 119.
Would SSO be strong enough for the job?

With my MY'00 engine I had a LOT more fuel dilution than with the MY'05 engine, btw.
So I guess one needs to do a UOA first to see IF one has a fuel dilution problem.

 

[Gene K]

Originally Posted By: buster
Gene, did you get this formula from Tooslick?


No, Its kind of loosely based on the formula used by engine manufacturers like CAT. In their formulas hp is never considered. A 350 bhp and a 600 bhp use the same interval.

If you think about it average power the engine is run at would be included in mpg. The higher the average load the lower the mpg. However all these engines are the same size so that would mean average power delivered per displacement would drop as mpg climbed.

After thinking about it I see where power density would need to be figured in as well. That is a worthwhile addition.

My main point was to get people thinking outside the constraints of simple fixed mileage.

 

[Gene K]

Originally Posted By: SpitfireS
This only works with a list of oils and their relative strenghts.
IOW: it's all open for (lots of!) debate.

Does the formula also works the other way?
To "calculate" what oil to use?

MY'00 Honda S2000 - average mpg 26
5 quarts
Multipoint fuel injection
Wanted OCI = 25000km (=15537 miles)
This formula shows I need an oil with a relative strenght of 119.
Would SSO be strong enough for the job?

With my MY'00 engine I had a LOT more fuel dilution than with the MY'05 engine, btw.
So I guess one needs to do a UOA first to see IF one has a fuel dilution problem.

Not sure if you are referring to my formula or TooSlick's (Posted by Buster).

Thats why I noted an engine without special needs. As I stated in my previous post Im not saying that the little formula Im using is 100% accurate just trying to get people thinking. I see to many people that would do 3,000 mile OCI or 5000 mile OCI on both the examples I used when they are in no way equivalent.