2019 Subaru Ascent FA24, 7.1k, HPL PCMO 5w30

[Hohn]

I’m going to have to do a better job of proofing my posts. Cringe-inducing spelling and composition errors cannot be edited later!

One reason I’m so set on the intake air temp aspect of this is because elevating the oil temps only helps with the fuel that is *already* in your oil. And it does little good to run an hour at highway speeds and elevated oil temps in an attempt to burn off fuel when your making more fuel dilution as fast as you can burn it off.

So I think you need a two-prong approach: elevated oil temps to help cook off some of the fuel dilution, but 2) prevent fuel dilution with warmer intake temps. The prevention is arguably more important because it keeps your oil from having to manage that contamination.

 

[scrllock]

There’s no shear here. It’s pure dilution. The last run was with No VII series and still lost about 0.5cSt, which I could give a flip about since I’m not using a 20 grade.

Ah, I thought this was PCMO, not No VII.

I liked the idea about the thermal valve, not allowing coolant to flow thru the cooler until the oil is at least 200* or so…. Will have to look into that.

This is a bad idea. Your coolant gets up to temp much, much faster than the oil. This would make it take even longer for the oil to come up to temp. This is a key function of OEM oil to coolant heat exchangers.

 

[tired]

There’s no shear here. It’s pure dilution. The last run was with No VII series and still lost about 0.5cSt, which I could give a flip about since I’m not using a 20 grade.

I’m going to make a point that before the next oil change, I’m going to spend at least 15-20 minutes with the oil 212*F or above and then drain a sample immediately since I’ve got a Stahlbus valve.

I don’t agree with your thoughts on oil temps in the 180s not being a contributor; the last UOA was a summertime sample with just her local trips, so ~15 miles each way, in ambient temps of 75-90*F, and oil temps maxed out between 196-198*F, which returned 7% fuel. This UOA like I said had probably 500 miles at various times where the oil temp was 215+, and it was the lowest fuel result even though there was some extended idling due to early-onset winter here. I liked the idea about the thermal valve, not allowing coolant to flow thru the cooler until the oil is at least 200* or so…. Will have to look into that.

Before doing all sorts of gymnastics under the hood like removing the oil cooler and doing a ton of extra driving at higher RPMs etc etc, have you considered reducing your OCI? Not great that it was diluted out of the 30 grade... Wonder how long you were driving with it out of grade.

 

[Hohn]

@SubieRubyRoo your HPL is keeping iron under 1.5ppm/1K miles even as dilution creeps up near 5%. That’s some very impressive performance if you ask me. I’m thinking many oils struggle to keep it under 2ppm/1k even with next to no diliution. The few that can certainly aren’t doing it in a Subaru!

And the undiluted KV100 of 10.1 per @RDY4WAR calculation shows that your 5w-30 sheared almost nothing in 7k miles. The dilution is the entire source of KV100 loss, or nearly so.


IN sidebar and offline discussions, I’ve begun making the argument that HPL’s barebones PCMO is an absolutely killer oil for the money, and is the real star of the HPL line. The upgrades to base and VII in the other main lines are upgrades most people do not need or benefit from except in specialty duty cycles. HPL wisely makes PCMO robust by spending the money on the co-bases, add packs and top treat. That’s what separates basic PCMO from a typical group III and why I think that basic PCMO is a heck of a deal. It is supremely intelligently engineered in terms of value, spending the money on what moves the needle for performance rather than just doing PAO for PAO sake.

I’m not saying PAO is bad thing by any means. I’m just saying that the cost premium is only justified in a handful of applications, niche roles that don’t apply to most street driver cars where a -40 pour points is sufficient. I’d much rather the cost premium be spent on some Esterex, Synnestic, and Molyvan than on upgrading the base to PAO.

 

[SubieRubyRoo]

Ah, I thought this was PCMO, not No VII.




This is a bad idea. Your coolant gets up to temp much, much faster than the oil. This would make it take even longer for the oil to come up to temp. This is a key function of OEM oil to coolant heat exchangers.

