Oil Cooler/Reliability Mods

[CSG Mike]

Band-aiding pressures with thicker oil is strictly that: a band-aid.

As a general rule, I consider anything over 240F on the higher side, and over 260F questionable, unless known normal (e.g. S2k). Even on the known normal, oil coolers are proven to reduce wear.

[ZDan]

Originally Posted by CSG Mike

Band-aiding pressures with thicker oil is strictly that: a band-aid.

Sometimes a band-aid makes more sense than a full-body cast!

Downsides to running 0W or 5W, 30- or 40-weight synthetic during warm track-season months are pretty much nonexistent...

As a general rule, I consider anything over 240F on the higher side, and over 260F questionable, unless known normal (e.g. S2k).

Others consider 260F to be a reasonably prudent limit for *conventional* oil.
Good synthetic oil is widely considered to be fine up to at least 300F.

oil coolers are proven to reduce wear.

I haven't seen anything conclusive on this, kind of a hard thing to prove...
Two identical FT86s running identical street/track usage running the same 0w20 oil, yeah, I'd bet the one with an oil cooler would exhibit less engine wear. But compensating with heavier oil in the non-oil-cooler car to achieve same viscosity at track operating temp as car with oil cooler, seems like wear rates should be similar.

[TommyW]

Heat in relation to an engine goes past just oil temps. More heat than necessary in the engine bay is never a good thing. A cooler running motor (to a point) is just a lot happier. I don't think I've ever seen someone after a session attempt to get the engine bay hotter, hence opening up the hood to cool things down.

[ZDan]

Originally Posted by TommyW

Heat in relation to an engine goes past just oil temps. More heat than necessary in the engine bay is never a good thing. A cooler running motor (to a point) is just a lot happier. I don't think I've ever seen someone after a session attempt to get the engine bay hotter, hence opening up the hood to cool things down.

Engine bay temp is more related to coolant temp than oil temp.

Seems like adding an oil cooler could *increase* engine bay temps, no?

[Petah78]

Originally Posted by Dzmitry

Not sure you're making the proper correlation. An oil cooler keeps temperatures from getting above "optimal"... for the most part. The oil temperature is what affects the oil pressure. The same oil would not run 40psi at 230F and also at 270F. Pressures at the higher temperature would be lower due to the oil having a lower viscosity.

As ZDan suggested, my comparison is that adding an oil cooler actually lowers oil pressure thus negating the benefits of the cooler. So the question still stand, is the effect of oil pressure of 40psi the same @ 230f or 270f? Or will a hotter oil "protect/lubricate" less at a higher temp?

Originally Posted by Dzmitry

The main concept that people try to convey with this platform is that our oil temperatures get too high easily, causing oil pressure to drop. Recall Savagegeese's data from tracking:
"
0w20 Redline 185F @ 800RPM 10PSI Oil Pressure
0w20 Redline 185F @ 2000RPM 35PSI Oil Pressure
0w20 Redline 185F @ 4000RPM 54PSI Oil Pressure
0w20 Redline 185F @ 7000RPM 65PSI Oil Pressure

0w20 Redline 225F @ 800RPM 7PSI Oil Pressure
0w20 Redline 225F @ 2000RPM 30PSI Oil Pressure
0w20 Redline 225F @ 4000RPM 48PSI Oil Pressure
0w20 Redline 225F @ 7000RPM 43PSI Oil Pressure
"
Though this data doesn't paste the whole picture, it gets the general idea across. So to answer your question, adding an oil cooler would bring the temperatures back down to say "185F" and provide you with proper oil pressure at desired RPM.

EDIT: To add to this, the data you posted does make it difficult to see the benefit, which is where some question an oil cooler. This is because at such high temperatures, there should be very minimal changes in pressure. I think what it comes down to more is an oil cooler is designed to keep your temperatures from ever getting up to the area where pressures start to even out (~240-280F+). But then nor is it ideal for the oil temps to be sitting at 170F as pressures are double-triple of what we would like. But this would only be an issue for those who mostly use their car for DD and don't ever see optimal or high temps at all.

Looking at the chart, with the oil cooler and 5W-30 (green lines), you are spending more time below the redline (10psi/1k rpm) threshold for daily/spirited driving (up to 240f) than without cooler (yellow lines).


