I would like to publish Ted from Dixie Synthetics formula for oil change intervals. I think this formula has merit and better than mileage or time alone can ever be in managing oil changes.
The reason to publish this formula? We just finished an evaluation of oci's for a document delivery company and this formula worked over a two year period better any other scheme we know of. We did not get to the time part of any formula because these vehicles were doing sometimes 500 to 650 miles a day and the least mileage vehicles were still over 250 miles a day. We had some vehicles with an OLM and we followed them for one group.
A side note on OLM's. They work. I know that they work but if you keep a vehicle the time beyond the warranty period and performance is not known. In other words if you keep your vehicles you might want to consider a more aggressive schedule.
This testing is like the Las Vegas taxi tests, that is they are not completely valid for the average owner/driver. You're shorter runs might be a bit harder on your vehicle if considering odometer reading and just the opposite if considering the calendar.
If synthetic oil was better for protecting against failures then it did and we did not see the failures so the process defeated itself.
Several synthetics were used all did well enough that one could not detect an differences. One synthetic did produce slightly better numbers, Amsoil 10w30 ACD. This oil was also used in some older specialty vehicles that are kept much longer. Vehicles in this category would be utility vans/truck with special bodies and /or special equipment built into the vehicle. An example. An armored truck. These are worth rehabing.
A synthetic blend that stood out was Motorcraft 5w-20 and in all cases now where a 5w-20 is called for the choice is Motorcraft, not a full synthetic. If the vehicle is a specialty vehicle that calls for 5w-20 it will be switched to ACD after the warranty period. If a 5w30 is called for then it's ACD. No extended warranties are used. With the maintenance facilities available it has been determined that extended warranties are not a good investment.
Formula-------------------------------------------
OCI(miles) = (C*)(aver.mpg)(sump-qts)(cubic inches/Hp**)
Where C* is an empirically derived constant, that depends on both the quality of the basestock and the robustness of the add pack.
** For turbo diesels, substitute ft-lbs of torque for Hp, as this is a better measure of turbodiesel output. If you were to use Hp, you'd over predict a reasonable drain interval.
As for the C* values, most of the work I've done has been with Amsoil, where I back fitted a series of oil analysis results and varied the C* until I was getting reasonable OCI's for engines of varying size and output. However as a first cut, I'd say a C* of 50 for a petroleum oil and a C* of 80 for an average quality, off the shelf synlube should be about right. The top tier, PAO/Ester synthetics (Amsoil,GC,Redline) are assigned a C* of 125. The Series 2000/3000 oils probably rate a C* of 150, i.e. they do last a bit longer than the regular Amsoil 5w30 or 10w30.
As a final note, the units in the above formula do not cancel to yield miles when you multiply them through. So just ignore that and use the numerical data and forget about the units. I know this bothers some engineers , and I suppose you could assign some funky units to the C* value to get everything to come out right, but I haven't done that.
Ted
Dixie Synthetics
The reason to publish this formula? We just finished an evaluation of oci's for a document delivery company and this formula worked over a two year period better any other scheme we know of. We did not get to the time part of any formula because these vehicles were doing sometimes 500 to 650 miles a day and the least mileage vehicles were still over 250 miles a day. We had some vehicles with an OLM and we followed them for one group.
A side note on OLM's. They work. I know that they work but if you keep a vehicle the time beyond the warranty period and performance is not known. In other words if you keep your vehicles you might want to consider a more aggressive schedule.
This testing is like the Las Vegas taxi tests, that is they are not completely valid for the average owner/driver. You're shorter runs might be a bit harder on your vehicle if considering odometer reading and just the opposite if considering the calendar.
If synthetic oil was better for protecting against failures then it did and we did not see the failures so the process defeated itself.
Several synthetics were used all did well enough that one could not detect an differences. One synthetic did produce slightly better numbers, Amsoil 10w30 ACD. This oil was also used in some older specialty vehicles that are kept much longer. Vehicles in this category would be utility vans/truck with special bodies and /or special equipment built into the vehicle. An example. An armored truck. These are worth rehabing.
A synthetic blend that stood out was Motorcraft 5w-20 and in all cases now where a 5w-20 is called for the choice is Motorcraft, not a full synthetic. If the vehicle is a specialty vehicle that calls for 5w-20 it will be switched to ACD after the warranty period. If a 5w30 is called for then it's ACD. No extended warranties are used. With the maintenance facilities available it has been determined that extended warranties are not a good investment.
Formula-------------------------------------------
OCI(miles) = (C*)(aver.mpg)(sump-qts)(cubic inches/Hp**)
Where C* is an empirically derived constant, that depends on both the quality of the basestock and the robustness of the add pack.
** For turbo diesels, substitute ft-lbs of torque for Hp, as this is a better measure of turbodiesel output. If you were to use Hp, you'd over predict a reasonable drain interval.
As for the C* values, most of the work I've done has been with Amsoil, where I back fitted a series of oil analysis results and varied the C* until I was getting reasonable OCI's for engines of varying size and output. However as a first cut, I'd say a C* of 50 for a petroleum oil and a C* of 80 for an average quality, off the shelf synlube should be about right. The top tier, PAO/Ester synthetics (Amsoil,GC,Redline) are assigned a C* of 125. The Series 2000/3000 oils probably rate a C* of 150, i.e. they do last a bit longer than the regular Amsoil 5w30 or 10w30.
As a final note, the units in the above formula do not cancel to yield miles when you multiply them through. So just ignore that and use the numerical data and forget about the units. I know this bothers some engineers , and I suppose you could assign some funky units to the C* value to get everything to come out right, but I haven't done that.
Ted
Dixie Synthetics
