Fuel usage vs mileage in determining OCI?

[opposite_locker]

My '08 Dodge sees ALOT of miles (4-5k per month), but it does also spend quite a bit of time idling around our orchards. On average, the truck idles about 20hrs per month, and up to 40 hrs in the summer months - usually with the AC on and an ambient temp of 90-105 degrees.

The truck only averages about 13 mpg with my driving habits, so with the current OCI (German Castrol at 10k with filter change/topoff at 5k), the engine will be burning more than 750 gallons of gas between oil changes.

Since oil pollutants are generally created as a result of combustion, then is a v8 engine that has burned twice the amount of fuel as a smaller engine over the same distance likely to have less TBN remaining in the oil?

 

[ekpolk]

Of course, "it depends..."

Generally though, I think you're on the right track. Another member recently posted that Ford considers one hour of idling to be the equivalent of 33 miles driving. I don't know the actual source of the info, but that would seem about right to me.

 

[jorton]

Originally Posted By: opposite_locker
Since oil pollutants are generally created as a result of combustion, then is a v8 engine that has burned twice the amount of fuel as a smaller engine over the same distance likely to have less TBN remaining in the oil?


That's what happened in this Police Interceptor:

http://www.bobistheoilguy.com/forums/ubb...rue#Post1441081

 

[JHZR2]

See here:

http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Board=1&Number=1502602

 

[StevieC]

Originally Posted By: opposite_locker
My '08 Dodge sees ALOT of miles (4-5k per month), but it does also spend quite a bit of time idling around our orchards. On average, the truck idles about 20hrs per month, and up to 40 hrs in the summer months - usually with the AC on and an ambient temp of 90-105 degrees.

The truck only averages about 13 mpg with my driving habits, so with the current OCI (German Castrol at 10k with filter change/topoff at 5k), the engine will be burning more than 750 gallons of gas between oil changes.

Since oil pollutants are generally created as a result of combustion, then is a v8 engine that has burned twice the amount of fuel as a smaller engine over the same distance likely to have less TBN remaining in the oil?


If you are idling that much I would knock your OCI down to 8K miles and change the filter/oil at that time.

If the 1 hour of idling is in fact equivalent to 33 miles then that means you are adding 660 miles to your original 10K OCI and that's a bit much IMO.

8K miles with 660 miles worth of idling would be better IMO using a high quality synthetic like you are using.

If you want to continue doing 10K OCI's with a top off/filter change at 5K I would do a UOA to verify that the TBN hasn't gone too low and the TAN/Fuel dilution is staying at acceptable levels. If they are then continue on as you are doing...

 

[Quattro Pete]

Originally Posted By: opposite_locker
The truck only averages about 13 mpg with my driving habits, so with the current OCI (German Castrol at 10k with filter change/topoff at 5k), the engine will be burning more than 750 gallons of gas between oil changes.

The OCI in my car (3-liter I6 with 7qt sump) is based on 627 gallons of fuel consumed. On average, I get about 25 mpg, so that would mean 15,600 miles. However, I can't force myself to wait that long. I typically change it before 8k miles or 1 year, whichever comes first, although the UOA showed the oil was still suitable for continued service and the TBN was around 6, so technically I could go longer. I just get an itch to do it early.

In your case, I'd probably do a UOA to see how this oil is holding up and adjust the OCI based on that.

 

[zoomzoom]

given that you get 13mpg you use aprox 4 gallons per hour of engine operation/driving at 55mph

now when you idle your engine speed is about 700 rpm which is 1/3 of the engine speed required to do 55 mph and as a consequence you use at most 1/3 of the fuel while you idle

so each hour spent at idle would use aprox 1.3 gallons of gas or could count as 17 miles driven toward your oci

I think GC should be able to handle 10K + 680miles(summer idle time) without any trouble since it is a A3 rated long drain oil.

 

[djlinux64]

The amount of fuel you use at idle cannot be compared to the amount you use while moving due to the difference in engine load. Your premise is incorrect and argument invalid.

 

[Quattro Pete]

Originally Posted By: zoomzoom
now when you idle your engine speed is about 700 rpm which is 1/3 of the engine speed required to do 55 mph

I would expect a large 4.7l engine to run at less than 2100 rpm @ 55 mph.

Quote:
you use at most 1/3 of the fuel while you idle

Yeah, I would assume a lot less at idle. FYI, the OBC in my car shows about 7-8 liters/hour when at 55mph, but only about 1 liter/hour when at idle.

 

[Doug Hillary]

Hi,
opposite_locker - Yes, fuel consumed is the "purest" way of determining an OCI

 

[FZ1]

In a general sense ,yes.

 

[opposite_locker]

In that case, I will likely shorten my summer OCI's down to 7500 miles and stay with 10k in the fall/winter/spring.