Synthetic Oil (full synthetic) Vs. Conventional- Change Frequency

Please, if possible, I would like to hold the discussion specifically to 2016/2017 Subaru Outbacks, 3.6R (6 cylinder) and am searching for Subaru company facts and your sources if possible.
I own a 2017 Subaru Outback Limited 3.6 R (6 cyl.) Subaru Company advertises to change Conventional oil every 6,000 miles. Subaru Company Owner’s Manual also says I can use Synthetic 5W-30 as long as it meets the common oil designations.
When I bought the car, I bought the dealer sales dept. recommended and I bought a 3 oil change package (full synthetic).
The rub is my dealer Service Dept. (SD) says if I insist on using synthetic I should change it every 3,000 miles because the 3.6R runs hotter.
History- at 5,500 miles, the SD changed the oil and replaced with synthetic and placed a sticker saying change it at 11,500 miles.
At 11,500 the SD changed the oil and put in Conventional oil and placed a sticker that said change at 17,500 miles. I asked them why Conventional and they said Subaru recommends Conventional because the 6 cyl. engine runs hotter.
Today at 11,700 miles, I went back and asked the SD to put in Synthetic; they did, and placed a sticker that says change the oil at 14,700 miles. I asked why 14,700 and they said the Synthetic will break down due to the heat the 6 cyl. produces.
I would never run Conventional oil for 6,000 miles (maybe 4,000) but am concerned about warranty implications.

Forget what anyone at the dealer said. Follow the owner’s annual. Synthetic oil has far more heat resistance than conventional oil and will stand up better to heat.

The dealer service dept wants to sell more oil unnecessarily. They make more money that way!

Yours is the very first post ever about changing oil more frequently with synthetic oil.

Your owner’s annual will likely say the same interval for both types of oil…

The 3000 mile interval is almost unheard of these days; Toyota now calls for 10,000 miles and both our vehicles have 6000 mile intervals with or without synthetic oil.

A down to earth comparison would be to compare regular oil with butter and synthetic with a good vegetable oil. The vegetable oil handles heat a lot better than butter in the frying pan.


Ignore the dealership…follow your owners manual


That SD lost all credibility with the story that the 3.6 runs hotter and with synthetic needs 3,000 mile oil changes. What a crock!

A service adviser at a Honda dealer told me that Honda recommends against synthetic oil because it doesn’t have enough…(he paused looking for the word)… grit!

:man_facepalming::man_facepalming::man_facepalming: Wow…

True Grit…what every engine needs…

I’ve stopped listening to “service advisers”. I take the owner’s manual with me and when I hear one of those B.S. pitches, I refer to the appropriate page in the manual and tell them that’s what I want done.

Most service advisers would flunk High School chemistry and are clueless about things like Viscosity Index and other measures of an oil’s ability to lubricate.

So true…service advisers are among the most useless people out there

As others have said…follow the owners manual.

I’ve yet to see a service manager who knows anything about cars. I bought my Highlander from a large Toyota dealer. Just recently they were advertising to hire more service writers.

Requirements- No experience, but 2yr Associate degree in Business is preferred. No where in their requirements did they say the person needed any mechanical knowledge.

WOW… I suspected that, but had hoped some of them has some knowledge. And the service writer is really the face of the dealer, once you have purchased the car.

Objective information would be helpful: 1) consider performing a used oil analysis after 6000mi. on successive fills of conventional and synthetic, with perhaps an intermediate analysis at 3000mi (pull it from the dip stick tube). Consider using oils by the same (major) brand, perhaps Subaru’s (made by Idemitsu). Keep the use conditions (driving type, climate) similar, try to include the same number of cold and warm months. 2) To determine if the oil truly runs hot, measure its temperature after an hour of steady running on a warm day (use a surface thermometer or a non-contacting thermometer on the oil pan or stick a thermocouple down the dipstick tube) and compare to the recommended operating range.

