Summary. This article was submitted by Sherman J. of Maryland and offers a general assessment of motor oils and engine care.
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Any oil that meets or exceeds the mfr’s requirements for weight and API grade (“SJ”, “SH”, etc) is fine. These days it seems most cars fall apart before the engine blows up. All the oil mfrs try to differentiate themselves, and there may be slight differences, but the main thing is that the oil has the proper weight and service grade. Back when we still shopped at Wal-Mart, I’d buy their house brand synthetic oil. It was cheap (for synthetic) — $2.97 vs. maybe $5 or so for the name brand oils. I figured it had to be made by one of the major oil companies, and it had the proper ratings.
I’ve always used synthetic, but primarily as a little added insurance since I use the longer “regular service” 7,500 mile oil change intervals (instead of 3,750 or 5K). I didn’t exactly baby my cars when going back and forth to work, but they’ve held up well. The Subaru is actually modified and putting out quite a bit more hp and torque than stock — 285/285 vs. (I can’t remember exactly), maybe 224/218. This puts more strain on the engine. I had the oil from the Subaru tested twice — once with about 5K miles on it, the second time with around 7,500 miles. Both times the lab (Blackstone) said it was fine. In fact, they said I could run it for a couple thousand miles longer but I figured I’d stick with 7,500. The Nissan has about 250,000 miles and the Subaru close to 200K. Neither burn very much oil. I may have to add 1/2 quart between changes.
A lot of people are still under the misconception that they must change their car’s oil every 3K miles. The oil change places like Jiffy Lube seem to support this misconception. Last I noticed they were still pushing the 3K mile oil changes. I’m not aware of any auto mfr that has less than a 3,750 mile interval, and that’s for “severe service” — police, taxi, towing, lots of short trips (engine never gets warm), lots of dirt roads/dust, etc. The “severe” oil change interval for our RAV4 is 5,000 miles (normal is 7,500). Your car might qualify for the shorter interval (whatever is in your owner’s manual) if you do a lot of driving in town. If it’s mostly road trips then go with the longer interval. Any oil that meets the mfr’s specs is fine. I definitely would not use synthetic if you’re changing it every 3 or 4K miles — it seems like a waste.
It’s worth mentioning that using the longer (7,500+ mile) service interval saves: resources (oil, and steel for the oil filter); time (whether you do it yourself or go to a shop); and money — less oil, fewer filters, and less in labor charges for those that go to a shop. Of course, people should always use the shorter interval if there’s any question as to whether their vehicle falls in that category.
Some vehicles (like Mercedes) have an ECU (engine control unit) in some of their vehicles (maybe all now?) that keeps track of how the vehicle is driven and recommends oil changes based on operating conditions. The high end of the oil change interval range is from 10,000 to 20,000 miles. That is with synthetic oil and is under ideal driving conditions — decent temperature, no short trips, mostly highway miles (very little idling and stop-and-go).