Synthetic or reg oil for 90K servicing?

At 85K on a 2003 Subaru Outback H6 VDC we just picked up, we’ll probably do the 90K servicing now. Would you use synthetic or reg oil, and why?

Doesn’t really matter which you use if you change your oil regularly and aren’t subjecting the car to brutal conditions (racing, expeditions into the desert, operation in 10 degree weather). You’ll get more benefits from regular oil changes with standard oil, than from extended changes with synthetic. Synthetic today mainly offers a benefit of better flow at very low temperatures and better stability under extreme use. If you happen to live in the Dakotas or somewhere where the temperature gets very low synthetic might not be a bad idea, but otherwise you’ll be fine. Also, if subaru specifically recommends it in the owners manual for this engine then that’s another reason to use it.

Today’s oils are very good. The issue is whether you can retrieve the extra cost of a synthetic oil change vs conv oil. I run 5K intervals on conv oil in our Subarus and 7.5K mi intervals for synthetic. That allows me to schedule my oil changes so I don’t do one in dead of winter and I retrieve the extra cost of the synthetic accordingly. Due to several sales and rebates, I am running synthetic in our daily drivers. If I were going to a mechanic for my oil changes, then I would overwhelmingly stay with conventional.

I don’t know how true this is, but I was told that that high mileage oil is better quality than regular oil but costs less than synthetic. Maybe you can ask about that, I haven’t been able to look up the validity of the claim.

My car (98 Saturn) has 125K miles and consumes less than a quart in 3000. Every time I go in for an oil change (3000 miles) they’re pushing “high mileage” oil, which of course is more expensive. What is the criteria for switching over to “high mileage” oil? Do I reduce engine wear enough to offset the price increase?

If your engine is starting to burn oil substantially (which yours isn’t) or it’s starting to drip from the seals then high mileage oil is supposed to help.

High mileage oils all have special conditioner additives to help swell seals, etc, because over time seals shrink. I seldom use high mileage oils (once I think in my 95 Ford F350) and would not substitute it for synthetic. Unless I have excessive oil consumption I stick with conventional or synthetic. The one time I used the high mileage oil I saw no difference in oil consumption (which wasn’t all that high, anyway; less than one quart per 5K miles), so I see no need to use it in my vehicles. Most oil change places push some level of high mileage or premium oil changes, when most of us all need just the conventional oil. One of our family vehicles is a 94 Prizm and it still gets conventional oil changes, little oil consumption in 5K miles, and 225K mi on the odometer. This convinces me that high mileage oils are generally not needed.

High mileage oil is better at only one thing, reducing oil usage of worn or old engines. It is not better for most cars and may not be as good.

Find the owner’s manual. See what it says. If it does not say synthetic, then you can use either. If it says synthetic, don’t use regular oil.

You can always use synthetic, but you should always follow the recommended oil change schedule in the owner’s manual.

Agree with Joseph; high mileage oil will get some more miles out of a well worn engine without consuming too much oil. It migth also allow an old engine to meet the emission tests. That’s one reason it is heavily advertised on the sports networks, and not as much in upscale car magazines. Quaker State, part of the Shell family, has built some kind of cult status aound their oil.

It’s not a good idea to use this high mileage oil in a tightly sealing engine, regardless of age. It’s more expensive, and may increase wear on startup in a tight engine.