XJ40 OIL change question

I am planning to replace engine oil. Last oil change was done in september 2022 from the previous owner and the car did 12.000 km since then. As i can see from the service manual , is suggested an oil change every 12000 km or 6 months.
I think i will drive no more that 5000 km years, so i am asking which oil change plan is suggested, as the car is now not daily used but is used as classic car. My idea is to use a semi synthetic oil 10w40 and change every year . what do you think?

Ignore 6 month time frame, just go by mileage or do it once a year if you feel like it. Our engines have huge sumps and can go longer than 6 months without changing oil. Synthetic is more prone to leaking, I use GTX 20-50 BTW.

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When I worked at the dealer a few decades ago, some MY cars came with ‘included maintenance’ up to 40,000 miles.

All the cars from the late 1990s (V8 cars) recommended 10K mile intervals.

We serviced the cars every 10K miles OR 12 months. (which ever came first)

The service recommendations for earlier North American cars (L6 engine or V12) was 7.5K miles.

Service sheet we filled out for records.

S_18_4.PDF (23.6 KB)

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I just changed the oil yesterday (June 4). OEM filter and drain plug washer, 10W30 Quaker State full synthetic oil. I do it once a year, typically in May because I want fresh oil in the engine before the summer heat comes. I drive around 5000 miles (8000 Km) a year.

Yearly with 10W40 sounds great. I would not wait much longer because acidity can build up and eats the bearings especially on little used cars with infrequent oil changes.

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In my Southern California climate 20w-50 is the correct oil for AJ-6 in the XJ-40. 10W-40 for x300 with the AJ-16 engine. Cars after the AJ-16 are completely different.

AJ-6, particularly the earlier ones, don’t like thin oil. We serviced lots of those cars with lots of miles and that worked well.

Personally, I ran 0W-50 synthetic in my 1991 XJ6 as it had to work in below 0F and 115F since I drove a lot of my cars back and forth from So California to my house in Park City, Utah plus lots of winter trips to further Northern Rockies.

I change mine annually regardless of mileage but for the last few years I’ve never covered more than 5000 miles in a year. I’ve always used Castrol, 20W 50 if I can get it or 10W 40 when I can’t.
Just take care removing the sump plug, they have been known to strip the alloy threads in some cases. I don’t know why that is, maybe they have been overtightened in the past, but I also read somewhere it was a reaction between the steel plug and the alloy sump that causes it. I use a vacuum oil extractor and do the entire job including changing the filter from above without having to get underneath the car so I never disturb the sump plug.