This run was PCMO, prior run was No VII. Had even more dilution but stayed in 30 grade viscosity.

 

[RDY4WAR]

Delete.

 

[SubieRubyRoo]

Before doing all sorts of gymnastics under the hood like removing the oil cooler and doing a ton of extra driving at higher RPMs etc etc, have you considered reducing your OCI? Not great that it was diluted out of the 30 grade... Wonder how long you were driving with it out of grade.

Considering the OEM recommends 20 grade, I don’t care one bit about ending viscosity at 8.7.

Besides, the oil cooler is on the top of the engine, right under the oil filter. Not sure why you’re so averse to oil running at 212* or above, especially an oil as robust as this?

 

[SubieRubyRoo]

@SubieRubyRoo your HPL is keeping iron under 1.5ppm/1K miles even as dilution creeps up near 5%. That’s some very impressive performance if you ask me. I’m thinking many oils struggle to keep it under 2ppm/1k even with next to no diliution. The few that can certainly aren’t doing it in a Subaru!

And the undiluted KV100 of 10.1 per @RDY4WAR calculation shows that your 5w-30 sheared almost nothing in 7k miles. The dilution is the entire source of KV100 loss, or nearly so.


IN sidebar and offline discussions, I’ve begun making the argument that HPL’s barebones PCMO is an absolutely killer oil for the money, and is the real star of the HPL line. The upgrades to base and VII in the other main lines are upgrades most people do not need or benefit from except in specialty duty cycles. HPL wisely makes PCMO robust by spending the money on the co-bases, add packs and top treat. That’s what separates basic PCMO from a typical group III and why I think that basic PCMO is a heck of a deal. It is supremely intelligently engineered in terms of value, spending the money on what moves the needle for performance rather than just doing PAO for PAO sake.

I’m not saying PAO is bad thing by any means. I’m just saying that the cost premium is only justified in a handful of applications, niche roles that don’t apply to most street driver cars where a -40 pour points is sufficient. I’d much rather the cost premium be spent on some Esterex, Synnestic, and Molyvan than on upgrading the base to PAO.

Great post, and yes, I agree and am aware of the PCMO being by far the best bang-for-the-buck oil available today. In the right vehicle with the correct driving profile, it’s possible to get this oil down into the ~$4-5/quart range based on OCI’s. One of HPL’s fleet customers with over 12,000 vehicles (3.5 EB’s no less!) runs the PCMO in 15-20k OCIs in service more brutal than any of us would willingly submit our favorite vehicles to…. Including HUNDREDS of hours of idling.

I probably won’t mess with the oil heat exchanger, even though there’s no easy way to see coolant temp vs oil temp. I think for now, I’ll continue with the ~7-8k OCIs on PCMO, and try to schedule a weekly high-temp run to keep the fuel down. PCMO is obviously doing a great job especially for the $. Only downside is the wife won’t let me put the 2’x4’ HPL sticker on her back window!

 

[SubieRubyRoo]

If you remove the 4.8% fuel, the KV100 becomes 10.1 cSt.

When factoring the approximate distillation curve for E10 pump gas, the difference between 180°F oil temp and 220°F oil temp would be +/-0.35% fuel dilution. It shouldn't make much difference.

Regular 87 E10 pump gas

IBP - 95°F
5% - 118°F
10% - 128°F
20% - 139°F
30% - 148°F
40% - 155°F
50% - 198°F
60% - 233°F
70% - 257°F
80% - 282°F
90% - 318°F
95% - 338°F
FBP - 386°F

Love your insightful posts, Bryce. Going deeper than what most people think, to bring out the true concerns (or lack thereof).

However, your post got me thinking… TGDI engines are generally tuned “rich” at low RPM to help quench potential LSPI events, right? So it may not be so much the oil temp causing dilution, but the ECM/TCM commanding a low CVT ratio for economy at low throttle inputs could be a big contributor to dilution?

