I have been thinking on and off about this for quite awhile now. Under ideal conditions, longer OCIs are probably a good thing. But what about the not so ideal conditions?
For example, suppose a normally driven car has a fuel injector that is leaking just enough to where fuel is diluting the oil enough to slightly compromise it and therefore cause engine wear (the injector not being bad enough to trigger an error code). Now running an oil 15K or longer, I can see how the wear would become worse because the owner has the impression the oil is fine for 15K, etc. The injector has more time to get fuel into the oil and would have more time to weaken the oil.
Imagine the engine finally dies and the owner thinks, "Wait a minute. The oil manufacture will warranty this as I registered my vehicle on their website and I have all of my oil change receipts." So they go through the process and the oil manufacturer runs an UOA and finds the fuel dilution. I would imagine they would say something like, "Sorry. You had a bad fuel injector. Your vehicle manufacturer will have to warranty it. Oh. You are outside of the original warranty? Sorry."
Now the same example with an OCI of 10K or less, isn't it a good thing that the oil is getting freshened up more often? The fuel dilution is less as there is a shorter time between oil changes.
Therefore, I would think longer OCIs can potentially be a bad thing if conditions are not ideal. And not everyone feels that they need to send an oil sample in during each oil change to get it analyzed.
For example, suppose a normally driven car has a fuel injector that is leaking just enough to where fuel is diluting the oil enough to slightly compromise it and therefore cause engine wear (the injector not being bad enough to trigger an error code). Now running an oil 15K or longer, I can see how the wear would become worse because the owner has the impression the oil is fine for 15K, etc. The injector has more time to get fuel into the oil and would have more time to weaken the oil.
Imagine the engine finally dies and the owner thinks, "Wait a minute. The oil manufacture will warranty this as I registered my vehicle on their website and I have all of my oil change receipts." So they go through the process and the oil manufacturer runs an UOA and finds the fuel dilution. I would imagine they would say something like, "Sorry. You had a bad fuel injector. Your vehicle manufacturer will have to warranty it. Oh. You are outside of the original warranty? Sorry."
Now the same example with an OCI of 10K or less, isn't it a good thing that the oil is getting freshened up more often? The fuel dilution is less as there is a shorter time between oil changes.
Therefore, I would think longer OCIs can potentially be a bad thing if conditions are not ideal. And not everyone feels that they need to send an oil sample in during each oil change to get it analyzed.