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22' Crosstrek 6MT
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Discussion Starter · #1 ·
Hi everyone,

First time poster and owner of a 22’ Crosstrek 6MT. I wanted to share a personal conversation I had with my local dealer, as well as information I’ve gathered from several sources regarding oil fill level, oil temperature, and oil pressure. I’m sharing this info to potentially dispel some common myths and theories I read in our community and to simply start a fun conversation. I know this is a dense post, but I’ve tried to highlight the topics and key findings.

Oil Fill level: Like many of us, my Crosstrek came from the factory with what I estimated to be roughly 5.3-5.5 quarts in the crankcase. The oil level on the dipstick was .5” above the full dot. This was based off a cold engine on a level surface and was repeatable over several days. This prompted me to make several phone calls to different dealerships where I received numerous answers regarding the factory fill amount. My local dealership told me 5.3 quarts was the factory fill on my car according to Subaru of America. That answer was consistent with the oil level I saw on the dipstick when I took ownership of the car. The owner’s manual that came with my car states that the proper oil fill with oil filter change is 4.7 quarts. When I completed the first oil change, I measured out 4.7 quarts for the fill. Under identical conditions as stated above, 4.7 quarts in the crankcase puts the oil level about a .25” below the full dot. This result was repeatable over several days.

We’ve all debated over why Subaru seemingly “overfills” the Crosstrek’s (Oil consumption, long drain intervals, etc.). I’m proposing that more oil in the crankcase is not always a good thing and may be hindering engine performance, extending the time the engine oil is under operating temperature, and may play a role in the decline of engine oil pressure at higher RPMs.

Engine Oil Temperature: When I initially thought through the pros and cons of running more oil in the car, I thought of oil temperature. Luckily, our cars have an oil temperature sensor which a scan tool with a smartphone interface can display this metric while you drive. Under normal driving conditions in moderate weather, I find the oil temperature to settle in around 200-210 degrees fahrenheit. Over the summer, I saw oil temperatures as high as 235 degrees while climbing a grade in 100-degree heat. I’ve found reputable sources that state synthetic engine oil that complies with modern SAE standards (API SP / ILSAC GF-6A) will withstand temperatures of over 300 degrees. I’ve also seen dyno testing that proved hot oil and cold coolant is the combo you want for performance and reliability. Water boils at 212 degrees. This would suggest that we want our engine oil to reach that temperature to evaporate the water in the crankcase caused by normal combustion. This led me to believe that overfilling our cars is increasing the length of time the oil is under ideal operating temperature (210-220). See video linked below for a more detailed explanation of the relationship between oil temperature and quantity.

Oil Pressure: As far as I can tell, our cars do not possess the ability to display a numeric oil pressure reading. Even through a scan tool (I will be looking into this more). This is a disappointment as oil pressure can be a valuable diagnostic tool when deciding how much oil to run in the car. A video created by Motor trend brings some invaluable information to light regarding how oil fill can both increase horsepower and oil pressure at the same time. Amazing! Those gentlemen were able to pick up 22 horsepower simply by running less oil in the sump. What was equally impressive was the increase in oil pressure and stability. They saw several more psi of oil pressure as well as a more linear curve under the same conditions. They attributed this to the decrease in windage in the crank case. If you’re not familiar, windage is the term used to describe the cloud of oil inside the crank case due to oil being flung off rotating parts such as the crank shaft. Running less oil in the sump, along with installing a baffled oil pan saw the improvements stated above. Windage is created in all internal combustion engines regardless of piston quantity and configuration (V8 vs. Boxer).

It was noted that these benefits in power and oil pressure were more pronounced at high RPM. Regardless, I felt these results were indicative of a fundamental myth that more oil is always better.

The drawback they identified to running less oil in the sump was the potential for oil to slosh away from the pick-up under hard breaking and cornering. Because the engine was mounted on a dyno, they were unable to incorporate this variable into their testing. I believe testing with a numeric oil pressure gauge would have to be conducted during real world driving conditions to rule out any unforeseen drops in oil pressure.

My conclusion: Assuming the oil dipstick is an accurate representation of the amount of oil the Subaru engineers designed being ran in our cars, I feel the data suggests that using 5 or more quarts during an oil change decreases engine output (horsepower) and potentially reduces engine oil pressure during high RPM driving conditions. I personally decided to try 4.5 quarts during my last oil change. I can report that this fill amount puts the oil level almost right in the middle of the high and low dots. It should also be noted that the manual claims that 1.1 quarts is the difference between the low and high dot. This tells me I could pull even more oil out. Maybe even down to 4 quarts.

I’d appreciate all constructive and thoughtful responses and opinions regarding this topic. Please see videos listed below.

Motor trend oil level testing:

Oil temperature / fill relationship:

Article regarding safe oil temperature: What Is The Optimum Engine Oil Temperature? - Hot Rod Magazine
 

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2022 Canadian Sport trim (6MT // 2.0 )
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Got to love well researched posts. Welcome to the forum!

