[ForesterBill]

I think you would benefit from a 5W30 high-mileage oil like this:

Full Synthetic High Mileage with MaxLife Technology - Valvoline™ Global

As engines grow older, they can consume oil faster. You may even start noticing oil spots on your driveway or in the garage. Valvoline Full Synthetic High Milage Motor Oil with Enhanced MaxLife Technology is formulated to address issues with oil consumption, oil leaks, wear, heat and reduced...

www.valvoline.com

 

[Scobar]

I have a 2015 Forester Limited. I bought it new. Just passed 100k miles and starting to see a little oil use. Having to add a quart near the end of the last 2 6000 mile oil change intervals. Anything I should be worried about?

 

[adc]

If you are using 0W20 switch to 5W-30

 

[DragonSubie7]

A quart in 6000 miles isn't all that bad, but you might try a higher viscosity/high mileage oil and see how that works.
I switched to a higher weight high mileage synthetic.
Mobil One and many others have those formulations. There are others.

In my case my similar FB25 drinks 0-20 and doesn't use any since I switched. 5-30 winter / 10-30 summer.
YMMV

 

[Theseus161]

With FB series engines, I would not use 6k mile OCI. 5k tops and 3k for severe duty, like short trips. Time as well. 6 months ? Try 3-4

Oil shear/thinning and dilution. Fuel in the oil mix. 5-30 instead of 0-20 is a good idea. Especially before any consumption problems.

I’m close to 100k miles. Engine uses maybe 2 ounce of oil. We will see what happens.

 

[wmederski]

Wanting to tell the tale of my 2011 Forester X Premium.
Bought in July 2020, $10K with 55k on it, retiree owned, garage kept. Looked new inside. I put 30k on it without issue. Adding 1-2QT between 7500 mile oil changes.
Then last summer took it from Texas to PNW and back, totally 6k miles. Expecting hot weather and highway miles, I put in M1 5W-30 before the trip. It ended up drinking 1QT every 1k miles!

Got back home and took it to Austin Subaru for an Oil Consumption Test. Knowing that it was mostly an issue with highway miles, I took it on a 1000 mile highway rounder and it failed the OCT.
Since it was over the 10 year mark, but still under the 100,000 mile mark, SOA had me pay a $1000 deductible towards the Short Block swap. Had the work done and got the car back in January of this year.

I babied it for the first 1000 miles, keeping it under 3K RPM. Then took it on another long rounder of highway miles before planning an oil change at around 2600 miles post-Short Block swap. I had noticed the oil level was dropping a bit, and notified my Subaru rep. Did a proper oil level check and it was about 1/4" from the Low mark on the dipstick... Subaru rep told me to bring it on in. It was 1.8QTs low! Underside of the engine is spotless, and I put some white gaf tape above the exhaust tips to see if I could catch some oil burning through the exhaust, but none showed up...
He acknowledged that occasionally they see Short Block swaps not go right and offered another OCT, free of charge. <eyeroll>

Did another long highway rounder last week, 80mph vs my typical <75mph cruising speed, pushing the car a bit over the 1400 miles.
But it didn't seem to be drinking oil like it did after the engine work... Just took it in yesterday and it was only 0.3QT low. So it passed the OCT. <shrug>
The tech and myself both figure it was a matter of the piston rings not seating right, perhaps until I leaned into the car a bit after the second oil change since the Short Black swap.

I still have until January for the work warranty, and will definitely be keeping a very close eye on it all. But it's a little baffling how much cars are expected to consume oil these days. This is the newest vehicle I've every owned, having mostly maintained beaters that I expected to be leaking and burning oil.
My pops just took delivery of a brand new Porsche and was told to expect 1QT every 1500 miles while the car is new. And 1QT between changes thereafter. Which is just wild in my mind, for top notch German engineering. (oh, and there is no dipstick. just a digital gauge in the cluster)

Then again, there is a reasonable argument that letting a little oil passed the rings helps lubrication and cylinder lifespan.

 

[cherijo]

As has been typical, from Day One (<25 miles on the Odo), our '11 PZEV Fozzie has consumed oil. We missed the settlement/warranty window for various reasons, and it hadn't been a problem to that point. Fast forward to today, now over 170k. We now use a quart about every 2 tanks (call it 500 miles). Some of it is leakage from the typical faulty seals, some is likely burnage, especially when we tow our tent trailer or I'm climbing around offroad. I've used good synth 0w20 religiously, but lately the rate is costing us a fair amount.

