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

[Code Monkey]

Going with the Tomei baffle.

[timurrrr]

Originally Posted by Grif

A close up and personal inspection of the oil pickup screen/basket.
Really gives you perspective of the surface area at play.

https://twitter.com/yonsama800/statu...69665373138945

That's an awesome find!

As some people don't have time to click every link in this 50+ page thread,
but those photos are very important to understand what's going on,
I'll take the liberty to re-post them here:

[ZDan]

Originally Posted by Petah78

Thank you for posting this info. I have long suspected that the top doesn't represent a large percentage of the total surface area of the pick up but this post confirmed it. The 4 sides looked to have a much larger surface area and by estimation, i say the top is about 1/7 (14%). I wouldn't think flow is the problem even if the entire top side is blocked. Cavitation is a real concern though. I am not an engineer but i think cavitation will only become an issue with:

- Higher oil temps
- Higher pressure differentiation pre/post pump (how bad the blockage is)

Any engineer can confirm?

I'm an aerospace engineer specializing in structural design/analysis, but I have taken courses on fluid mechanics...

I would say that while the upper screen portion may only be ~15% of the screened area, it is by far the most important 15%! The fluid can easily pass through the open areas on the screen as it's traveling perpendicular to it. On the sides, the flow is roughly trying to flow more parallel with the fluid flow. It's going to present much more of a blockage, and in addition will locally force the flow more perpendicular to the direction it needs to be going in.

Something of a WAG but I'd say blocking off the top portion of the screen only and leaving the sides open could represent something like a 50% blockage... Might be OK for piddling around at low rpm but I would *not* want my car to be taken above 5k rpm with any frequency with that kind of blockage.

[Tcoat]

Originally Posted by timurrrr

That's an awesome find!

As some people don't have time to click every link in this 50+ page thread,
but those photos are very important to understand what's going on,
I'll take the liberty to re-post them here:

It is an interesting perspective and the surface area would be wonderful if that was out in the open like that. Yes the sides are substantial but once enclosed in the tube the flow drawn through them would be greatly reduced since the gap between them and the tube sides is not very large. The bulk of the draw is still going to be across the end not spread evenly across the whole surface area.
It does support the theory that there is more than just the plugged pickup at work though.

[timurrrr]

Originally Posted by ZDan

I'm an aerospace engineer specializing in structural design/analysis, but I have taken courses on fluid mechanics...

I would say that while the upper screen portion may only be ~15% of the screened area

How about geometry though? :P

My most conservative eyeball estimate is that each of the larger sides has 3x the surface area of the top; and the smaller sides are at least as large as the top.
That gives the top at most 1/9 of the total surface area (~11%), and more like <10%.

[ZDan]

Originally Posted by timurrrr

How about geometry though? :P

My most conservative eyeball estimate is that each of the larger sides has 3x the surface area of the top; and the smaller sides are at least as large as the top.
That gives the top at most 1/9 of the total surface area (~11%), and more like <10%.

OK, if it's 10% of the screened area, it is *by far* the most important 10% of that area for reasons already stated.

I certainly wouldn't look at blockage of that area and conclude that it's no big deal...

[ZDan]

Also, even though the outer tube bulges out a bit, if the central area is blocked, the flow around the sides is going to have to make a hard turn to fill in behind the blockage, creating opposing vortices that will further act to reduce flow. Probably not as bad as trying to run fluid the "wrong" way through a Tesla valve but kinda in that direction...

[Tcoat]

Originally Posted by ZDan

OK, if it's 10% of the screened area, it is *by far* the most important 10% of that area for reasons already stated.

I certainly wouldn't look at blockage of that area and conclude that it's no big deal...

Damn we were writing at the same time!

[ZDan]

Originally Posted by Tcoat

It is an interesting perspective and the surface area would be wonderful if that was out in the open like that. Yes the sides are substantial but once enclosed in the tube the flow drawn through them would be greatly reduced since the gap between them and the tube sides is not very large. The bulk of the draw is still going to be across the end not spread evenly across the whole surface area.