Regarding oil overfill / temperature / horsepower. I would agree on the theory, but I would also argue that on a practical level it has little relevance, because
  • The "overfill" is roughly 10%. Thus, this is also how much longer it will take the oil to warm up. Instead of 10 min, it'll take 11, and instead of 20 min, it'll take 22.
  • Robbed "cold oil" horsepower. Yes but... you aren't supposed to floor it until you reach peak TQ/HP until the oil is warmed up anyways.
You've touched on one detail that I always wondered about - what is the maximum roll and pitch angle above which oil starvation could occur?

Interesting discussion, and you deserve the award of the first thread on oil which does NOT argue on which oil brand/weight (not) to use!!
 

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2021 Crosstrek Limited
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On my '21 Limited CVT, it was also overfilled by about the same amount as yours on the dipstick. Mine is supposed to take ~4.5 qts. They dumped a full 5 qts in, as when I changed it myself I also put the same 5qts in to see where the oil level would be. It was in the same place. If I put in 4.5qts it's a bit below full. 4.75qts gives me a hair above full. All checked when cold and sitting overnight.
 

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To make life simple I use dipstick. Regular oil change I will just filled with 4 litre oil, and the next day may be add 50cc to make it exact on the full mark dot. If I change the oil filter, I just put 4.2 litre oil and typically just leave it until next oil change. Engine warm up quick, oil and water temp is about 200 F, except I drive aggressively then the oil temperature may rise about 220 F with 95F ambient temperature. For Subaru I dont find much different on performance when oil is overfilled, but can feel performance drop on urban driving when switch to 30 weight.
 

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2018 Orange Subaru Crosstrek Limited
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Thanks for the interesting post. "Water boils at 212 degrees. This would suggest that we want our engine oil to reach that temperature to evaporate the water in the crankcase caused by normal combustion."
When you speak of the boiling point of water (at one atmosphere of pressure) you are describing a qualitative change but evaporation of water from the oil takes place at most temperatures and varies by how hot so it is quantitative. So a hot engine evaporates a lot of water, a warm engine is evaporating water but a cooler engine evaporates far less. In fact even at the boiling point there are places in the engine where the water may find to condense again. Small amounts of oil form a vapor cloud in the bottom end with the water/oil vapor floating around as well. Water condenses back into liquid and can be trapped within the oil. Your point, that cold temperatures can create more water contamination is generally true in any case but the boiling point of water isn't critical for this to happen. Short trips in cold weather can be tough on the oil and definitely are the most likely time for contamination.

As a mostly urban driver I worry about how available the oil in the pan is to my engine. On my soft road trips, especially when the vehicle is not level and going over deep potholes that worries me a bit as well especially when I am forced to drive very slowly at a sharp angle to get through some patch. Honestly I don't even know where the oil pick up is in the pan of a Subaru

My thoughts on overfilling the pan go mostly to screwing up contact points, o-rings and gaskets. It makes sense that windage is a factor in power and economy. My position is if you can't get the exact amount required in the pan then use slightly less until you are sure due to gaskets and such.

As far as getting an additional 22 horsepower increase from using less oil I'm skeptical of that. I'll check out your links more closely but even if true it doesn't answer the question of whether reduction of the oil volume might lead to a resultant increase in internal damage to the engine due to potential starvation. Since I'm not sure I don't think I'll try it although it was a fascinating thread and I thank you for that.
 

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That video showed a 22 HP loss on an engine making around 600 HP. So that would be like losing 5 HP on the Crosstrek. Every little bit helps, I guess.

And it’s also interesting to hear about the factory fills being high. Surely that’s no accident? There must be an automated system to put oil in each engine, so if they’re all overfilled, it must be intentional.
 

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2022 Crosstrek Limited
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Not just factory is overfilling our Subarus. Dealer oil changes get the full capacity too. At least 5 quarts. Maybe 5 liters. I pulled a half quart out after first dealer oil change. Level is still a 1/4” above the top dot.
I vacuumed some out on factory fill also.
I can live with oil level a 1/4” above full. An inch above no.
No one with Subaru explains why they consistory overfill the engine.
 

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Interesting.

all I know is that Gran Turismo games taught me that fresh oil adds 10 or more horsepower. and your car is more aerodynamic if you wash it.
Addtionally, car and motorcycle roadracers know that having the right stickers on their racing vehicles adds 5 mph to top-end speed.
 

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22' Crosstrek 6MT
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Discussion Starter · #10 ·
Got to love well researched posts. Welcome to the forum!