And I always hear that the 1k rpm/10psi pressure rule of thumb, but if I understand oil pressure correctly, flow is not fully reflected in this reading (again, please correct me if i am wrong). You can have optimal pressure with very little flow which can lead to bad things as well. From my reading, even if you add an oil cooler, use heavier oil etc, you are still not achieving "optimal" pressures. Despite my efforts, I can't find any documentation for "optimal" oil pressure for the FA under track driving conditions. Is 40ish psi good enough? Or was it a design flaw?

[dragoontwo]

Originally Posted by Petah78

As ZDan suggested, my comparison is that adding an oil cooler actually lowers oil pressure thus negating the benefits of the cooler. So the question still stand, is the effect of oil pressure of 40psi the same @ 230f or 270f? Or will a hotter oil "protect/lubricate" less at a higher temp?



Looking at the chart, with the oil cooler and 5W-30 (green lines), you are spending more time below the redline (10psi/1k rpm) threshold for daily/spirited driving (up to 240f) than without cooler (yellow lines).


And I always hear that the 1k rpm/10psi pressure rule of thumb, but if I understand oil pressure correctly, flow is not fully reflected in this reading (again, please correct me if i am wrong). You can have optimal pressure with very little flow which can lead to bad things as well. From my reading, even if you add an oil cooler, use heavier oil etc, you are still not achieving "optimal" pressures. Despite my efforts, I can't find any documentation for "optimal" oil pressure for the FA under track driving conditions. Is 40ish psi good enough? Or was it a design flaw?

I don't think it's a heat issue in regards to lubrication or protection. It's a pressure issue as far as having a correct oil cushion in the rotating parts.

Eta- As you rev higher, you want a firmer cushion so parts don't contact each other while they whip around. At least, that's how I see it. Lower temps = better pressure.

[ZDan]

Originally Posted by dragoontwo

I don't think it's a heat issue in regards to lubrication or protection. It's a pressure issue as far as having a correct oil cushion in the rotating parts.

Eta- As you rev higher, you want a firmer cushion so parts don't contact each other while they whip around. At least, that's how I see it. Lower temps = better pressure.

What the data shows is the *same* oil pressure with 5w30 at 270+F without an oil cooler, and at 250F with an oil cooler. About 7.5psi/1000rpm, or 52.5psi at 7000rpm.

[Dzmitry]

Originally Posted by Petah78

As ZDan suggested, my comparison is that adding an oil cooler actually lowers oil pressure thus negating the benefits of the cooler. So the question still stand, is the effect of oil pressure of 40psi the same @ 230f or 270f? Or will a hotter oil "protect/lubricate" less at a higher temp?

Looking at the chart, with the oil cooler and 5W-30 (green lines), you are spending more time below the redline (10psi/1k rpm) threshold for daily/spirited driving (up to 240f) than without cooler (yellow lines).

And I always hear that the 1k rpm/10psi pressure rule of thumb, but if I understand oil pressure correctly, flow is not fully reflected in this reading (again, please correct me if i am wrong). You can have optimal pressure with very little flow which can lead to bad things as well. From my reading, even if you add an oil cooler, use heavier oil etc, you are still not achieving "optimal" pressures. Despite my efforts, I can't find any documentation for "optimal" oil pressure for the FA under track driving conditions. Is 40ish psi good enough? Or was it a design flaw?

True, I kind of missed this important point of an oil cooler lowering oil pressure. In that case, the effect SHOULD be different. Because viscosity of the oil will be different, but the pressure remains the same, the oil at 230F will flow at the same pressure as the one at 270F, but thinner (i.e. likely worse for proper lubrication, but I have nothing to back that statement up other than general understanding of how oil flows at different viscosities and pressures).

You make a good point about this being a negative effect on DD, which I fully agree with, hence why I am pretty firm in believing a DD should not have the need for an oil cooler. A simple bump up in oil weight (band-aid) should do enough for any minor temperature increases.

So the 10 psi per 1k RPM rule is simply that... a general rule made up a long time ago (kind of like an average for most vehicles). This certainly doesn't reflect accurately to all vehicles and for some it is probably quite off. Someone has posted on the forum several times what our platform recommends as the standard pressure per RPM from the manual, and it is pretty close to that rule if I recall. I will see if I can dig it up. But the idea is simple of course, you would try to match the pressure that you car recommends, because the engineers that designed the engine probably know what is best for it in terms of good oil flow. But... this is likely strictly speaking in the perfect world of using the oil recommended, and no other upgrades such as oil coolers. I do believe changing oil weight is a safe way to adjust oil pressure to keep it flowing properly. An oil cooler on the other hand... may be a different story. As ZDan and you pointed out, it changes the characteristics of the flow by reducing pressures.

