Martin-Hadland

iTrader: (2)

oops perhaps i should have read the whole thread... i thought it was the oil breather drain, not the turbo!! In which case i don't see a problem with returning above the oil level as yb cos.
sorry for the misunderstanding.

Mark V8

iTrader: (2)

Space was REAL TIGHT on my bike setup and I had hardly any room for oil return. It is at the bottom of the sump and oil level is just below the bearing core on the turbo but I've had no issues at all with oil consumption/smoking etc.

Plumb it in where ever it will fit and forget about it

Mark

heeman10

Interesting one there Mark, and did you take that labelled up picture specially for us?

Martin - Slapped wrists

Fiecos Dan

i've also believed turbo oil returns above oil level, reason is cos oil will drain alot faster.

But if a oil return of Breather, then below, so not affected by crank case pressure, and will drain oil.

rich_frst

iTrader: (3)

anyone else.....

thanks for the picture mark, if it works well then i'm sure i wont have a problem, thats what i was told is a good location it works well, faultlessly...

and has done time and time again...

plenty of people on here use paul hills @ EA and they dont have problems, so why should i ?!? we'll see... i'm speaking to him tomoro and i'll see what he makes of all this...

foreigneRS

has the simple fact that a liquid finds it's own level escaped you all?

rich_frst

iTrader: (3)

no mate, thought that

but quickly forgot when i was told i'd made a big mistake in having it fitted there

heeman10

Not at all. How are you relating that to this problem?

foreigneRS

i'm just saying that it doesn't matter if the turbo oil return goes above or below the oil level, as the oil level will be the same whatever.

it's not like if you have the return under the level that it will then build up in the pipe as it will just level out.

i don't think i'm explaining it very well

Fiecos Dan

No,

but different fluids take longer than some to level them selves.

and thats not taking into account of a car moving, and going round corners @ 100+ mph
(G forces), and gravity forces.

Plus the other variable of crank case pressures.

heeman10

The oil will level out yes, but this discussion concerns the position of the oil return, and whether it should sit above or below that natural level. So what you say is true, but doesn't affect the original question: Should the turbo oil return go above or below the oil level.

It sounds like I'm being arsey, but I'm just clarifying just what the question is here

foreigneRS

i understand that the point of the question is to find out if it matters if the return is above or below oil level - but what's the difference?

heeman10

If you read my replies you'll see Read the stuff about pressure differentials and flow rates right at the beginning

foreigneRS

i have read it. and the point about pressures doesn't make sense to me - surely the oil will transmit the crankcase pressure to the return pipe anyway?

heeman10

The oil will transmit crankcase pressure, yes, but the crankcase won't transmit the oil pressure. That's the key to this discussion/query

foreigneRS

what oil pressure? don't get it

heeman10

The pressure the oil in the sump exerts on the walls of the sump. Pressure in a fluid = density x depth of fluid x gravity. So the deeper the fluid (i.e. the lower down in the sump the oil return fitting is), the greater the pressure being exerted on it is. Say the density of oil is something like 800kg/cubic metre (total guess), the oil in the sump is 100mm deep, and gravity's 9.81 m/s/s, that gives a pressure of 785 Pascals, or 0.008 bar, or around 0.1psi. The oil pressure to the turbo's going to be around 60psi or so, so that 0.1psi doesn't necessarily make a big difference in THAT respect. Bear in mind the crankcase pressure can be added to this pressure.

However, the rate at which the oil drains away to the sump after the turbo does make a difference. The oil return hose is a larger diameter than the oil feed hose to the turbo, and so the pressure isn't as high. The pressure and viscosity of the oil in the sump create a backpressure for the oil trying to drain into the sump under gravity, and so rather than freely draining away from the turbo, I believe it will be pushing stagnant oil down the return hose and into the sump, which I suppose may increase oil pressure in the bearing. Whether that's a good thing or a bad thing I don't know, but those are the principles I'm working to.

evergreen72

I not as high educated like many of you i have my own thinking.

it should not matter where oil return is above or below oil level, the oil return pressure will force oil out maybe slower if under oil level but this is no matter to turbo there will be oil being pushed into turbo so no starvation even under g force.

