oil life.. Additive depletion or contamination?

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What typically kills motor oil over time, contamination or additive depletion?

Do most of the additives get used up or just some? Do some never change over time?
 
Depends on the engine...

Worn engine with blow-by, it is thickening of oil and TBN depletion due to trying to neutralize acid formation.

New engine, it is either shear, or AW depletion. But the later can be tricky because AW compounds form over time and are unique the engine. So as long as the TBN remains tolerable and the oil is not thickening, it can go a long ways. We have a member here with 62,000 miles on original fill of Amsoil with by-pass filtration and top-ups when he changes filters.

Alcohol and GDI engines, or old carb'd engines out of spec can have fuel dilution and that is a real issue ...
 
If syn oil and by pass filters are so good why do they need to have oil added to them. My 200,000 mile Edge that has lived on dino 15w-40 diesel oil still doesn't have to have anything added to it in 6,000 oil changes.
 
Originally Posted By: rideahorse
If syn oil and by pass filters are so good why do they need to have oil added to them. My 200,000 mile Edge that has lived on dino 15w-40 diesel oil still doesn't have to have anything added to it in 6,000 oil changes.


Oil top ups WHEN the filters are changed!

I'd love to try a bypass filtration system myself but don't do enough mileage on my own cars and my Focus is a company car.
 
Originally Posted By: rideahorse
If syn oil and by pass filters are so good why do they need to have oil added to them. My 200,000 mile Edge that has lived on dino 15w-40 diesel oil still doesn't have to have anything added to it in 6,000 oil changes.


My three Ford Duratech I-4 engines that I have owned in the last 12 years, perhaps like yours, have had 0-20 M1 in them for 10K OCIs and use no oil at all. Last time I checked I have put over 400K with 20wt synthetic oil on them.
 
My Fusion 2.5 (essentially same as tig's) has gone nearly 100k on 6 oil changes under my ownership... and I haven't had to add an ounce of oil during any OCI. 0W20/5W20 PP and PUP during this time. So there's two major oil companies and three formulations that work just fine.
 
Originally Posted By: rideahorse
If syn oil and by pass filters are so good why do they need to have oil added to them. My 200,000 mile Edge that has lived on dino 15w-40 diesel oil still doesn't have to have anything added to it in 6,000 oil changes.


Because they change filter media and that means a qt of make-up oil. They also sample for UOA's, so that needs some make-up oil too.
 
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