We just replaced the cat (gave out at 168k, in March 2023) and O2 sensors and are having intermittent trouble with the downstream sensor indicating a P0420 fault showing 0V issues with Freeze Frame data (I don't have a live reader... yet), but ONLY at highway speeds. I've reset it and had it go 6 weeks with no issue. It's ALWAYS at highway speeds with cruise control on. I'm having the system re-checked for downstream leaks, etc; (Might need to do the 2nd cat as well?). One of the possibilities is that the excessive oil consumption is fouling the sensor up. The cat replacement took us back to our typical factory estimated 24MPG mixed use (21 city/27 highway EPA), up from about 21 pre cat replacement. There's been no loss of power or MPG with the "new" sensor issue since the main cat was replaced in March 2023.

After plowing through both all the related oil type discussions and O2 sensor issues, I'm left considering switching to 5w30 synthetic to see if this helps out my consumption issues, potentially making my new cat/sensors happier long term. Given I'm at 170k+, there's no warranty issues. I'm sure the block/piston rings are starting to wear in nicely by now, occasionally I think I'm starting to hear a bit of piston slap (predictably worse when the oil gets low; sounds like a diesel shutting down if I drop just off the stick), so I'm wondering if switching to 5w30 synthetic could help my engine be a bit happier until I'm ready to do an engine replacement? I don't have the money to do it right now, but it's in my long term plans because I LOVE my 4-speed fozzie. We live in the Seattle area, very temperate. At worst we MIGHT hit 12°F (-11°C) in winter, so I wouldn't think the 5w over 0w would mean much really. It's the 20 to 30 change I'm more interested in exploring given the FB engine.

So, what's your (informed please!) opinion? Could switching help me burn less oil out and slow down wear a bit in a higher mileage FB engine? Or am I courting earlier failure?
(Please keep in mind I'm not ignoring other potential sources of the P0420 code; they'll be chased down simultaneously. This is just one piece of the overall puzzle.)

 

[551602]

I use 5w30 in mine with a can of Liqui Moly Anti-friction MOS2 supplement every oil change. The anti-friction provides extra engine wear protection, is good for the timing chain, and quiets the engine down nicely. I tend to add about half a quart of oil per month, sometimes less. It's running nicely so I will keep doing it. I have roughly 190,000 miles on mine (293,500 KM)). I replaced the 02 sensors 3+ years ago but the cat and the rest of the exhaust are still original.

 

[Black21Limited]

The double edged sword of synthetic is it can get into places that conventional oil can't. It's a plus for lubrication and flow, but not so much for going places you don't need or want it to, like getting by old seals, and sub par oil control rings.


You could try a 5w-30 conventional to help slow the bleeding. That's what I did on my high mileage Dodge neon I had. (synthetic wasn't specified but the PO used it, and I just continued) It used a bit less oil, and the oil wasn't quite as expensive. Unfortunately the price gap isn't as wide as it used to be for brand name conventional vs synthetic.

Being it's still going to consume oil, you're still going to be refreshing the oil, so even conventional isn't going to be in there long enough to breakdown to the point it is doing any damage. In reality, the damage is already done.

The oil burning, and going out the tailpipe isn't helping the o2 sensors. With EGR going, it's also adding to the blowby from the crankcase being pulled from the PCV valve. The inside of the intake manifold is probably pretty nasty.

At least the neons didn't have EGR after 1999, so that was a huge plus. I had a Mitsubishi 3.0 that a PO abused, that would smoke worse than a 1960's Ford at a stop light. When I pulled the intake manifold off, it was probably the worst thing I have seen, between the EGR and the PCV filling it with gunk. It was like a black tar. But at least with the port injection the intake valves were still clean!

 

[Vishnu]

Changing oil viscosity won't stop or slow oil consumption. You have to fix the problem to make it stop.

 

[551602]

Actually, in point of fact, it does lessen oil consumption and provide better engine protection. The early FB25s will consume some oil. Telling someone they need an engine overhaul or short block replacement is not helpful and exaggerates the severity of the issue. I recommend the OC try using 5w30, the additive I suggested above, and then report back. I am sure he will find the result is a quieter engine and less oil consumption.

 

[KW England]

I tried some Liqui-Moly for my small oil leak, but it didn't seem to help much. I would still give Quadraria10's suggestion a go, if I was the OP or had more or a leak than I do.

 

[551602]

That was a different product, namely their oil saver which has been quite good at limiting the leaks on mine and has actually stopped a couple of leaks that were problematic.
Here is the link to the Anti-Friction product details. MoS2 Anti-Friction Engine Treatment
I use it to combat wear and tear, particularly for the timing chain system, and for protection in case of oil loss. It's cheaper than buying Liqui Moly branded oil. I use it with Wal-Mart super tech synthetic 5w30. The object for me is to maximize the operating life of my engine.

 

[adc]

Changing oil viscosity won't stop or slow oil consumption. You have to fix the problem to make it stop.

Boxer engines start using oil at 150K miles in general. Switch to 5W-30 or 5W-40 or 0w-40. My '22 Forester gets 5W-40 Mobil 1 and my 18XT gets 0W-30. These days there is almost no difference syn and "dino" oil.

