High mileage oil ruined gas mileage?

[Rollo]

My wife has a 2015 Subaru Forester we purchased used in 2016 with about 11k miles on it. The first few oil changes were either completed at a Subaru dealer or by an oil change service using Pennzoil Ultra Platinum. I eventually began completing the oil changes myself using either Mobil 1 or Pennzoil full synthetic.

In late 2017 my wife purchased the oil for her oil change and I didn't actually pay attention to what she purchased. She had purchased the high mileage version of Pennzoil synthetic. Her car that had previously gotten 25 to 27 MPG immediately began getting only 22 MPG during the same exact type of driving.

I changed the oil again within a month or two and changed it again after just a few months and the poor gas mileage persisted. I have changed it 2 or 3 more times since then and the poor gas mileage still persists.

Is there anything I can do to safely clean out the engine of any residual material from the high mileage oil?

Thanks very much in advance.

 

[Lyman]

It's not the oil. Look elsewhere.

 

[CT8]

I doubt the oil makes that much difference in the mpgs.

 

[Trav]

Barking up the wrong tree. Check your plugs and air filter.

 

[LeakySeals]

Why was high mileage oil put in it at all? Was it a mistake at a quick lube or was it an experiment because of oil consumption?

 

[zzyzzx]

High mileage oil ruined gas mileage?

 

[spasm3]

Originally Posted by Rollo
My wife has a 2015 Subaru Forester we purchased used in 2016 with about 11k miles on it. The first few oil changes were either completed at a Subaru dealer or by an oil change service using Pennzoil Ultra Platinum. I eventually began completing the oil changes myself using either Mobil 1 or Pennzoil full synthetic.

In late 2017 my wife purchased the oil for her oil change and I didn't actually pay attention to what she purchased. She had purchased the high mileage version of Pennzoil synthetic. Her car that had previously gotten 25 to 27 MPG immediately began getting only 22 MPG during the same exact type of driving.

I changed the oil again within a month or two and changed it again after just a few months and the poor gas mileage persisted. I have changed it 2 or 3 more times since then and the poor gas mileage still persists.

Is there anything I can do to safely clean out the engine of any residual material from the high mileage oil?

Thanks very much in advance.


Not the oil and nothing of a high mileage oild needs to be cleaned out.

 

[ARCOgraphite]

I would initially say - Unrelated.

Possibly your VVT cam phaser is not functioning properly.

Get a scan tool on these systems and misfire counts and fuel trims and o2 lambda response.

Make sure oil level is correct. 5qt; NOT 5.5 or 6 quarts.

Did they service the diffs? Did they use 75W90 syn GL-5 ? Likely no.

I find many airboxes not sealed correctly. Check this too. The intake is a tuned resonant system and does not work if leaking.

Alignment , tire feathering, Tire pressure?

Wouldn't hurt to run a couple 1/2 bottles of Gumout Regaine PEA .every third tank.

What fuel?. Gas quality is garbage up here.

 

[Urshurak776]

No way. Not the oil.

 

[JohnnyJohnson]

Originally Posted by Blkstanger
It's not the oil. Look elsewhere.


This

 

[InhalingBullets]

Might also look at MAF sensor, PCV valve and correct tire pressure/

 

[dogememe]

Unless you put straight 50 in there the oil isn't making a difference in fuel economy. Something else is wrong with the car.

 

[kschachn]

Yeah, there is something wrong with your car if that is an accurate mileage measurement. Nothing to do with the oil.

 

[oil_film_movies]

Not the oil. At most, switching to a High Mileage oil of about the same viscosity would lower MPG by about 1%, at the most, that is. This is due to possible differences in the amount of moly friction modifier (FM), or some other form of FM which can affect fuel economy in small amounts, not the big amount you're talking about, no way.

MPG differences in oils are also due to viscosity differences as well as the FM differences I mentioned above. You get something like a 1% change in MPG as you go up or down a grade (as in, from a 20 to a 30, for example).

Tires underinflated by 3 psi can reduce MPG by about 1 MPG, so something to check there.

Usually the OBDII system will detect and light up a Check Engine Light if the engine is running too rich, since its a clear emissions issue.

 

[oldhp]

See if you knocked a wire off a sensor.

 

[dave1251]

The easiest check is to check your tire pressure. Oil is not going change FE by 10% or the oil pressure by 50% like a post yesterday.

 

[DGXR]

High mileage oils are known to be slightly thicker than their non-HM counterparts, but not by much... certainly not enough to affect MPGs as much as reported.

 

[geeman789]

High Mileage oils are really not very different from a 'regular ... " oil. The number one difference is that they are almost always closer to the top of the allowable viscosity range for the grade ( THICKER). They usually have a tweaked additive mix, with slightly more seal conditioning additives being common.

They are an excellent way for the oil maker to generate additional profit. Add a few pennies to the cost, and charge a few dollars more for the oil ... !

 

[kschachn]

Originally Posted by geeman789
They are an excellent way for the oil maker to generate additional profit. Add a few pennies to the cost, and charge a few dollars more for the oil ... !

Here in the Milwaukee area at least, at Walmart they are the same price as the non HM products. For example, M1 5W-30 and 5W-30 HM are both $25.47 for 5 quarts.

 

[anndel]

Originally Posted by kschachn
Originally Posted by geeman789
They are an excellent way for the oil maker to generate additional profit. Add a few pennies to the cost, and charge a few dollars more for the oil ... !

Here in the Milwaukee area at least, at Walmart they are the same price as the non HM products. For example, M1 5W-30 and 5W-30 HM are both $25.47 for 5 quarts.


Same price here as well. Looking at PQIA data for regular M1 and HM oils, HM oils has a bit more Zinc and Moly. I ran both in our cars and MPG was the same.