Does adding oil mid-interval extend the change?

[WobblyElvis]

My car has gradually started to burn and leak oil over the past 6.5 years I have owned it. Used Oil Analysis over the years indicated the lowest ppm of wear metals when 3 litres of oil was added over a 15,000 mile oil change. Of course you can't make a conclusion on just this one experience but it does appear to me that adding oil to an engine during the OCI does extend the life of the oil. TBN was also relatively high.

 

[kschachn]

Originally Posted By: WobblyElvis
My car has gradually started to burn and leak oil over the past 6.5 years I have owned it. Used Oil Analysis over the years indicated the lowest ppm of wear metals when 3 litres of oil was added over a 15,000 mile oil change. Of course you can't make a conclusion on just this one experience but it does appear to me that adding oil to an engine during the OCI does extend the life of the oil. TBN was also relatively high.

Well it certainly dilutes the wear metal measurement, that's for certain. I don't know how you could make any correlation to a reduction in actual wear however.

 

[Ikken]

In the EU, most new (pro 2005) user manuals state that the change interval can be set for 20,000 miles or 30,000 kilometres for diesel and petrol vehicles as well. With the sidenote (obviously in size 5 Arial) that short trips, commutes and heavy loads might even decrease this interval to 5000 miles or 8000 kilometres. The best part is that if you roll in to a dealership they usually do not recommend changing the oil unless you are closing to these distances. I am just stating my own experiences, nothing more. 15000 miles sounds like a stretch and might be okay taking long trips, but I would not have the nerves to do it, kudos for that.
My personal opinion is, that the manufacturers push the oil change intervals just to become more clean doing less oil changes thus being environmentally friendly. The innovation is in the oil already with the low viscosity oils doing around 3.0 HTHS, but anybody who says can create an oil that goes for 30k miles with no issues are speaking nonsense. In the 90's japanese engineers started recommending lower performance oils with ridiculous OCIs - 5000kms or 3000miles running 10w/15w-40 dino SI-SH.
It's hard to find what's optimal, as always.

 

[JLTD]

Originally Posted By: kschachn
Originally Posted By: WobblyElvis
My car has gradually started to burn and leak oil over the past 6.5 years I have owned it. Used Oil Analysis over the years indicated the lowest ppm of wear metals when 3 litres of oil was added over a 15,000 mile oil change. Of course you can't make a conclusion on just this one experience but it does appear to me that adding oil to an engine during the OCI does extend the life of the oil. TBN was also relatively high.

Well it certainly dilutes the wear metal measurement, that's for certain. I don't know how you could make any correlation to a reduction in actual wear however.


Good point about dilution of metals...perhaps a sample should be taken before and after adding to create some data

And although it would skew the UOA's ppm results, it would actually help the current fill last longer...both in TBN and condemnation levels of wear metals.