The only "True" syns are Motul, RedLine, Amsoil, RP, Schaffer's. 0W-40 Mobil 1 has some syn.
My 08 started using serious oil at 150K miles. 40 wt oil totally fixed it.

 

[Vishnu]

Good luck with that. Any chance they started using oil after they were fed 40w?

 

[adc]

Good luck with that. Any chance they started using oil after they were fed 40w?

Zero chance. Many thousands of research hours on Bearings and Lubrication Science (Tribology) over the last 55 years tells me that.

 

[Vishnu]

Perhaps Subaru needs to hire a/some better tribologists and revise their current oil viscosity requirements. Doing so back in 2014 might have saved them millions of dollars by simply raising the viscosity ratings higher as a cure to their oil consumption disaster. Where in heaven's name were the tribologists then?

To all the tribologists out there, what is the crankcase upper viscosity limit (if there is one);40w? 50w? 60w? Or 90w? When does viscosity even matter? My '21 is only 60,000 miles from the oil consumption trigger point adc quoted and I want to be ready.

 

[DragonSubie7]

Perhaps Subaru should ignore the minimal gains in CAFE numbers which was the major reason for all manufacturers to require low viscosity oils, but they won't.

As to viscosity not affecting oil consumption, this theory doesn't match the facts I've observed.
Some theories are just that - Potentially true ideas that should be fact checked.
This theory fails.

My FB25 hasn't used ANY oil this summer with 10-30, while it would go through quarts of 0-20.
It's been using 5-30 / 10-30 for ~ 6 years now with no issues.
YMMV

Here's a snippet from Mobil Oil that seems to support the position @adc proffered.
"
Should my oil choice change as my vehicle gets older?
Yes, your car’s preferences will change with time. Vehicles with older engines benefit from thicker oils that prevent friction and oil loss whereas newer vehicles benefit from thinner oils for faster lubrication of new engine parts.

If older engines are not replaced with high-viscosity oil, it can lead to problems such as noisiness and increased wear. This is important to consider as your vehicle enters more advanced stages of its lifecycle."

 

[Vishnu]

I personally love the mileage my '21 gets and you should be seeing some oil consumption between changes. To be clear, if the level stays the same or goes up, then it's being diluted from blow-by or raw fuel. But I don't think you meant you see zero loss. I found that article you quoted from Mobil and it does make that claim, but doesn't make any suggestions other than don't go too high with the viscosity. It made me curious to know if their "high mileage" branded oils actually have higher viscosity than stated on the label compared to non high mileage oils. But I had a '14 that got the new block and I can attest that upping the viscosity had no affect on the oil consumption. Take it from the horse's mouth.......

Here's a pretty good, and short, run down on the subject (w/pictures!):

Oil Viscosity - MotorWeek

motorweek.org

And another point to ponder is what happens in cold temps when you crank that cold engine and you subbed out a higher viscosity oil for the manufacturer's specified viscosity oil? I am not a tribologist, but I am pretty sure the engine isn't getting adequate lubrication until about ten miles down the road when things warm up to operating temperature. Wear is going to happen, but why rush things?

This has been a productive post for myself. Because of Mobil's viscosity upgrade per engine age statement, from now on I plan to blend 5w-30 and 0w-20 in the ratio of 1:4 +/-. As my engine ages the ratio can go to 2:4, and finally 3 qts. 5w-30 and the rest in 0w-20. Thanks all. Maybe we can report analysis reports for differential brand blends until the "final word" on oil blends is found.

 

[DragonSubie7]

I am not a tribologist, but I am pretty sure the engine isn't getting adequate lubrication until about ten miles down the road when things warm up to operating temperature. Wear is going to happen, but why rush things?

You being "pretty sure" somehow doesn't convince me.
A car does not need zero weight oil unless operated in truly frigid temperatures.

The article you quoted said "My recommendation, stick with what the vehicle manufacturer recommends. They spend millions of dollars figuring out what was right for your engine."
Conveniently not mentioned is that they save millions of dollars by towing the line on the CAFE recommendations.

One could also mention that the Subaru engineers created a sealed CVT and recommended that it never needed fluid changes, because it was a lifetime fluid (oops!) and developed a gasket seal for their EJ engines that was guaranteed to fail.

The point is, in some cases what is recommended can turn out to be less than ideal.

It seems you now agree with the fact that as engines age, they loosen up and need higher viscosity oil to ensure proper lubrication, or in the case of the earlier FB25, what I and others have found is that these engines are helped considerably as to oil loss when a heavier weight oil is used.

In any case, your MY21 is not the same engine this oil use thread was intended to be about.
Maybe you will do fine forever with the 0-20. Why change something that works?
Or maybe not in the longer term, if you start noticing oil loss, try a heavier high mileage formula.
Or not.

In my case I didn't change the oil viscosity until I needed to, and then it made a very positive difference.
YMMV