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Q: Type of oil and when to change

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My son's Jeep Liberty Jet has had oil changes by the dealer every 3,000 since he bought it in 2012. The service book says the car oil and filter should be changed every 8000 miles. The oil being used is standard 5W-20 MS-6395, NOT synthetic or part synthetic. The dealership says the car is not designed to change the oil back and forth to a synthetic, and I saw on your website the recommendation to change synthetic oil is every 6000. Please explain: 1.Why should I keep changing regular oil every 3000 for this car? 2. Is it bad for my car to change over to synthetic oil, and why? 3. Is my car too old to change to synthetic, and why? Thanks!

My car has 52300 miles.
My car has an automatic transmission.

Oil change intervals on your vehicle are determined by the vehicle’s engine oil change monitoring system. A message on your instrument panel will alert you when it is necessary to change the oil. The change interval is based on a computer algorithm and is "duty cycle based". Consequently, the oil change interval is not fixed and will vary depending on personal driving style and drivings conditions. For example, lots of short trips will necessitate a more frequent oil change than if your driving mileage is accumulated under continuous highway driving. An engine computer keeps track of all the required data, processes the data, and then the car’s messaging system lets you know when to change the oil. With some minor caveats, as stated below, synthetic oil can be used at any time and you can switch back and forth between conventional oil and synthetics at any time. Although existing leaks may potentially leak at a somewhat greater rate when using synthetic oils versus purely mineral based (aka, "conventional" oil), the added leakage, if any, is meaningless in most seal locations and in most circumstances. The potential for a leak is due to the smaller size of the molecules in synthetic versus conventional oils. However, synthetic oil cannot possibly cause or otherwise mechanically enlarge a leak. In any event, any "distinction" in leak rate is meaningless simply because if you put synthetic oil in a car and you can see a leak from a seal, that seal was most decidedly leaking anyway with regular oil and so would have to be repaired regardless of the oil "type" you are using.


In your specific case, with a relatively newer car and low miles on the engine, this possibility of a leak probably does not exist at least for a while, although you are getting close to the time frame when just due to rubber aging (over time, not mileage related), leaks will start developing anyway. The bottom line is you can and should use synthetic oil in your circumstances due to its huge advantages in physical properties and potential to lengthen the service life of your engine and even seemingly unrelated parts such as oxygen sensors and the catalytic converter (synthetics don’t have the sulfur and other elemental contaminants that mineral oil has). Full synthetics will be less subject to degradation and evaporation during the oil service interval, too. I would recommend you use "100% synthetic oil". If it were my car I would use the most expensive, highest rated synthetic oil I could find. Changing your oil removes dirt and contaminants and newer cars with all sort of oil actuated mechanisms, such as variable valve timing, need very clean oil. YourMechanic offers oil and filter changes during mobile visits right to your location and you should certainly avail yourself of that service as the cost is lower and the service is much more personalized than at a shop or dealer. If you have additional concerns, don’t hesitate to re-contact YourMechanic.

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