For what it’s worth we have a 6cyl. 2006 3.0L Outback and compared Subaru brand conventional and synthetic and Mobile 1 (their regular “synthetic”) on two fast, hot cross country trips last summer - the conventional was changed at 5700mi., looked okay, but over the last several hundred miles it felt less lubricative between the fingers oil consumption increased (no make up needed). The synthetic went 6700mi. with consumption rate also accelerating near the end and required 1/2- 3/4 qt. of make-up. The standard grade of Mobile 1 performed similarly to the synthetic Subaru. Gas mileage records showed no differences between the oils.

I used to own 5 Subies in the past, before partying to other car makes.

Never used [overprised?] Subaru oil, but always used synthetics.

I found Valvoline SuperSyn to have the least of oil burn (under quart) over 5000 miles OCIs I used to observe.
Mobil 1 was definitely more burn, I had to add 1…1.5 quarts over that 5000 miles, while on Valvoline I would have around 0.5 quarts down, so I did not need to add any.

I switched to Valvoline after looking for the oil with the lowest Noack on specs, from types I would get off the local store.

Subies are known for their oil consumption.
At first, once I learned it I freaked. Their official position is “we do not consider this consumption excessive if it can not be demonstrated to exceed 1 quart per 1000 miles”… just relax and make sure you check oil often, at least until you know your regular consumption over 2-3 intervals.

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Hi Antonio, I also have a 2017 Outback 3.6R. I agree with the other responders above, go by the Owners Manual, not what you hear at the dealership. Actually, our owners manual says:
"Your vehicle is designed to use 5W-30 conventional motor oil, however 5W-30 synthetic may be used for optimum engine performance."
It goes on to describe the oil quality requirements. I’ve gotten similar BS from dealers, but you can’t go wrong following the manual. I believe that synthetic oil should generally last longer than conventional oil; but since the maintenance interval is only 6 months/6000 miles for replacing the oil and filter I’m just using conventional oil during the warranty period. My wife’s 2013 Lexus manual recommends using synthetic oil in that car with oil changes every 12 months/10000 miles. Of course, all that assumes reasonable duty for the oil. We normally have significantly lower mileage (about 4000 to 5000 miles / 6 months) on each car. Of course, if you have difficult driving conditions or you plan to keep the car well beyond the warranty period then synthetic may be your best choice.

There are a number of things a service writer needs to be successful at the job. Hands-on mechanical knowledge or experience isn’t in the top 5 of the list.

I currently have the pleasure of working with the best service adviser I’ve encountered in 30 years in this industry. Her work history includes food service, convenience store clerk and management, and home cleaning service. Her mechanical background? Her son races circle track cars. She knows what a transmission does, what an alternator is for, and driving with the oil light on is a bad thing. Beyond that, what does she need to know?

She has the ability to listen to what a customer is saying, the ability to write that on a repair order so the tech knows what to fix, the ability to explain to the customer what we found, how much it will cost and why they should fix it, and to set customer expectations. The technical mechanical side of auto repair belongs in the shop with the mechanic, the people and business side of it is at the counter with the service writer.


You do realize there’s a difference between a service manager and service writers right?

Now I’m really confused. Our '16 Outback 4 cyl. has an oil temperature readout on the touchscreen. Wouldn’t that be true for the 6 cyl?

Sorry, I’m not familiar with the newer Outbacks (my 2006 OB is pre-touch screen) but it’s great if the original poster’s car has an oil temperature readout as that would provide an easy way to check the assertion about higher oil temps.

I tend to agree with @asemaster

The successful service writers I worked with weren’t very technical-minded

Those service writers who had been mechanics unfortunately weren’t very good at selling. Yes, that’s what service advisors are. Even if somebody chooses to think a service advisor is “on their side” they’re still salesmen. And if a service advisor forgets that, they won’t be able to put food on the dinner table and pay the bills.

Despite Subaru having that stupid 6K oil change interval you’re still better using a synthetic. Costco has coupons sales on Mobile One and it won’t even cost you any more than conventional. Synthetics avoid sludge buildup.

I think where customers get in trouble with service writers and service writers get in trouble with customers is when the service writer gives technical advice beyond their level of knowledge. A perfect example is how this post started.

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