Hello. I am using mobile 1 high mileage oil. I am putting about 60-70 miles a month on my Jeep but its been 18 months since I changed the oil. It was my first change since I bought my Jeep. It has been taken well care of. But how long does that synthetic oil last? Ive seen that you can go up to 10,000 miles before an oil change, but what about time? Its a 2000 with a rebuilt engine which has about 110k miles on it.

 

A sure way to tell how well your oil, and what it is lubricating, is holding up is with an oil analysis.
Lots of the people here use Blackstone.
Wix has a service for that too, I have used it, seems reasonable and reputable.
Also, a place near me I discovered later, used to be used by the local Cummins dealer until Cummins made them all go central, is these guys http://www.utilitylaboratories.com/

A good rule of thumb is whatever the manufacturer of the vehicle says, iirc light use is 6,500 miles on a 1996 XJ? Or one year, whichever comes first.

I get my Mobil 1 High Mileage 5W-30 at Walmart and it runs just under $30 for six quarts, Wix filter at O'Reilly. An oil analysis costs close to the same price as an oil change.

 

You're fine......

 

Most manuals will recommend 12 month intervals if you don't hit the mileage interval. I'm not sure I'd feel inclined to change it that often if I drove my XJ that little.

If it's got you up at night pull an oil sample as recommended above and send it in. They'll let you know if it's bad.

 

Oil collects moisture as it sits, I change mine once a year or every 5K. You can get 8-10K out of synthetic oil but I would recommend changing it once a year.