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Old 03-16-2010, 04:36 PM   #1
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Default oil return line under oil level?

Seems I forgot something when I drilled my oil pan ... the return is under the oil level. Should I redo it, or will it be fine?

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Old 03-16-2010, 04:40 PM   #2
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I honestly don't think you'll have an issue. The oil will back up into the drain line, and it'll be a bit more prone to leak, but since the actual drain outlet is still a few inches up I'd like to think it would be just fine.
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Old 03-16-2010, 04:41 PM   #3
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Me personally, I'd redo that.

The oil in the line will always be backed up atleast as high as the level in the pan. Add to that the viscosity and the fact you're now pushing oil into a filled reservoir instead of air, and you've got a recipe for pushing oil past the seals in your turbo.
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Old 03-16-2010, 04:46 PM   #4
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Quote:
Originally Posted by gospeed81 View Post
and the fact you're now pushing oil into a filled reservoir instead of air, and you've got a recipe for pushing oil past the seals in your turbo.
I never thought of this. It's supposed to be a gravity drain, but that assumes you are pumping it into a large area where pressure can't really build up much, not a tiny little area. Scratch what I said, I would move it. Stick an oil temp sensor in the existing hole.

FYI, the oil level is here:
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Old 03-16-2010, 05:14 PM   #5
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Take a straw, and place it into a half-filled glass of water. There is now water "backed up" several inches into the bottom of the straw.

Pour some water into the top of the straw.

Does the water back up to the top of the straw? No, it displaces an equal amount of water out the bottom of the straw, the level of water in the glass rises very slightly, and the level of the water sitting in the straw remains the same as the level of water in the glass as a whole. If you remove water from the glass at the same rate that you are pouring water into the top of the straw (as the oil pump does from the pan) then the water level in the glass and in the straw will remain constant.

Looking at Sav's image, the level of oil in the drain hose will be equal to the level of oil in the pan as indicated by the black line. The rest of the hose will be filled with air. As oil drains out of the turbo, it will run down to the level of standing oil in the hose, an equal amount of oil will be displaced out of the bottom of the hose, and nothing will "back up" anywhere.

Bear in mind that the actual amount of oil going into the turbo, and thus the amount of oil coming out of it, is fairly trivial. If you could pump a torrent of oil into the top of that hose fast enough, then yes, you'd probably get some back-pressure. But we're talking about oil basically drizzling out of the bottom of the turbo, not gushing out of it.


Now, will that return fitting clear the engine mount?
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Old 03-16-2010, 07:24 PM   #6
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Joe, you have 465 cc injectors? No wonder I'm always lean. :-)

Frank:
A friend was doing a "get this done in a weekend" turbo project. I lathed up a banjo bolt, and returned the oil IN THE DRAIN PLUG. Seems to work just fine, and you can't get lower.

Viscosity is an issue, but I don't think you have to worry. Where does the pressure come from? The oil pump.

Side note: This friend burns a lot of oil, but I think it's that he put the motor together with giant gashes in the cyl walls. :-)
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Old 03-16-2010, 09:01 PM   #7
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Also something to think about is that when the engine is running the oil leval is going to be going down. So there may be less of a back up. I you need to replace the pan let me know I have one from my 2000. It is new and never used.

Have a gerat day,
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Old 03-16-2010, 09:17 PM   #8
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This is in violation of the 1st and 2nd rule of oil returns

Quote:
Originally Posted by Rules for Turbo Oil Returns
1) Return must drain above pan oil level.
2) Return must drain above pan oil level.
3) No part of line should dip below level of drain.
4) Return line should not make any harsh bends.
5) No heater hose.

Last edited by Full_Tilt_Boogie; 03-16-2010 at 09:17 PM. Reason: BB code fail
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Old 03-17-2010, 01:09 AM   #9
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ive always done the return to the front of the sump
that hole must be close to the baffels
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Old 03-17-2010, 02:49 AM   #10
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Quote:
Originally Posted by Full_Tilt_Boogie View Post
This is in violation of the 1st and 2nd rule of oil returns
Never mind the oil level, how are you going to fit the motor mount on with the oil drain line there? I'm assuming it's going in a Miata?