If return above oil level it can splash ontop of baffle making drag on crank so not too good for high rpm?

crank case pressure be same rate both way? positive crank case valve controls breathering no? could this concern overcomed by using higher pressure oil feed or oil pump?

foreigneRS

none of that matters, as the oil return hose is never full. it's only a fraction of the diameter of the drain tube that is used so it has no effect on the bearing

heeman10

evergreen - I don't think starvation's a question here, it's more the issue of the post-turbo oil draining back to the sump successfully under gravity, rather than being "pushed" back into the sump, as you've suggested would happen. I think by doing that, the oil pressure would be raised a certain amount, though I'm not sure what bearing (excuse the pun!) that would have on the rest of the engine, e.g. oil pump, drag associated with elevated oil pressure, and bearing operation.

foreigneRS - I think what could happen is that even though the drain hose is much bigger than the feed hose, the backpressure would/could cause the return hose to stay full of oil. It depends on crankcase pressure, but all these "ifs" and "buts" are what make me against having an turbo oil return down there at the bottom of the sump. I'd want the peace of mind an elevated return would give.

scruffythefirst

There is no way crank case pressure could be high enough to support the volume of oil required to fill the return pipe, without having other more serious problems to worry about. Any oil returning through the pickup pipe will fall pretty quickly through whatever gas is contained in the pipe at whatever pressure.

Anonymous

Even if the hose isnt full you could still say pressure from the air sealed in it having nowhere to go, if the pipe is above the oil level the air doesnt have to bubble through it first to evacuate the pipe.

scruffythefirst

No air will be entering the pipe, just what is there from when it was assembled, the pressure inside it will be equal to whatever the pressure is in the crankcase, so it makes no difference whatso ever.

heeman10

Matt - That's right, provided there's an equal pressure in the sump and the return hose. Your pictures are good enough to explain part of the situation, glad someone could be bothered!

dave cos4x4

iTrader: (5)

edited for now.

heeman10

Dave - Does that affect the height of the return though? Not quite surewhat it is you're pointing out to us there. Was it moved upwards so the oil's returning about the sump oil level?

heeman10

That's just the thing, the pressure of the oil in the return hose is very low, as it's such a large bore compared to the turbo feed hose.

dave cos4x4

iTrader: (5)

will sort a pic out to show you.

dave cos4x4

iTrader: (5)

edited as i think it was the dip stick pipe.

will go and check again.

evergreen72

why not same diameter oil return hose? then this oil return hose will be in pressure always full of oil this would be good no?

i see having such big hose will risk air lock and drainage problem like house gutter in heavy rain the down pipe gurgles this would same happen with pulse in turbo making damage?

heeman10

No, we're not agreeing that. The turbo oil return is gravity fed, so we don't want pressure at the bottom acting against the drain.

Dave - Back in your box!! Turbo oil return via the dipstick, it's the new black!

evergreen - no, we don't want a pressurised oil return, as the backpressures could hinder oil circulation through the turbo bearings.

scruffythefirst

Correct, but the pressure in the return will be the same as the crankcase pressure, whichever way it's returned to the sump.

heeman10

No it isn't, it also has the pressure head created by the depth of the oil, as it says in one of my replies further up. Viscosity will also add a reactive force to the oil entering the sump from the turbo.

evergreen72

is bad for oil return hose to be pressured so oil should drain out this hose use gravity not forced out; this good for the turbo correct? oil forced out bad for turbo? why?

if oil return is above oil level sump then drain through oil return hose is free it is best this way. if oil return hose smaller and oil forced out then it does not matter if below oil level the oil is pushed out into sump under baffle plate so it ok like this.

dojj

iTrader: (3)

returnging the oil above the oil level seems to have been exlained proplery, this way the oil can be let back into the sump under it's own wieght (plus the force at which is it being pumped into the turbo)

oil returns below the oil level have only been done on 2 cars, the 24V granada engine and some sort of audi, everything else seems to have a return above the oil level

at the same time you can't use the dip stick hole to return the oil either

scruffythefirst

Canceled out by the head of the oil in the return pipe. It works exactly like a barometer. U shaped tube open to the air at one end, liquid in the bottom and sealed at the other, the level of the water changes to keep the pressure constant in the sealed end of the tube as atmospheric presure changes.

So, the pressure in the crankcase is equal to the pressure in the return pipe, accounting for negligible oil viscosity and changes in crankcase presure, the level of the oil in the return pipe will be almost exactly the same as the sump level, and the pressure in the pipe will be the same. So it makes no difference if you return above or below the oil level for pressure or oil level reasons.

I can do some paintshop pictures if you want.