The first oil change interval is coming up that I haven't met via mileage, but instead, time. Is the overall thesis behind changing oil after a time interval just water accumulation causing corrosion internally?

 

How much mileage are we talking here? I’m not sure how much truth there is to water accumulation if you are driving it regularly (if infrequently) as long as you are allowing it to get up to temperature. A big reason to regularly drive your truck for a little while is to let the fluids get up to temperature and boil off the moisture so it shouldn’t be accumulating. Ultimately these engines like frequent oil changes because they are old and dirty and getting some fresh oil in there is always a good idea. Plus there is a benefit to keeping to a schedule.

 

I have never changed my oil based on the calendar, mileage only. However I do drive each vehicle somewhat regularly, if nothing else a run up to temp at least once a month if not more. This is more the result of a lifestyle approach than a strict adherence to any schedule. While I'm certainly not an authority on the topic, I'm old enough to have a more than a couple decades of automotive maintenance under my belt.

 

I do based on mileage and time. It is 2K miles or 6 months. Whatever comes first.

 

Depends on how you store the car as well, if you keep it in a dry, climate controlled garage and ran the car for a while beforehand it can sit for a long time. If you store it outside with weather and temp changes it's more risky, generally speaking even if it just sits indoors you should change oil at least once a year but really the engine should be at least hand rotated every few weeks.

These engines are fairly simple with relatively high amounts of oil capacity vs oiling demands so if a high quality oil is used you may be able to go past 5k miles without risks. Modern stuff I blanket recommend 5k or less with a full syn to avoid any chance of wear/issues with how demanding modern engines can be. The rover engine could likely go 10k though....

 

Good perspective, thanks. We got a Tesla for a daily driver in May, so the Disco went from 15-20k miles/year to, well, it’s been six months since the last oil change and I’ve only driven about 2500 miles. Every drive though is at least an hour, plenty of time to get up to temp.

 

With that info I'd still just stick to the 5k change or whatever your mileage interval is. I just had to switch to royal purple (whatever their diesel 15-40 is called) as the rotella t6 is basically impossible to find near me and I couldn't put it off any longer.

 

Change it ever 5K.

 

There was a study reported here or somewhere else a few years ago addressing this question. The bottom line is that analysis of oil that was in a crankcase for extended periods (e.g. 2-3 years) showed no statistically significant degradation beyond what would be expected from the miles driven. In other words, ignore the calendar.

The last time I changed the oil in my truck was October '19. I've put only 2500 miles on it since then. At this pace I'll next be changing the oil in in June 2025,

 

It depends on driving habits. Oil degrades with number and length of heat cycles, temperature and not only miles. If you do only long distance driving then I would go by mileage. If you are going only around town, I would change it by calendar. Too short drive cycles can lead to accumulation of water. The hotter the oil gets, the faster it degrades.