EDIT: Ok, so after searching for a while I finally found the little bit of info the manual offers in terms of oil pressure for our platform. This has been posted on the forum a few times in the past.
https://www.subarucar.net/sites/suba...FA20D_DOHC.pdf
It only offers one piece of information: At 80C, pressures should be greater than 7.3psi at idle and greater than 73psi at 6k RPM.

[Petah78]

Originally Posted by Dzmitry

True, I kind of missed this important point of an oil cooler lowering oil pressure. In that case, the effect SHOULD be different. Because viscosity of the oil will be different, but the pressure remains the same, the oil at 230F will flow at the same pressure as the one at 270F, but thinner (i.e. likely worse for proper lubrication, but I have nothing to back that statement up other than general understanding of how oil flows at different viscosities and pressures).

I would agree as well. The "thicker" oil (230f, less thinned out) should provide more film strength to prevent metal to metal contact. However, I am not an engineer so i can't be 100% certain. If I am correct though, I rather have optimum file strength AND pressure for 99% of my driving (DD/Spirited) than "better" film strength when I am on track (1% of my driving).

Originally Posted by Dzmitry

You make a good point about this being a negative effect on DD, which I fully agree with, hence why I am pretty firm in believing a DD should not have the need for an oil cooler. A simple bump up in oil weight (band-aid) should do enough for any minor temperature increases.

From the data that i have seen, there are absolutely no reasons for an oil cooler for DD/spirited cars. For frequently or dedicated track cars, i think an oil cooler is probably a smarter way to go. The only debate is for cars that are lightly tracked DDs which is what my car is. I am leaning towards no cooler as well.

Originally Posted by Dzmitry

So the 10 psi per 1k RPM rule is simply that... a general rule made up a long time ago (kind of like an average for most vehicles). This certainly doesn't reflect accurately to all vehicles and for some it is probably quite off. Someone has posted on the forum several times what our platform recommends as the standard pressure per RPM from the manual, and it is pretty close to that rule if I recall. I will see if I can dig it up. But the idea is simple of course, you would try to match the pressure that you car recommends, because the engineers that designed the engine probably know what is best for it in terms of good oil flow. But... this is likely strictly speaking in the perfect world of using the oil recommended, and no other upgrades such as oil coolers. I do believe changing oil weight is a safe way to adjust oil pressure to keep it flowing properly. An oil cooler on the other hand... may be a different story. As ZDan and you pointed out, it changes the characteristics of the flow by reducing pressures.
EDIT: Ok, so after searching for a while I finally found the little bit of info the manual offers in terms of oil pressure for our platform. This has been posted on the forum a few times in the past.

Originally Posted by Dzmitry

https://www.subarucar.net/sites/subarucar.net/files/FA20D_DOHC.pdf
It only offers one piece of information: At 80C, pressures should be greater than 7.3psi at idle and greater than 73psi at 6k RPM.

A couple additional things that i have noted from my research:

1. Any engine that are tracked will see elevated oil temps. 280f is not uncommon for even Honda B-series, F-series or even the K-series and and oil pressure for these engines also drop as oil temp climbs. I think i read about 60psi for a F-series engine at redline. Adding oil cooler to these applications also reduces oil pressure.

2. Bigger engines with more pistons/displacement will run hotter than 4 cycl. But that is just basic physics with more pistons generating heat. I have read that corvette boots around town at 230f and can see well over 300f during track conditions. I believe they are just spec'd normal M1 5/10W-30. This makes our 270f looking pretty good in comparison. So what is "too" hot?

3. To add to the complexity, we have not even discussed "oil flow" in this equation. Adequate pressure doesn't mean a whole lot without proper flow. You need an adequate supply of oil in order to provide proper lubrication. I remember coming across an article where it stated the FI version of the FA20 oil pump has a ridiculously high flow rate (though i can't remember the exact metric). However, i never found any specs for the NA version of the FA20. And our oil pumps are positive displacement meaning the flow is fixed.

All this to say is that all engines are designed differently so how can we apply the "1k/10psi" threshold as a general guideline? Is the 40ish PSI of oil pressure at 270f PROVEN to be a problem for a leisurely tracked FA? Will it yield appreciable wear that will make a tangible difference in your ownership of the car?

