Need clarification: oil return

[TravisD]

OK, so if I have my bung welded into the oil pan between the A/C bracket and the engine mount bracket, about 3/4" down from the flange, I won't need to run low on oil, correct? How high is the oil level in the pan? I figure I'll have it put in angled up so it's at least horizontal coming in.Thanks

[AZhitman]

That is correct.

The most important part is to make sure the oil is on a downgrade the whole path, ideally perpendicular to the ground.

The closer to the flange, the better. I even sacrificed one oil pan bolt to get mine as far up as possible.

[TravisD]

Thanks for the reply. I've got an engine almost done, no turbo for a few months, but I'm going to have the bung installed before it gets swapped in next week (hopefully). I'm assuming you are absolutely positive the absence of that bolt won't be a concern?

[KATwo40]

Every time I see one of these "Oil Return location" threads, I'm reminded of a post from Edub1 a while back, that was eventually locked.

I disagree with the concept that the oil return MUST be above the oil level in the pan. The oil will always seek equilibrium. My oil drain line goes UNDER the A/C compressor and back up near the top of the pan, but not at the topmost location, since I wouldn't be able to get the hose on the fitting up there. I don't have issues with oil backing up into the turbo.

If you've ever looked under your kitchen sink, you'll recall seeing a "P-trap" where the pipe dips below the drain line in the wall. Same concept with the oil return line.

In the end, it's all about column stacking. Furthermore, once the engine is running, even at idle, I doubt there's more than 2-2.5qts of oil in the pan, which would bring the level down around half the sump area. So, even if the bung was welded halfway down the pan, the oil wouldn't be "backing up into the line," as so commonly believed to happen.

Not tryin' to stir any crap here, just participating in the conversation.

EDIT: It's also important to take into account the size and pressure differences between the two oil lines (supply/return). The supply line is going to be pumping oil through a hole around 1/16" (+/- 1/32", depending on restrictor and/or fitting diameter). While the pressure in the line might be 50-60psi, the oil pressure in the turbo will be probably no more than around 35-40psi (because of the restrictor or -AN fitting orifice size). The return line is MANY times larger than the supply line, and the drain is gravity flow, not pressurized flow. It's highly unlikely that the return line will get stopped up because the oil runs into another pool of oil in the pan.

[Florida240sx]

The only issue of oil being backed up is on mountain drives or drifiting event etc. But even then it's never really a problem because not enough blockage to do any harm for so little time. Unless you are on a banked speedway...

[KATwo40]

The only issue of oil being backed up is on mountain drives or drifiting event etc. But even then it's never really a problem because not enough blockage to do any harm for so little time. Unless you are on a banked speedway...

I live in East TN. It's pretty mountainous here. I also frequent the "Tail of the Dragon," which is a 2-lane road between TN and NC that is 11 miles long, containing 318 curves. I also have run on the local banked oval (411 Motor Speedway). No backing up in the oil return in either environment.

However, the hard G-forces resulting from these environments do create a high probability of oil slinging up out of the sump area against the sides of pan, causing some oil starving issues. But that's not really related to the turbo drain line issue.

[TravisD]

Not tryin' to stir any crap here, just participating in the conversation.

Well, thanks for participating in the conversation. Also, thanks for answering my question about how much oil is left in the pan. What you say makes sense. I saw posts about people having to run low on oil; I thought the problem may lie in the speed at which the return line drains. Now that I think about it, considering what you've said, even if the return line wasn't draining fast enough, the pressure of the oil from the feed would push that in the return through, right? Wouldn't it just become a pressurized line in that case? It seems like your edit is implying that the pressure from the feed is enough to overcome any backup instead of the feed being overcome and stopping. I wasn't sure how forceful the feed is, but it really sounds like there's no possibility for oil to back up. How long have you been running this setup?

[KATwo40]

I'm not necessarily implying that the feed will pressurize the return. This would be a bad thing, as it would blow the oil out past the piston ring (inside the turbo...not the engine) and cause a smoking issue. MarkEmark just wrote up a post on this because he had some coked up oil block off his return and make a smog machine out of his car.

The point of my edit was to show that the oil drain line is more than capable of freely flowing the oil supplied by the feed line.

Fluid demands self leveling. This is a known fact. If I have a tube that's 2ft tall and it has a "P trap" on the bottom, feeding into the bottom of a bowl with 4qts of fluid, whatever I pour into the tube will not back up into the tube (given adequate tube diameter for the fluid's given viscosity) and overflow because of the pressure created in the bowl, pushing downward on the fluid coming in.

Instead, the fluid will flow through the "P-trap" into the bowl, until the fluid in both the tube AND the bowl reach an equal level.

[TravisD]

gotcha. Thaks for the great replies, you've been very helpful. I'm not so worried about it now, and I'm definitely not going to run minus an oil pan bolt.

[hannibal]

Good thread...KATwo40, your example works only if the pressure of the bowl and the pipe are the same. Not sure if the theory works for the drain line, as the pressure in the line at the turbo could be different than the pressure in the pan. Just throwing that out there to hear your ideas...

[KATwo40]

There's no pressure in the oil pan. You could run the return line into the bottom of a pan holding 9 qts of oil and, so long as the drain line is higher than the oil level in the pan, the oil will push up into the pan, achieving equalibrium.