Quote:
Originally Posted by cn90
- Even the car gurus (Larry Carley et al) say most people belong to the "severe service cycle" and this is what they say:
* Standard oil: every 3K-4K
* Synthetic oil: every 5K-6K
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If that is his generic recommendation (and it sounds like he would apply it to a wide range of vehicles) then how does he modify it based on sump capacity?
With heavy duty industrial engines, our customers often wanted extended oil change intervals. The way to do that most effectively was to double the sump capacity; that way the manufacturer supported a doubling of the oil change interval. More fluids could hold more contaminants in suspension, and the additives lasted longer. BMW vehicles have oil sumps that are generally twice the size of many other vehicles (8 litres vs 4, for example). That is part of the longer change interval design spec.
What I am not clear on is why the recommendation would be to extend the interval with synthetic fluids. There are too many other variables in play, and it sounds a little like a synthetic oil commercial. One of the variables is filter life; if you get a longer oil change interval without using an appropriate filter you may need to do an extra filter change at half the oil change interval.
When we were extending oil change intervals beyond the manufacturer's spec due to special service requirements (ie engines in remote areas) we would try to establish whether we could go 1.2 or 1.5 or 2 times the scheduled interval. We did a lot of extra oil sampling, typically 5 or ten extra samples on each engine. And don't start at the scheduled interval, you need a baseline sample of new oil, and then throughout the test period, as you want to see where TBN is dropping off, and not just get a figure at the scheduled interval. For most customers, it was more trouble than they wanted, but if you were flying crews in to do services then it could pay. Those engines were running continuously, in either power generation or pumping applications, with scheduled overhauls at 15k, 30k, or 60k hours depending on the engine series, load factors, and fuel source.