[ZDan]

Originally Posted by Dzmitry

True, I kind of missed this important point of an oil cooler lowering oil pressure. In that case, the effect SHOULD be different. Because viscosity of the oil will be different, but the pressure remains the same, the oil at 230F will flow at the same pressure as the one at 270F, but thinner (i.e. likely worse for proper lubrication, but I have nothing to back that statement up other than general understanding of how oil flows at different viscosities and pressures).

Of course you don't want the oil to get too thin, which is why I run 5W30 during track-season.

You make a good point about this being a negative effect on DD, which I fully agree with, hence why I am pretty firm in believing a DD should not have the need for an oil cooler. A simple bump up in oil weight (band-aid) should do enough for any minor temperature increases.

The manual states that higher-viscosity oils may be used in hotter climates or under hard usage, and 0W20 is specified for normal usage for reasons other than maximum engine durability anyway. I don't consider 30wt a "band-aid", it's just logical to run thicker oil than 20wt at the track even if you have an oil cooler. From the data we've been looking at, without a cooler oil temps get up to ~275F, and with a cooler ~250F. Here's a viscosity vs. temperature for 0w20, 5w30 RC (resource conserving), 5w30 HD (heavy duty), 5w40, and 10w50:


Above 270F, 0w20 is below 5 cSt. So, get a cooler that puts you at 250F at the track, with 0w20 that'd put you ~6 cSt. Same viscosity as "normal" resource-conserving 5w30 at ~270-275F without the cooler.

Ok, so after searching for a while I finally found the little bit of info the manual offers in terms of oil pressure for our platform. This has been posted on the forum a few times in the past.
https://www.subarucar.net/sites/suba...FA20D_DOHC.pdf
It only offers one piece of information: At 80C, pressures should be greater than 7.3psi at idle and greater than 73psi at 6k RPM.

Important to note that this is not saying that 73psi is a *requirement*. It's only saying that less than 73psi at 6000rpm *at 80C (176F)* might indicate a problem. Of course at higher temps pressure will be lower.

[TylerLieberman]

I only have a GReddy oil cooler and Radium catch can on my car for "reliability". Stock NA.

Catch can is obviously not a requirement, but typically opt to run them on cars to monitor blow by levels and limit/reduce them, since it can contribute to increased knock. Not so much an issue with these cars; especially stock/NA.. but extra peace of mind for me.

The cooler seems like a no brainer to me, honestly. Here in AZ, I would get upt 230-240F oil temps just cruising down the highway @75mph in the summer, when ambient temps are passing 110º.

I could only imagine how fast oil temps would get up even further on track in similar conditions. With the GReddy cooler, I was able to go through a full track day at ~105º ambient temps, with the oil never surpassing 230-240. I would go for a good 4-5 laps, then do a cool down, and do another 3 or 4 before the final cool down into the pits.

I'm sure some people can "get away" without having one, but I personally don't want to "get away" with anything lol. I want to know that the car has what it needs to be reliable. Plus, it sucks going to an event and only being able to do 1-2 laps before running into temp issues. That's what I had to deal with on my STI during summer events, where the car would do 2 laps around AutoClub Speedway and then I'd start seeing high oil/water temps and I'd have to do 1-2 cool down laps before the temps were acceptable again. So I'd get like 4 hot laps per 20 minute session. Lame AF. And that was STILL in sub 100º weather.

[Dzmitry]

Originally Posted by TylerLieberman

I only have a GReddy oil cooler and Radium catch can on my car for "reliability". Stock NA.

Catch can is obviously not a requirement, but typically opt to run them on cars to monitor blow by levels and limit/reduce them, since it can contribute to increased knock. Not so much an issue with these cars; especially stock/NA.. but extra peace of mind for me.

The cooler seems like a no brainer to me, honestly. Here in AZ, I would get upt 230-240F oil temps just cruising down the highway @75mph in the summer, when ambient temps are passing 110º.

I could only imagine how fast oil temps would get up even further on track in similar conditions. With the GReddy cooler, I was able to go through a full track day at ~105º ambient temps, with the oil never surpassing 230-240. I would go for a good 4-5 laps, then do a cool down, and do another 3 or 4 before the final cool down into the pits.

I'm sure some people can "get away" without having one, but I personally don't want to "get away" with anything lol. I want to know that the car has what it needs to be reliable. Plus, it sucks going to an event and only being able to do 1-2 laps before running into temp issues. That's what I had to deal with on my STI during summer events, where the car would do 2 laps around AutoClub Speedway and then I'd start seeing high oil/water temps and I'd have to do 1-2 cool down laps before the temps were acceptable again. So I'd get like 4 hot laps per 20 minute session. Lame AF. And that was STILL in sub 100º weather.