Regarding oil overfill / temperature / horsepower. I would agree on the theory, but I would also argue that on a practical level it has little relevance, because
  • The "overfill" is roughly 10%. Thus, this is also how much longer it will take the oil to warm up. Instead of 10 min, it'll take 11, and instead of 20 min, it'll take 22.
  • Robbed "cold oil" horsepower. Yes but... you aren't supposed to floor it until you reach peak TQ/HP until the oil is warmed up anyways.
You've touched on one detail that I always wondered about - what is the maximum roll and pitch angle above which oil starvation could occur?

Interesting discussion, and you deserve the award of the first thread on oil which does NOT argue on which oil brand/weight (not) to use!!
You bring up a good question regarding pitch angle. I'm not even sure where the pick-up is in the pan.
 

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22' Crosstrek 6MT
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Discussion Starter · #11 ·
Not just factory is overfilling our Subarus. Dealer oil changes get the full capacity too. At least 5 quarts. Maybe 5 liters. I pulled a half quart out after first dealer oil change. Level is still a 1/4” above the top dot.
I vacuumed some out on factory fill also.
I can live with oil level a 1/4” above full. An inch above no.
No one with Subaru explains why they consistory overfill the engine.
Seems to be common place. the service advisor at the dealership told me the fill amount is automated out of a machine. 5.3 quarts.
 

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Discussion Starter · #12 ·
On my '21 Limited CVT, it was also overfilled by about the same amount as yours on the dipstick. Mine is supposed to take ~4.5 qts. They dumped a full 5 qts in, as when I changed it myself I also put the same 5qts in to see where the oil level would be. It was in the same place. If I put in 4.5qts it's a bit below full. 4.75qts gives me a hair above full. All checked when cold and sitting overnight.
Who's to say the oil level must be at the full line? A healthy engine that isn't experiencing massive oil consumption may benefit from that reduction in windage I mentioned above. Good to know I'm not the only one experiencing the overfill.
 

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Discussion Starter · #13 ·
Thanks for the interesting post. "Water boils at 212 degrees. This would suggest that we want our engine oil to reach that temperature to evaporate the water in the crankcase caused by normal combustion."
When you speak of the boiling point of water (at one atmosphere of pressure) you are describing a qualitative change but evaporation of water from the oil takes place at most temperatures and varies by how hot so it is quantitative. So a hot engine evaporates a lot of water, a warm engine is evaporating water but a cooler engine evaporates far less. In fact even at the boiling point there are places in the engine where the water may find to condense again. Small amounts of oil form a vapor cloud in the bottom end with the water/oil vapor floating around as well. Water condenses back into liquid and can be trapped within the oil. Your point, that cold temperatures can create more water contamination is generally true in any case but the boiling point of water isn't critical for this to happen. Short trips in cold weather can be tough on the oil and definitely are the most likely time for contamination.

As a mostly urban driver I worry about how available the oil in the pan is to my engine. On my soft road trips, especially when the vehicle is not level and going over deep potholes that worries me a bit as well especially when I am forced to drive very slowly at a sharp angle to get through some patch. Honestly I don't even know where the oil pick up is in the pan of a Subaru

My thoughts on overfilling the pan go mostly to screwing up contact points, o-rings and gaskets. It makes sense that windage is a factor in power and economy. My position is if you can't get the exact amount required in the pan then use slightly less until you are sure due to gaskets and such.

As far as getting an additional 22 horsepower increase from using less oil I'm skeptical of that. I'll check out your links more closely but even if true it doesn't answer the question of whether reduction of the oil volume might lead to a resultant increase in internal damage to the engine due to potential starvation. Since I'm not sure I don't think I'll try it although it was a fascinating thread and I thank you for that.
That engine they were doing the testing on made almost 600 hp. The gain in power with our cars would be much less. I think you're spot on with the water contamination. That's what getting the oil up to temp is trying to reduce.
 

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Discussion Starter · #14 ·
That video showed a 22 HP loss on an engine making around 600 HP. So that would be like losing 5 HP on the Crosstrek. Every little bit helps, I guess.

And it’s also interesting to hear about the factory fills being high. Surely that’s no accident? There must be an automated system to put oil in each engine, so if they’re all overfilled, it must be intentional.
The service advisor told me the fill comes out of an automated machine and the quantity is set by Subaru.
 

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2022 Crosstrek Premium CVT
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I'd love to know why the initial factory fill is always more than what the manual calls for, mine certainly was. There must be a reason right? Because X amount overfill times so so many cars equals a good amount of money in oil. If there wasn't a reason, they wouldn't be doing this.
 

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I agree, just want to know why they initially overfill at the factory.
I can only speculate that an new engine that is completely void of oil may require a little more at the initial fill. This does not explain why a dealer may do the same as there is always some residual oil left in the engine after it's drained.

Doug
 

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2021 ISM Crosstrek Ltd
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Here is something from Subaru that shows another possible downside to overfilling the engine oil. Some years old and I’ve never seen it mentioned elsewhere… but…


From here, for context:
 
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