Potential Cause of rumored GR86’s blown engine? Seal packing(RTV) was peeled off

[Ultramaroon]

Originally Posted by KillerBMotorsport

FSome call it a regulator, some call it a bypass. It's the same thing.

It does not open at 140psi.

Here's a plot showing oil pressure. Where the ramp rates change is where the bypass just cracks open and starts regulating. I would call it 75psi... which coincidentally, it right in line with 95% of the other oil pumps Subaru uses. The reason pressure keeps climbing after the bypass opens is because flow is increasing, further compressing the bypass spring, requiring more pressure to keep it open enough for the additional flow. Eventually what can happen is the bypass will aerate (if you have too big of a pump and an engine not made for it, for example), because flow out the bypass is horribly turbulent. Think of water coming out of a hose with your thumb covering the end. If you run too big of a pump AND shim it to increase pressure, then that inner rotor usually lives a short and violent life.

Flow is linear with RPM through the rotors (assuming constant temp and no AVCS). The bypass valve regulates the pressure and flow actually going into the engine.

I've read here that shimming the spring makes no difference. Also, with your mode of operation, especially considering the flow rate of the pump, it should compensate for viscosity (temp). It doesn't seem to.

[Petah78]

Originally Posted by KillerBMotorsport

^ correct. 2 gal/min is not a lot.

Sorry to be a noob but i am trying to understand. Are you suggesting that the dimensions of the pickup tube is limited oil flow of 2gal/min? Meaning that is the max that the engine is getting regardless how hard the oil is pumping? But if it's partially blocked, wouldn't that metric, 2gal/min be even lower?

[_____That_-_GUY_____]

Originally Posted by Petah78

Sorry to be a noob but i am trying to understand. Are you suggesting that the dimensions of the pickup tube is limited oil flow of 2gal/min? Meaning that is the max that the engine is getting regardless how hard the oil is pumping? But if it's partially blocked, wouldn't that metric, 2gal/min be even lower?

When the pump is at max PSI, it's only pushing 2 GPM through the engine, so that is all the pick up tube needs to pull from the oil pan. The tube with a partially blocked screen could most likely flow a lot more than that if it needed to, but the engine doesn't need more than that

[KillerBMotorsport]

Originally Posted by Ultramaroon

I've read here that shimming the spring makes no difference. Also, with your mode of operation, especially considering the flow rate of the pump, it should compensate for viscosity (temp). It doesn't seem to.

A shim doesn't do much. If you over-shim, it can actually cause pressure to be excessive and split the inner pump gear. I've heard of shims also causing premature bypass valve spring fatigue (from over compression). IMO, a shim is not beneficial beyond marginal.

Subaru oil pump are unusual in the car world in that they have WAY more flow than is necessary 95% of the time. There are V8 engines that don't have nearly as much oil flow capacity as a Suby pump. They've always been this way, and yet, they have (by design) poor rod bearing oiling and marginal main oiling

Here's a plot comparing the same pump with 2 shims added...

Originally Posted by Petah78

Sorry to be a noob but i am trying to understand. Are you suggesting that the dimensions of the pickup tube is limited oil flow of 2gal/min? Meaning that is the max that the engine is getting regardless how hard the oil is pumping? But if it's partially blocked, wouldn't that metric, 2gal/min be even lower?

Don't apologize, we've all been there!

No, not at all. From our testing the pickup is very little of a restriction when you look at the system as a whole. Can you pick up a couple psi and small % of flow by installing a performance high flow version, sure you can. Anytime you reduce a restriction on a pump's inlet, it becomes more efficient.

The systems flow limitations is really down to the engine's lubrication design: engine's clearances, and other things like AVCS, oil feed, etc... Those are all restrictive. The best way to improve oiling system performance is not by shimming or adding a bigger pump, it's rebuilding the engine with making modifications to the oiling system to improve its performance. One of the things we learned for example, is ALL engines (new used or otherwise) get a line bore (not a line hone). Once true, we actually close the main clearances below factory spec at ~.0007 +/-.0001. This smaller main clearance forces more oil to the rod bearings (the weak link). We've done this for stock engines running 0w20 to 760whp running 20w-60. We always run stock unshimmed pumps regardless or redline RPM or power level and have not had an oiling related failure in at least 10 years.

[Petah78]

Originally Posted by KillerBMotorsport

Don't apologize, we've all been there!

No, not at all. From our testing the pickup is very little of a restriction when you look at the system as a whole. Can you pick up a couple psi and small % of flow by installing a performance high flow version, sure you can. Anytime you reduce a restriction on a pump's inlet, it becomes more efficient.

