OK, my 97 Xk8 with 83k on it. I have been running Mobile One Syn oil in it since we got it at 65k, now at 83k. I just changed out the oil with what seems to be a new Mobile One Syn oil product that says it is good for 15k miles. What do you think of that? As it is now we drive the car about 5-7k a year so at that rate I would do ONE oil change a year. I did two oil changes last year, and planned as many this year, one end of fall and one late spring unless we drive it more and I think I should change it. The car does see HWY time to get it up to running temp and driving at HWY speeds for a bit so it is getting its legs run out a little couple times a week.
What do you think this game plan, is it safe?

 

Pure synthetic or not, oil is petroleum. Petroleum products are hygroscopic, meaning they absorb moisture from the atmosphere. Oil + water = sludge. Add in the fat (rich) mixture an engine sees at every cold start, plus the extra blow-by (air past the piston rings) of newer engines due to low drag/low tension rings (especially with Nikasil coated cylinders) and you can see how oil contamination adds up. Typical recommendations are for an engine to see at least 45 minutes of steady, hi-speed (50 mph+) at least weekly, in order for the oil to remain at a temperature high enough for these contaminants to be 'steamed' from the oil and evacuated through the crankcase ventilation system.

For engines that see a lot of miles each year, synthetics make a bit of sense (think long-haul trucks.) For engines that don't see that kind of usage the ROI of synthetics is pretty poor. The extended oil change intervals recommended by OEMs are a marketing ploy (When buying a new car, who really thinks they're going to save money because they only need half the oil changes?) read the fine print: "Except in cases of severe Service. "What constitutes 'severe service'? Extended periods of idling, dry, dusty conditions, humid conditions, stop-and-go traffic, towing, reading the newspaper, eating dinner more than once each week... Cut the extended recommendation in half, easily. Even without the mileage it's recommended that oil, synthetic or not, (however the synthetic boys will never advertise this) be changed every six months due to petroleum's hygroscopic properties.

So, a quality, non-synthetic oil change every six months is your best ROI. If you were driving 15k+ every six months synthetics would be cost effective. But, if you prefer synthetics, have at it, you won't be hurting a thing!

 

Great write up. You exlpained it in laymans terms.

 

I'm cheap. I'm a miser. I hate wasting money. But the cost difference between regular oil and synthetic is so small, why is this even up for debate? Synthetic oil is about $4 more per quart. That's about $48 more per oil change. That's chump change compared to the cost of tires, fuel, car washes... EXHAUST TIPS. I've been known to go way past the manufacturer's recommended oil change intervals. Having synthetic oil in the car makes me a little less worried when I can't find time to change my oil.