20 mins away? You live in Los Angeles or Louisiana???!!!
I've only changed it once since I got her (mid Jan) but looks like the prior owner did it every 5,000 miles, synthetic at the dealer...

 

20 mins, yes! I live my L.A rules by the movie Clueless!

 

Never having seen anything to change my mind, I go by the Army's oil testing at Aberdeen Proving Grounds about thirty years ago now. No dino oil made 3000 miles before a loss of 30% lubricity and all synthetics were still going strong at 12000 miles. No measurable differences in wear with any synthetic oil. Only Valvoline dino oil made it to 3000 before excessive breakdown.
I change oil in everything in October regardless of mileage with whatever synthetic is on sale. Only oil related problem I ever had was a gasket failure on a filter, messy that.

 

Same to you.

You have asked an unanswerable question. The OEM oil change interval is based upon the use of non-synthetic oil. This interval has proven to be appropriate as we now know with an aging fleet where lubrication issues are virtually unheard of.

You have chosen to use a different type of oil that, according to many, should allow an extended change interval ie exceeding the OEM's spec for non synthetics.

Without extensive testing over hundred of thousands of miles on dozens if not hundreds of cars, how would anyone know what the interval using synthetics would be?

 

I think if you change your oil at 3k miles it's just a waste of money. Oil now days last way longer than 3k. the new mobil one oil lasts 20k MILES!!!!

 

Even though I use synthetic oil for my own reasons, it cannot be denied that what you call dino oil is much different that the oil tested thirty years ago. There were also very good oils then. It is simply that industry standards raised the bar and new chemical technology became available.

Oil is a wear, contamination and heat transfer solution. Most people neglect this last part as it is very important in modern engines.

A real life example of its adequacy is my girlfriends early 2000's Japanese car. The use fits the profile of non-abusive normal service with high mileage. The engine is very good with an incredible amount of mileage by today's standards. This is using dino oil changed on schedule. The only thing that I notice is some varnishing in the top end when adjusting the valves and only moderate sludge. In my engines using synthetic, I do not get this. Mechanics who see my engine open are impressed. However, the real question is whether this is any sort of issue as the dino car has no oil pressure change from spec, bearing issues, clogged oil paths or sludge in the pan, verified during an oil pan gasket repair.

This means that when you have a vehicle spec'ed for dino oil, synthetic is really only necessary if you are doing something out of spec or abusive or to make up for a shortcoming of the original spec. In some cases a new product might be missing something that the engine needs as is the case with rotary engines or older pre emissions engines (zinc, etc.).

Some cars do specify synthetics, however it is interesting to note that GM reversed itself including with the Corvette. The more recent products no longer specify synthetic only. It is a cost savings measure for them, but still makes the point.

I will grant knowing engineers personally that sometimes manufacturers do things for reasons that they do not agree with. It is a big deal to limit required service to yearly or longer mileage. Add in the scourge of leasing and many manufacturers might not be as concerned about the top end of service life and are willing to make trade-offs that do not affect the first user. If you purchase something, resale is often an issue and there would be concern that future purchasers can depend upon a reasonable service life window. With leasing this is not so much of an issue even for the second user who could be another lessee or finance customer who will rollover to another model within four years. Anyone who purchases after that is a non issue from a standpoint of market perception. Us buy and keep people are a different group.

 

and I would like to add in agreement to what you just said that the nature of the collector hobby will limit mileage even for those who use these vehicles a lot. Even long road trips will not make up for a user with other regular service vehicles in most cases. With regular use vehicles the average user, actually most, is not going to keep a vehicle fifteen years or past a certain mileage. This limits the data to the outliers or fleet or specific use, usually highway, which is mostly the best kind of mileage. When testimonials from long haul users of regular vehicles is presented as proof of the synthetic oil's contribution to the high mileage great running engine, I often wonder if the same would occur using regular oil spec'ed for the vehicle.

 

Keep in mind that this same 4.2L engine was also used in the S-type and XJ series of cars, both in NA and supercharged version. These series of cars being four door saloon/sedans were more likely to have been used as year-round daily drivers (mine certainly was). Some of the most senior examples are in the 200K-300K mile range and as stated above lubrication related issues are unheard of.