I think the main point of this discussion is that an oil cooler is not a "no brainer" and has no solid proof of benefiting the platform under DD or light track use. In any case, to each their own.

[Dzmitry]

Originally Posted by Petah78

I would agree as well. The "thicker" oil (230f, less thinned out) should provide more film strength to prevent metal to metal contact. However, I am not an engineer so i can't be 100% certain. If I am correct though, I rather have optimum file strength AND pressure for 99% of my driving (DD/Spirited) than "better" film strength when I am on track (1% of my driving).



From the data that i have seen, there are absolutely no reasons for an oil cooler for DD/spirited cars. For frequently or dedicated track cars, i think an oil cooler is probably a smarter way to go. The only debate is for cars that are lightly tracked DDs which is what my car is. I am leaning towards no cooler as well.



A couple additional things that i have noted from my research:

1. Any engine that are tracked will see elevated oil temps. 280f is not uncommon for even Honda B-series, F-series or even the K-series and and oil pressure for these engines also drop as oil temp climbs. I think i read about 60psi for a F-series engine at redline. Adding oil cooler to these applications also reduces oil pressure.

2. Bigger engines with more pistons/displacement will run hotter than 4 cycl. But that is just basic physics with more pistons generating heat. I have read that corvette boots around town at 230f and can see well over 300f during track conditions. I believe they are just spec'd normal M1 5/10W-30. This makes our 270f looking pretty good in comparison. So what is "too" hot?

3. To add to the complexity, we have not even discussed "oil flow" in this equation. Adequate pressure doesn't mean a whole lot without proper flow. You need an adequate supply of oil in order to provide proper lubrication. I remember coming across an article where it stated the FI version of the FA20 oil pump has a ridiculously high flow rate (though i can't remember the exact metric). However, i never found any specs for the NA version of the FA20. And our oil pumps are positive displacement meaning the flow is fixed.

All this to say is that all engines are designed differently so how can we apply the "1k/10psi" threshold as a general guideline? Is the 40ish PSI of oil pressure at 270f PROVEN to be a problem for a leisurely tracked FA? Will it yield appreciable wear that will make a tangible difference in your ownership of the car?

Yes, getting into oil flow becomes very complex. But to finish off, I am not trying to apply the 1k/10psi rule as a general guideline, I simply see it partially working with our platform based on the manual specs for psi at 80C. But, as noted, it's extremely limited and nothing but assumptions can be made off of this information.

I think the question shouldn't be whether 40psi of oil at 270F is a problem for a leisurely tracked FA, but rather is it bad in general to have 40psi at high RPM. Based on how oil flow works and how engineers typically spec pressures to rise for higher RPM's, I would like to believe there is some negative to it. How much is another story.

[Dzmitry]

Originally Posted by ZDan

Of course you don't want the oil to get too thin, which is why I run 5W30 during track-season.


The manual states that higher-viscosity oils may be used in hotter climates or under hard usage, and 0W20 is specified for normal usage for reasons other than maximum engine durability anyway. I don't consider 30wt a "band-aid", it's just logical to run thicker oil than 20wt at the track even if you have an oil cooler. From the data we've been looking at, without a cooler oil temps get up to ~275F, and with a cooler ~250F. Here's a viscosity vs. temperature for 0w20, 5w30 RC (resource conserving), 5w30 HD (heavy duty), 5w40, and 10w50:


Above 270F, 0w20 is below 5 cSt. So, get a cooler that puts you at 250F at the track, with 0w20 that'd put you ~6 cSt. Same viscosity as "normal" resource-conserving 5w30 at ~270-275F without the cooler.



Important to note that this is not saying that 73psi is a *requirement*. It's only saying that less than 73psi at 6000rpm *at 80C (176F)* might indicate a problem. Of course at higher temps pressure will be lower.

Agreed, it is a very specific "requirement" based on a specific temperature. Obviously, we would expect this to adjust with rising temperatures. I believe pressures should remain somewhat linear with the change though. In other words, if we have 6 psi at idle at some higher temperature, we should probably have 60psi at 6k RPM at the same temperature. That's really all that freaks people out with this platform, is this drop in oil pressure right near the peak RPM range unexpectedly. I am sure if pressures were fairly linear, this subject would probably lack much existence with these cars, regardless of higher temperatures. So to fix the problem, most people decided an oil cooler is the way (contrary to my belief, but who knows).