Lots of low RPM fueling, combined with the inherent Boxer inefficiency at low RPMs… could lead to a much higher % of fuel ending up as liquid vs vapor under typical driving conditions. Maybe this is why the ~10% mileage in this OCI kept manually above 3k RPM has resulted in the lowest fuel dilution to date? Higher airspeed, lots more overall air volume, and less time for fuel to condense on the cylinder wall and be scraped into the crankcase?

 

[RDY4WAR]

Love your insightful posts, Bryce. Going deeper than what most people think, to bring out the true concerns (or lack thereof).

However, your post got me thinking… TGDI engines are generally tuned “rich” at low RPM to help quench potential LSPI events, right? So it may not be so much the oil temp causing dilution, but the ECM/TCM commanding a low CVT ratio for economy at low throttle inputs could be a big contributor to dilution?

Lots of low RPM fueling, combined with the inherent Boxer inefficiency at low RPMs… could lead to a much higher % of fuel ending up as liquid vs vapor under typical driving conditions. Maybe this is why the ~10% mileage in this OCI kept manually above 3k RPM has resulted in the lowest fuel dilution to date? Higher airspeed, lots more overall air volume, and less time for fuel to condense on the cylinder wall and be scraped into the crankcase?

That is a legitimate theory. The majority of fuel dilution will happen during warmup when the air/fuel ratio is richer, timing is later, and cylinder/chamber temperature is too low to vaporize the fuel well.

 

[Highboy]

Great post, and yes, I agree and am aware of the PCMO being by far the best bang-for-the-buck oil available today. In the right vehicle with the correct driving profile, it’s possible to get this oil down into the ~$4-5/quart range based on OCI’s. One of HPL’s fleet customers with over 12,000 vehicles (3.5 EB’s no less!) runs the PCMO in 15-20k OCIs in service more brutal than any of us would willingly submit our favorite vehicles to…. Including HUNDREDS of hours of idling.

I probably won’t mess with the oil heat exchanger, even though there’s no easy way to see coolant temp vs oil temp. I think for now, I’ll continue with the ~7-8k OCIs on PCMO, and try to schedule a weekly high-temp run to keep the fuel down. PCMO is obviously doing a great job especially for the $. Only downside is the wife won’t let me put the 2’x4’ HPL sticker on her back window!

You could get a ScanGauge3 and watch water,oil and CVT temperatures.

 

[SubieRubyRoo]

You could get a ScanGauge3 and watch water,oil and CVT temperatures.View attachment 310221

Cost? If it’s where I’m thinking, I’d rather just buy a Cobb AccessPort and do 2-for-1…

 

[Highboy]

Cost? If it’s where I’m thinking, I’d rather just buy a Cobb AccessPort and do 2-for-1…

https://www.scangauge.com/products/productsscangauge-iii/

 

[mt23]

Cost? If it’s where I’m thinking, I’d rather just buy a Cobb AccessPort and do 2-for-1…

the scangauge 2 works very well too. ~$150

 

[FZ1]

Welp, after some USPS shenanigans, WearCheck finally received my sample from October 11th on November 7th. Good thing I put it in a Priority flat rate envelope; if I had shipped it ground WearCheck may not have gotten it until Easter 2027!

Anyways, fuel is down and here’s my theory: wife’s daily commute of 14 miles, combined with the serious oil cooler mean even in summertime the oil never gets over maybe 186-187*. So my plan of attack this OCI was that every time I drove it, I would run the CVT manually and maintain ~3k RPM and about 62mph until the oil was 212*+ for at least 15 miles or until I got home. Unfortunately for the last 2-3 weeks of this OCI I was unable to get the oil hot and I think that’s part of the reason fuel was still 4.8%.

Considering iron is just above 1ppm with ~5% fuel and probably 10-12% of this OCI at 3k+ RPM, shows even the “base” @High Performance Lubricants oil is robust. Viscosity is down just a touch, for obvious reasons but since this engine specs a 0w20, there’s still plenty of safety net here.

To my final part: I’m actually considering removing the oil cooler and replacing the two hoses with a single piece so that it just loops around since the cooler is too good at its job. Heck, even on a 850+ mile trip this summer with the trunk full and the Speedo between 75-80mph, the oil was only 205-207*F.

