I have 140k on my 2006 xc70
Last oil change by mistake they used synthetic instead of conventional
Should I stay with the change and at what mileage between changes.
Thanks pete

I have a '98 V70 AWD (light pressure turbo) with 208 K miles and an '04 XC90 (same engine as the xc70 of that year) with about 190 K miles. I have been changing oil with synthetic just about every 5K miles since I bought them. I am the second owner of both, and I bought both with about 55K miles. While I may be overdoing it by not waiting 7500 miles between oil changes, I have not had any engine problems, and the oil looks pretty "done" when I do the changes at the 5K intervals. Granted, this is with about 75% of my driving around town on trips of fewer than 10 miles, but it does include several 400-500 mile round trips per cycle. I can't say that the reason I am avoiding trouble is due to the quicker interval, but spending a little more is worthwhile IMHO to do what I can to avoid problems.

I have a '98 V70 AWD (light pressure turbo) with 208 K miles and an '04 XC90 (same engine as the xc70 of that year) with about 190 K miles. I have been changing oil with synthetic just about every 5K miles since I bought them. I am the second owner of both, and I bought both with about 55K miles. While I may be overdoing it by not waiting 7500 miles between oil changes, I have not had any engine problems, and the oil looks pretty "done" when I do the changes at the 5K intervals. Granted, this is with about 75% of my driving around town on trips of fewer than 10 miles, but it does include several 400-500 mile round trips per cycle. I can't say that the reason I am avoiding trouble is due to the quicker interval, but spending a little more is worthwhile IMHO to do what I can to avoid problems.

One unconfirmed theory is that the synth oil can run for a super long time - 10K+ but it's the filter that can't go indefinitely and needs the reasonably conservative interval
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Farewell 'black manta' ('97 855na 256K) Hello 'rocket sled' ('06 V70R 136K)

+1

That is why I try to change my synthetic oil and filter at 6-7k intervals. If I changed the filter only at 5-7k intervals then I believe you could run the oil to 10k. The filter is the key.

BTW - Have you seen that one of the oil companies (forget which one) now sells a synthetic oil that supposedly only needs to be changed once a year regardless of mileage... Now that's crazy!!

Stick with the synthetic. You can pretty much double your oil change interval so in the long run it is actually cheaper than conventional! What is your oil change interval now?

It is best to use synthetic in your engine anyway as it should increase its working life and help prevent a clogged PCV system and oil leaks.

Synth oil, absolutely. Stick to current interval for next change or two, and then up to 7500 mi
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Farewell 'black manta' ('97 850) Hello 'rocket sled' ('06 V70R)

There's a caveat bandied about regarding changing from conventional to synthetic oil.
It recommends diligently checking your oil level after the switch. "The engine might drink a bit of synth. oil as the rings adjust to it", goes the tale.

No science ever offered and I check my oil frequently anyway so it wouldn't really impact my world.

Turbocharged? Use Mobil1 0W-40 or Castrol 0W-30 both European Formula as they are A3,B3 oils.

Of course there are other oils which meet the spec.

It is a good idea to check your oil frequently when you make changes until you get some history.

My son-in-law is a Subaru tech, and they have had to do an oil burning check on new cars with extended oil changes - he has had to re-ring at least a dozen new cars.

Please ask him at what mileages these ring jobs need be done on NEW CARS.
Can I just add your comment to my arguments-against-extended-oil-change-intervals library?

Back in the 'good old days', the engine oil was changed at the first 500 miles. A break in period that is no longer followed. A lot of metal gets honed in that initial period, regardless of oil formulation.

The aluminum block engines are no different, just 'softer' metal. I would never wait 7-12,000 miles for my first oil change. I would always use synthetic, it is far superior to conventional motor oil.

As to Subaru, a 're-ring' must be associated with the aluminum alloy they use for cylinder liners. I doubt that oil viscosity would make a difference. Or, some owners break in their engines with cruise control always on - a steady rpm is bad for new engines.
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Keeping it running is better than buying new