0w-30/5w-30 in a 2024 crosstrek and subaru timing chains

Glenda W. said:
Piston rings, excessive oil consumption, cylinder scoring, could lead to low oil pressure/engine failure.

https://static.nhtsa.gov/odi/rcl/2021/RCLRPT-21V259-6845.PDF
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I thought this thread was regarding the newer Smartstream engines. I am aware of that safety recall. I should - since I got one in my mailbox a couple years ago. I have that 2.0 NU MPI engine in our 2020 Kia and it was manufactured around May 2019. So it fits right in the middle of the alleged time-frame.

That's why I've been doing and continued to do 3k OCIs and the best motor oils popular on this website. I'm so glad I chose to abandon (after the very first oil change) the watery 5w20 synblends dealerships were pushing in 2020, 2021 and 2022.

If ours is part of that 1% failure rate, it will grenade in the next 5-10k mileage. I have 30k on ours and two others in my subdivision with the same engine and bought similar time, both grenaded before 35k. Only difference is they were running 5w20 syn blends and getting oil changes between 5-7.5k. I've been using 5/10w30 and 0w40 since that very first free dealership oil change at 3k. I removed that free oil change and replaced it about 1k later.

Female neighbor across the street has the 2023 Subaru Crosstrek. Her husband has the 2021 Kia Forte. Both are always parked out front and I have never seen the hood raised on either vehicle.
 
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Could a 30 weight cause a spun bearing or rod knock in an engine that’s spec’d/recommended for a 16 weight?
 
I don’t want to get into a pissing contest here. I don’t have data. The shop that used to build our race engines, in a conversation about engine oils and rings, said he would not use higher viscosity engine oils with low tension rings commonly used in modern engines chasing fuel economy. The higher viscosity could prevent the rings from seating properly (words to that effect) and oil consumption would result. I don’t believe that 0w30 or 5w30 would qualify as high viscosity engine oil. If under warranty, good luck getting assurances from the manufacturer that it is ok - look at my Subaru story from much earlier in the thread - the dealers don’t behave that way if someone isn’t checking. Make of it what you will. Have a good day.
 
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RAVL said:
I don’t want to get into a pissing contest here. I don’t have data. The shop that used to build our race engines, in a conversation about engine oils and rings, said he would not use higher viscosity engine oils with low tension rings commonly used in modern engines chasing fuel economy. The higher viscosity could prevent the rings from seating properly (words to that effect) and oil consumption would result. I don’t believe that 0w30 or 5w30 would qualify as high viscosity engine oil. If under warranty, good luck getting assurances from the manufacturer that it is ok - look at my Subaru story from much earlier in the thread - the dealers don’t behave that way if someone isn’t checking. Make of it what you will. Have a good day.
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Indeed.
 
RAVL said:
I don’t want to get into a pissing contest here. I don’t have data. The shop that used to build our race engines, in a conversation about engine oils and rings, said he would not use higher viscosity engine oils with low tension rings commonly used in modern engines chasing fuel economy. The higher viscosity could prevent the rings from seating properly (words to that effect) and oil consumption would result. I don’t believe that 0w30 or 5w30 would qualify as high viscosity engine oil. If under warranty, good luck getting assurances from the manufacturer that it is ok - look at my Subaru story from much earlier in the thread - the dealers don’t behave that way if someone isn’t checking. Make of it what you will. Have a good day.
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Wasn’t a contest here… just wanted to see if you had read a study that you could relay, or if it was word of mouth from third-hand, which is what I expected. All good, nothing personal.

I don’t think we’ve ever seen data here that shows heavier oils cause ring sealing issues, because the higher HT/HS should actually provide a better seal at the ring/cylinder wall interface because it can’t be “shoved” out of the way by the scraping effect of the ring, hence keeping the entire edge sealed up. It’s an interesting topic but if there is data confirming either theory, the people with the instrumentation and ability to measure this potential impact are keeping it close to the vest.
 
Subyrubyroo:

Good to hear. His point was that the space between the piston skirt and the bore on the new motors is tiny and the lower tension piston ring can get pushed out of the way. Same guy recommended 15w40 in the race engine he built for us so there was no “religion” on thick v thin as there is with some folks. When the motor is under warranty I have no idea why folks would diverge. The motors in most newer cars last almost forever with reasonable care, some crappy ones aside. It is the rest of the car that goes. As I said folks will make of it what they will.
 
RAVL said:
His point was that the space between the piston skirt and the bore on the new motors is tiny and the lower tension piston ring can get pushed out of the way.
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Clearances and their tolerances for piston skirts haven’t changed dramatically. Also, “lower tension” rings are generally thinner (as low as 1.0mm) which is where the majority of friction reduction comes in (and that data has been proven).

I may be off base, but I don’t believe there has been a major reduction in radial tension (how hard the ring presses against the bore); by simply reducing from a 5/32” ring to a 1.5mm ring resulted in a 50% reduction of the torque it took to turn over the engine. Besides, a thinner ring will have less surface area against the cylinder and also a higher proportion of “edge” vs “face”; all of these things combined lead me to believe thinner, low tension rings (that aren’t fluttering from crankcase pressure) have the potential to resist the “float” you’re talking about.

Again, it’s been years since I’ve been elbows-deep in cutting edge engines personally, but I’ve never seen or heard of the phenomena that was described to you.
 
Appreciate the productive and informative response. What I was told is that manufacturers have reduced piston to cylinder clearances for lower emissions. In the old days, they allowed for more piston expansion when the engine got hot. Now aluminum (silicon alloy) pistons do not have that degree of expansion when heated so that “fit” can be a lot tighter. Add low tension rings to reduce internal friction because you don’t need much tension to have a good seal given how precise and consistent (temp wise) the fits are - this is my translation of what was explained. This is all consistent with manufacturers being able to run thinner oils without impacting engine life. It is interesting to me that despite all the complaining we hear by some, myself included, the average age of a car is now like 12 years or similar. That’s the oldest it’s ever been. Cars and engines are lasting longer. Again appreciate the civil exchange. Take care.
SubieRubyRoo said:
Clearances and their tolerances for piston skirts haven’t changed dramatically. Also, “lower tension” rings are generally thinner (as low as 1.0mm) which is where the majority of friction reduction comes in (and that data has been proven).

I may be off base, but I don’t believe there has been a major reduction in radial tension (how hard the ring presses against the bore); by simply reducing from a 5/32” ring to a 1.5mm ring resulted in a 50% reduction of the torque it took to turn over the engine. Besides, a thinner ring will have less surface area against the cylinder and also a higher proportion of “edge” vs “face”; all of these things combined lead me to believe thinner, low tension rings (that aren’t fluttering from crankcase pressure) have the potential to resist the “float” you’re talking about.

Again, it’s been years since I’ve been elbows-deep in cutting edge engines personally, but I’ve never seen or heard of the phenomena that was described to you.
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Sometimes though I have to wonder just how large people think oil molecules are. And they imagine much greater viscosity differences between grades, especially when hot. In the scheme of things such as this it’s not that great. It’s significant and important but in terms of “squeezing in” the molecules it is not. Here we have a 30-grade as supposedly okay but a 40-grade is detrimental. There isn’t anything to support such a supposition.
 
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