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As someone whose hot idle oil pressure can be in the low teens, I’m leaning towards Curly’s view. I’m not sure of the scales on the data log I see, but it doesn’t leap out to me as something scary.
Ask me how I know, but on a swap like this, I’m much more inclined to believe there was some failure or “gotcha” in swap parts or assembly that caused the issue. Glad replacements are cheap, sorry you’ve got to go down that road already.
Honestly though, shouldn’t we just blame this on shitty VW engineering?
After few days of street driving and tuning, only one major issue had come up. This thing loooooves to throw belts. And this is a pretty common 07K issue. The front dampener doesn't dampen like... at all, and belts go YEET during quick RPM changes or over ~7200RPM despite tightening them to rubber band levels. There's a few fixes to this, but they all take a little time, so as a temporary stop gap I:
Ordered 8 spare belts
Welded an extra large washer to the front of the alternator pulley to help keep a flopping belt on the pulley.
This, along with lowering the RPM limit to ~7300, kept the belt on... most of the time. I still had the 8 spare belts on hand, so worst case I would go though a belt a session. Again, a very temporary, weekend stopgap measure.
The bumper and fenders came together enough they could be ziptied to the car. I didn't have time to properly fit up my shitty carbon splitter, so I grabbed an old plywood splitter that had been sitting in retirement for a few years, popped some new mounts on it, and threw it on. To help hid the layers of fiberglass and 3D print I hit the entire thing with some black spraypaint.
Thursday night I fired the car up to load it on the trailer and found the alternator had ceased function. Highly inconvenient, as the super light and compact ES1015 isn't something available off the shelf, and the spare I had ordered wasn't showing up for a few days yet. In hindsight, picking something that couldn't be sourced locally was perhaps... not the best idea, despite the appeal of its size and weight. Out of options, I grabbed a K24 alternator that had still stuck around, and made some super ghetto modifications to the pulley and bracket to make it mostly fit. It wasn't pretty but it was on there.
Drove down to RRR for NASA's Friday test and tune sessions. Where the motor rapidly un-alived itself. One paced lap under full double yellows, one lap I just chilled behind a thunder roadster watching indications and waiting for something to fall off the car, then as nothing had exploded I actually started to push it a little and carried some speed into the T1/2 complex(a long sweeping right hander). Oil pressure alarm flashed on the dash at exit, and I heard bad noises pretty soon after that. Two laps was all this one managed. Not exactly how I would have wanted the day to go.
The initial trackside diagnosis was oil starvation- it all lined up pretty neatly. OIL LOW PRESS flashed, bad noises started, and datalog seems to support this as there is a dip to 14PSI right before the knock sensor starts going crazy.
(Top is speed in green, MAP in blue, bottom red is oil pressure, teal is knock, white is RPM over about a minute of time)
Originally Posted by SimBa
Out of curiosity, did you have oil pressure protections set up in the ECU? I always wonder how well those actually work to save an engine in a situation like this.
Yes, but they are mostly for low to zero pressure events. I always had pressure drops under braking, so to avoid false triggering the oil pressure cut was something like "if oil pressure less then 10PSI for more then 5 seconds, shutdown".
Originally Posted by thebeerbaron
As someone whose hot idle oil pressure can be in the low teens, I’m leaning towards Curly’s view. I’m not sure of the scales on the data log I see, but it doesn’t leap out to me as something scary.
So these comments got me thinking, and I looked into the datalog a little bit harder. While the motor does see a drop down to 14psi right before the bearing sheds itself, it was already picking up some noise before that. And I too have seen motors drop down to ~10PSI under low load events and not die. So one drop to 14PSI doesn't seem like it should have been fatal. But this motor was consistently dropping from 70PSI in a straight line to as low as 20PSI once any sort of lateral G was introduced. Not really ideal, and the pan/baffling situation can be greatly improved.
(Circled in red are all the oil pressure drops off of peak, note they don't really correspond with a decrease in RPM(white), its all drop from pan slosh. Also note how knock(teal) stays quiet till the last few corners when it spikes up dramatically. This is a log over 4 min of time.).
I pulled the motor apart to see what had really happened. Bearing damage on all 5 would point to a wholesale oiling issue- it starved, simple as that. But if the damage was localized to only one bearing, then this could have been an isolated event that wasn't caused directly by the slosh.
Dropping the lower pan... yup, that's a lot of bearing material for sure.
Hmm... looks fine here... wait, whats that peaking out of #4?
Ordered left to right, 1-5.
Not even 5 cylinders can escape the course of #4 always being the cylinder to blow.
But #1-3 and #5 bearings looks... not exactly perfect, but not anything close to being spun like #4 was.
Originally Posted by curly
I will say, I’ve seen a number of engines dip to the teens on track and not immediately knock. While improvements can always be made, I’d chock this one up to bad luck from a junk yard engine.
Originally Posted by curly
Yeah, but does the motor have 200,000 miles of 10,000 mile oil changes on it? Was it leaking like crazy and down to 3 of 5 qts or less for most of those 10,000 miles? Was it driven by a 17 y.o. dude trying to impress his gf or a grandma? Too many variables to say for sure that low oil pressure immediately causes knock on these engines, that’s my main point.
I think this is the main takeaway from this. While the oiling situation and my pan design can be GREATLY improved, this motor did not starve itself to death like initially thought. This was probably just luck of the draw from a junkyard, unknown history, unknown mileage motor. I'll be redesigning the oil pan to reduce slosh and pressure drop, and add an accusump to take care of any transitory drops.
Not too beat up about loosing this motor- one of the reasons I selected it to start with is these are cheap and plentiful. While more then two laps would have been nice, I always expected to blow up a few motors in the process, and don't have any intentions of building one for a while yet.
Yikes... Seeing oil pressure drop while RPM increases
My oil pressure protection is mostly just, "is the drain plug in the oil pan" type of protection as well, but maybe you can get a pressure vs RPM table setup to help catch this sooner if it happens again. I'm sure you've already thought about that or implemented that though.
Any chance it was something other than just a lack of baffling, like a pickup tube issue? Seems like those drops are pretty dramatic even with an OEM pan.
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