Agree with the above ^^^

Also consider the cross-section of the tube where the top of the screened box is, and the area of the top of the screen relative to *that* cross-sectional area and not relative to the total screen area. And *also* consider that with all screens clear the flow velocity in the *middle* of that area (i.e. the horizontal upper screen area) is greater vs the perimeter. Blocking out the upper horizontal screen (middle of that area) is gonna be very bad for total flow rate...

[Tcoat]

Originally Posted by ZDan

Agree with the above ^^^

Also consider the cross-section of the tube where the top of the screened box is, and the area of the top of the screen relative to *that* cross-sectional area and not relative to the total screen area. And *also* consider that with all screens clear the flow velocity in the *middle* of that area (i.e. the horizontal upper screen area) is greater vs the perimeter. Blocking out the upper horizontal screen (middle of that area) is gonna be very bad for total flow rate...

Ya that is what I was writing while you were doing pretty much the same.
Cramming a square filter into an oval tube that tapers in immediately after the box ends isn't giving a pile of clear flow around those sides either.

[Spektyr]

Originally Posted by ZDan

I would say that while the upper screen portion may only be ~15% of the screened area, it is by far the most important 15%! The fluid can easily pass through the open areas on the screen as it's traveling perpendicular to it.

Just wanted to point out that the pictures of trapped RTV in the screen proves this out, for any who don't have the background in physics to just see that instinctively.

Foreign objects in a fluid flow will get caught in a screen at the point of higher flow first, because there is more/stronger flow in those locations. If a piece of RTV got sucked onto the side before the end was completely blocked the flow through the open part of the end would pull that RTV along until it filled that gap.

It's a fairly simple way to test where your flow is strongest.

[DocWalt]

I'm glad Dan was able to succinctly explain what I've been trying to explain to the morons on facebook that are always like "omg that's so little blockage" because they don't understand fluid dynamics in the least.

[ROFL it's Waffle]

Noob questions: I see the diameter of the pickup tube. How much oil is being sucked up at once? Is it a slow suction or fast? (not sure how to quantify this, maybe in cups per second or quarts per minute?)

If RTV is to be sucked up in there, is it instant? (slower/weaker flow, happens over time; faster/stronger flow, happens "instantly" or much quicker)

Could the tube be under-sized? (I know, regardless of size, a blockage leads to starvation)

[Spektyr]

Originally Posted by ROFL it's Waffle

Noob questions: I see the diameter of the pickup tube. How much oil is being sucked up at once? Is it a slow suction or fast? (not sure how to quantify this, maybe in cups per second or quarts per minute?)

If RTV is to be sucked up in there, is it instant? (slower/weaker flow, happens over time; faster/stronger flow, happens "instantly" or much quicker)

Could the tube be under-sized? (I know, regardless of size, a blockage leads to starvation)

I could be wrong, but my understanding of fluid dynamics would say that there's a fairly small range of variation in diameter that would work. The inlet/outlet diameter of the oil pump itself is a big factor. At some point you have to funnel the pickup tube up/down to that size.

As your pickup tube diameter increases beyond the size of the oil pump inlet you're going to see less flow around the outside because the pump cannot lift the entire volume of oil in the tube uniformly. The height of the column of oil is set, so the wider you make the pickup the heavier that much oil becomes and the pump has only so much lifting power. The result will be a column of oil within the total volume that actually moves upward, concentrating any particulates or chunks suspended in the oil to that part of the screen.

As the center of the screen gets blocked, the column will "hunt" around for an unblocked path, kind of like a tornado looking for a trailer park.

Again, I'm not certain, but my guess would be that the smoothest, most efficient (laminar) flow would be achieved when the tip of the pickup tube is at or very close to the same surface area as the inlet of the oil pump, so I doubt that it's undersized.