Does synthetic oil make a difference?

July 29, 2009 7:56 AM

Is synthetic oil worth the premium price for a Honda Accord with 140,000 miles?

I've been relatively consistent with oil changes (between 3750 and 5000 miles) with conventional oil. The oil change place tries to talk me into high mileage or synthetic oil every time, which seems like it may be a scam.

Previous questions here mention using synthetic oil in passing, but nothing definitive that synthetic is better than conventional. Similarly, Google searches don't seem to reveal any scientific evidence for synthetic over conventional.

Do any manufacturers actually recommend synthetic over conventional? I would think that if it actually made a difference that manufacturers would recommend it.

posted by dforemsky to travel & transportation (10 comments total)

Do any manufacturers actually recommend synthetic over conventional?

Yes. Except for break-in, it's a proven superior oil.* The big reason is that the composition is much more consistent than conventional motor oils. It lasts longer and lubricates better, and it has better viscosity characteristics. Most manufactures now ship cars, and specify, synthetic oils -- in particular, Honda and Ford now specify 5W20 or 0W15 synthetic oils on almost all cars -- and get 10K miles between oil changes.

* And that's break-in on older cars. Modern engines are built to much tighter tolerances, and don't need the long break-in process that older cars did.
posted by eriko at 8:25 AM on July 29 [1 favorite has favorites]

My friend and I are both Mobil1 snobs. You are specifically not supposed to change it until 5000 miles, they actually make a 7500 mile version. His accord (which I am currently driving as a daily driver, the Hemi Durango gets it too) has about 245,000 miles on it. No joke. No internal engine repairs since he's had it (he got it at 117k), doesn't know the provenance beyond that.

It's definitely worth doing it yourself though. My durango takes 7 quarts of the stuff, costs about $39 retail, plus an upper level filter for ~$11. Same change at a shop costs something nuts like $129 plus disposal fee.

There is a rumor that because of the smaller molecule size in synthetic, that it might actually leak in seals conditioned with old oil. I used to have an '82 Kawasaki 440KZ rat bike with an unknown number of miles that had been sitting for ~2 years. I put mobil 1 in it too, and nary a problem.

YMMV. IRL.
posted by TomMelee at 8:38 AM on July 29

The high mileage oil is useful is you have oil seepage from your seals. The zinc in the high mileage oil will swell the seals a bit and slow or stop the seepage. It also can help quite noisy valves. However, once you go high mileage oil you have to stick with it as the leaks can be worse if you go back to conventional oil.

I drive a 97 Mazda with 140K miles that has only used conventional oil. I'm going to ask the shop about the high mileage stuff next week as the oil on my driveway is becoming a problem. It still only amounts to a quart every 2000 miles though.
posted by COD at 8:39 AM on July 29

Yes, synthetic is better in every way but it's not magic. Let's say it's the difference between making it to 175K vs 200K miles between rebuilds. An extra $20 per oil change, every 5K miles, over 175K miles is $700. IMO, it's kinda a wash.

FWIW, my '91 BMW has 225K miles on the original motor, almost none of it spent running synthetic, and the compression is within 5% of spec. My '88 BMW had something way over 225K on it, also running non-synthetic its whole life. My dad's got a BMW with 260K on the original engine, also not running synthetic most of its life. Do I see the need to switch to synthetic now? No, not really. :)
posted by paanta at 9:20 AM on July 29

My son said a Ford truck engineer told him that if you use 20% synthetic you get 80% of the benefits.
posted by JohnR at 9:56 AM on July 29

I know the big three do: BMW, Audi, and Mercedes. Porsche too. It's the only sort of oil approved.
posted by luckypozzo at 10:33 AM on July 29

(Retired mechanic opinion) My preference was to use one quart of synthetic with the remainder a top brand of the appropriate grade and change the oil every 3,000 miles. Back in the day, an engineer came to our class and talked about oil quality. He said that regular multi-grade oil breaks down, especially after 3K miles of use in the city, like most of us drive. The superior quality synthetics he had tested were essentially as good as new after 80,000 miles, although he did change oil filters twice a year, and top up the level. He recommended Castrol, Kendall, or Quaker State and said avoid Pennzoil, and to never use Fram filters, which are crap, but to use the filters manufactured by the make of vehicle. Using at least a portion of synthetic can extend the period of virtually no engine wear dramatically, and is well worth the expense.
Using 100% synthetic, then throwing it out at every oil change is a waste.
posted by sugarbx19 at 12:07 PM on July 29

There's a lot of good data on this site. Long story short, you can go well over 10,000 miles without changing and not worry (too much) about the lubricant. What's that worth to you? In this case YMMV should be taken literally.
posted by 1f2frfbf at 12:08 PM on July 29

The above is pretty comprehensive; there are a few points to emphasize:

1: You are changing your oil frequently and keeping up with regular preventive maintenance like that will keep you in good shape. However, you're doing it at an oil change place which deprives you of one of the best reasons for oil changing: -your own- check under the hood. If you really trust the oil change place to do that for you, that's fine.

2: There is a lot of anecdotal evidence on legacygt.com that changing to a synthetic so late in the engine's life will -increase- oil leakage. TomMelee makes this point but I suspect it is worth repeating. The suspicion most commonly voiced on legacygt.com is the detergents in the synthetic are a bit more aggressive and they clean off the schmutz that's actually part of the seal.

3: Again, beware of oil filters. Subaru used to have their filters made by Toyo Roki which were excellent. They recently changed their North American OEM to Honeywell, maker of Fram filters. Accordingly there's a massive shift among Subaru nuts to Mobil 1, Wix or Purolator filters all of which are hands down superior to anything Fram makes.

4: Engine longevity is composed of design, driving habits, maintenace and luck. 140k on an Accord doesn't seem that high. My '84 Civic made it to 280k miles on plain old dino oil and my old Subaru just turned over to 270k - again, on dino. My newer Subaru is turbocharged and therefore I switched over to Mobil 1 at 10k miles. Many Subie people say the Mobil 1 burns off at a quart or so per 5000 miles even if they were burning no dino oil and I won't gainsay them but it hasn't happened to me. There is a German Castrol synthetic that a lot of these people swear by.
posted by jet_silver at 1:02 PM on July 29

The superior quality synthetics he had tested were essentially as good as new after 80,000 miles, although he did change oil filters twice a year, and top up the level.

That is partially missing the point, and changing your oil regularly is NOT just about removing the oil because it is breaking down. You are also removing the particulates (including the ones too small to be filtered out) that your engine produces as part of it's function. Flushing your engine of these is important and regular filter changes are part (but are not all) of that process.

Synthetic oil is better than organic in all aspects. It is well worth it on all but the rattiest cars. With an older car, you can stretch your oil changes more with synthetic, but it still needs regular changes. It is never bad to change your oil more regularly, just becomes of diminishing returns In terms of cost if you do it more often than 3-5k miles (in a standard, reasonably normal power output engine).
posted by Brockles at 4:31 PM on July 29