Am I crazy for thinking of removing the oil cooler?

On to the report!
View attachment 310077View attachment 310078

If, it ain't Broke don't "Fix" it.

 

[TiGeo]

Considering the OEM recommends 20 grade, I don’t care one bit about ending viscosity at 8.7.

Besides, the oil cooler is on the top of the engine, right under the oil filter. Not sure why you’re so averse to oil running at 212* or above, especially an oil as robust as this?

Because now it's going to take longer to get your oil up to temp so you will be running the oil at a lower temp for longer without the heat exchanger. You would be better off trying to run a higher temp thermostat if that's even possible.

 

[bluesubie]

I think the solution for lower fuel is to switch to Blackstone. The lower fuel results will put your mind at ease.

 

[SubieRubyRoo]

Because now it's going to take longer to get your oil up to temp so you will be running the oil at a lower temp for longer without the heat exchanger. You would be better off trying to run a higher temp thermostat if that's even possible.

Have to see where actual temp is first. Dummy gauge doesn’t have any indication. Middle is halfway between “meat locker” and “your engine is now molten lava”

 

[buster]

Subaru's show low wear on any oil and we know used oil analysis are limited. Everything looks fine. Nitration is creeping up but you're not at an abnormal level yet (+17 over baseline is elevated). Oxidation is ok. Viscosity drop is expected due to the high fuel dilution. Strong TBN as usual for HPL. Not sure how meaningful that is due to the conflicting debate on TBN relevance.

ZR2 has the same issue. Runs too cool. I will lock out gears 5-8 often to run rpms at a sustained 3k for a period of time in hope of getting the oil warmer.

 

[buster]

@SubieRubyRoo your HPL is keeping iron under 1.5ppm/1K miles even as dilution creeps up near 5%. That’s some very impressive performance if you ask me. I’m thinking many oils struggle to keep it under 2ppm/1k even with next to no diliution. The few that can certainly aren’t doing it in a Subaru!

And the undiluted KV100 of 10.1 per @RDY4WAR calculation shows that your 5w-30 sheared almost nothing in 7k miles. The dilution is the entire source of KV100 loss, or nearly so.


IN sidebar and offline discussions, I’ve begun making the argument that HPL’s barebones PCMO is an absolutely killer oil for the money, and is the real star of the HPL line. The upgrades to base and VII in the other main lines are upgrades most people do not need or benefit from except in specialty duty cycles. HPL wisely makes PCMO robust by spending the money on the co-bases, add packs and top treat. That’s what separates basic PCMO from a typical group III and why I think that basic PCMO is a heck of a deal. It is supremely intelligently engineered in terms of value, spending the money on what moves the needle for performance rather than just doing PAO for PAO sake.

I’m not saying PAO is bad thing by any means. I’m just saying that the cost premium is only justified in a handful of applications, niche roles that don’t apply to most street driver cars where a -40 pour points is sufficient. I’d much rather the cost premium be spent on some Esterex, Synnestic, and Molyvan than on upgrading the base to PAO.

Numerous Subaru used oil analysis all showing low wear regardless of oil.

3% fuel dilution, 3k miles.

S

Thread '2023 Subaru Outback XT FA24F; Mobil 1 0w20 / 0w30 mix ; 3189mi'

Nov 13, 2025

Oil report for my new-to-me 2023 Outback, this was a 50/50 mix of ESP 0w20 and 0w30. The intent was to get a viscosity that would dilute/shear to into 20 grade instead of below like a lot of other oils have seemed to do over on the outback forums within 3k miles. The car is mostly used for kid hauling/grocery getting so not a ton of longer trips/highway miles. This oil was in service for approximately 4 months. This came out and straight ESP 0w30 went in, decided to stop trying to play backyard chemist. For the next interval, I feel confident in running it for a full 6 months or 6k miles...

• sac240
• Replies: 19
• Forum: Used Oil Analysis - Gasoline

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