The systems flow limitations is really down to the engine's lubrication design: engine's clearances, and other things like AVCS, oil feed, etc... Those are all restrictive. The best way to improve oiling system performance is not by shimming or adding a bigger pump, it's rebuilding the engine with making modifications to the oiling system to improve its performance. One of the things we learned for example, is ALL engines (new used or otherwise) get a line bore (not a line hone). Once true, we actually close the main clearances below factory spec at ~.0007 +/-.0001. This smaller main clearance forces more oil to the rod bearings (the weak link). We've done this for stock engines running 0w20 to 760whp running 20w-60. We always run stock unshimmed pumps regardless or redline RPM or power level and have not had an oiling related failure in at least 10 years.

That is some great explanation. The more I read/learn about this RTV/oiling issue, the more I think it's an overblown issue. Not ideal but also not a show stopper. Thanks again.

[BioRebel]

From the sounds of all this, it looks like this is only going to impact a small subset of cars. (ones with enough of a clogging issue and while they're being driven at the limit)


Honestly my only concern at this point is if this happens to me after the warranty expires.

[Dake]

Originally Posted by BioRebel

From the sounds of all this, it looks like this is only going to impact a small subset of cars. (ones with enough of a clogging issue and while they're being driven at the limit)

Honestly my only concern at this point is if this happens to me after the warranty expires.

And this should be a concern because for those that don't track it or otherwise drive aggressively, it could just take longer to see the internal damage manifest at which point it might be too late.

[Tcoat]

Originally Posted by Dake

And this should be a concern because for those that don't track it or otherwise drive aggressively, it could just take longer to see the internal damage manifest at which point it might be too late.

Or more likely they will never see any damage at all because they never hit that combination of factors to cause the perfect storm for it to happen.

Notice that the reports dropped off after the bulk of the cars got some miles on them?

[Petah78]

Originally Posted by BioRebel

From the sounds of all this, it looks like this is only going to impact a small subset of cars. (ones with enough of a clogging issue and while they're being driven at the limit)


Honestly my only concern at this point is if this happens to me after the warranty expires.

Just keep monitoring your used oil via UOA to check the health of the engine and if everything is normal during the first 5 years, just drop the pan to clean out after warranty expires. If UOA indicates higher than normal wear, you can decide what to do then.

And some additional info, pretty sure he is a member on here.

And some additional info that i came across, though cannot be verified as fact or BS.

[Tcoat]

Originally Posted by Petah78

Just keep monitoring your used oil via UOA to check the health of the engine and if everything is normal during the first 5 years, just drop the pan to clean out after warranty expires. If UOA indicates higher than normal wear, you can decide what to do then.

And some additional info, pretty sure he is a member on here.

And some additional info that i came across, though cannot be verified as fact or BS.

The oil samples are great if it is a gradual thing but pretty sure that all the ones reported were sudden and catastrophic. Oil stopped flowing to that one bearing and within minutes it was toast. No oil test in the world would forecast that scenario.

[Petah78]

Originally Posted by Tcoat

The oil samples are great if it is a gradual thing but pretty sure that all the ones reported were sudden and catastrophic. Oil stopped flowing to that one bearing and within minutes it was toast. No oil test in the world would forecast that scenario.

How did you conclude on that?

[Tcoat]

Originally Posted by Petah78

How did you conclude on that?

The info that we have got right now says:
All happened with prior zero indication of a problem at a very low mileage.
All the reports that gave details have said a single bearing went out.
All oil samples from engines with no problems have come up good.


Unless we get differing data the trend is glaring.

[Petah78]

Originally Posted by Tcoat

The info that we have got right now says:
All happened with prior zero indication of a problem at a very low mileage.
All the reports that gave details have said a single bearing went out.
All oil samples from engines with no problems have come up good.


Unless we get differing data the trend is glaring.

I concur with all your stated facts. But what are possible warning signs for a spun rod bearing? All the reports of failure that i have seen are for a single rod BUT i have also not seen other bearings from the same engine (maybe i missed this?). My theory is that this can be a sudden or a gradual death, and in the event of a gradual problem, UOA will pick it up.

[Tcoat]

Originally Posted by Petah78

I concur with all your stated facts. But what are possible warning signs for a spun rod bearing? All the reports of failure that i have seen are for a single rod BUT i have also not seen other bearings from the same engine (maybe i missed this?). My theory is that this can be a sudden or a gradual death, and in the event of a gradual problem, UOA will pick it up.

Agree there is a lack of info on other bearings since most find the one and "OK there is the problem we are done here" but there have been enough saying just the one that I am comfortable in making the statement.
If there was even one oil analysis that said "we have concerns" I may also change my outlook but there just isn't.

Failure mode and risk analysis of industrial processes are what I have done for 30 years and I will say that with what we have I am about 75% confident that these failures are sudden. I would be happy to change that level (up or down) with a nice big data set but I don't think we are going to get much more info than we already have. Really the only new data I expect is if the mileages go up and there are still multiple failures but at this point they seem to have stopped. Or at least no longer get reported!