Mine, for comparison:



--Ian
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Old 03-17-2010, 09:54 AM   #11
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I always thought there was a fairly amount coming out possibly causing it to back up in the drain. But if it doesn't gush out like Joe mentions, than I tend to think there's not a problem. Also, I tend to think that maybe the oil pickup tube sucking up oil might cause a bit of underpressure resulting in better drainage of the hose (pure speculation of my part).

I'll leave it as it is for now. Thx for the comments guys.

sprsta, the fitting is well below the baffle. I can feel the baffle with my finger and it's at least half an inch up. Even if the hole is higher up, there is a fair amount of space between the oil pan and the baffle that it wouldn't matter.

Jared. I was thinking that as well, but was making myself unneccesarily scared I think. Thx for the offer on the oil pan, but I'm keeping this one, even with an additional hole. It's not very visible in the picture, but if you look closely you can see that I welded on a plate to the side so I had more material to tap into. I'm paranoid when it comes to leaks. The shiny part is the welded on bit.

Ian, the engine is not going in a Miata. As a matter of fact, the engine mount is already fitted in that picture, directly under the waterpump inlet.

Edit: at least my return doesn't look like this one


Last edited by WestfieldMX5; 03-17-2010 at 10:19 AM.
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Old 03-17-2010, 12:19 PM   #12
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^ omfg
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Old 03-17-2010, 12:31 PM   #13
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Quote:
Originally Posted by Joe Perez View Post
Pour some water into the top of the straw.
take same straw and attach a funnel to it...

continuously pour water into funnel.

Does it fill the glass fast enough without the fluid level in the funnel to collect and rise?
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Old 03-17-2010, 02:33 PM   #14
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Mr. Braineack,
With all due respect... WRONG! HA!

It's a reasonably valid point, but look at the line feeding the turbo. It is very small. Imagine you took the turbo out entirely, just hooked the small feed line to the large return line. Could you fill it? Maybe with 150 weight oil at 40*f. The turbo is a huge restriction, as is any "oil restricters" which people tend to put in.

I guess someone could do an experiment.


If the oil returns slow enough to back up, it'll overflow into the catch can. And if not, the can will be empty.

Or, perhaps the easy way - take your funnel and straw idea, and put the straw just under or just above the level of the water. :-)


The real issue in all this, is what's the PRESSURE at the oil seal? if there's an open drain to the oil pan, the pressure is LOW. Probably much more of an issue is crank case venting - regardless of being above or below the oil level... If there's 25 psi of pressure in the crankcase, that pressure will be ADDED to the oil pressure in the drain and in the turbo, then perhaps you could blow your seals. heh. Your mom blows seals.
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Old 03-17-2010, 03:14 PM   #15
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The pressure is low to nil, but volume heavy. I was really posing a question for reals anyways.

Also that catch can idea would be awesome if you added a drain line into the top of the oil pan...



Starter RPM only:



with .060" restrictor on -4AN line:



without:
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Old 03-17-2010, 03:33 PM   #16
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Quote:
Originally Posted by Braineack View Post
take same straw and attach a funnel to it...

continuously pour water into funnel.
Make the opening in the bottom of the funnel, and the size of the straw, appx. 1/2" in diameter.

Pour the water into the funnel through a restrictive orifice with an effective cross-section of about 1/32". You can even pressurize the container of water if you wish.

The water will not back up into the funnel.
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Old 03-17-2010, 03:38 PM   #17
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My oil return is just a bit above the oil level.
Once I accidentally overfilled my oil by 2qts.
Finally realized it when trying to figure out why my turbo was spraying vast amounts of oil out the compressor side.
That was WITH the little rivet restrictor.
Dumped out the extra oil and everything was fine again.
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Old 03-17-2010, 05:07 PM   #18
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Hmm. Difference between theory and application, I guess.
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Old 03-17-2010, 05:09 PM   #19
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2 quarts of extra oil will cause all SORTS of problems, blown seals everywhere. This is not remotely uncommon.

A non-destructive test for this is the catch can I suggested, a windowed oil line like Brain showed, or something similar. Then do the oil pan banjo bolt thing I described. You can't get any lower than feeding your oil up from the bottom of the pan.


Certainly the warmed up video you showed, the last, looked like no trouble at all.
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Old 03-17-2010, 05:29 PM   #20
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2 qts was a guess, I had just put the motor in and forgot that I had dumped some oil in it to check/prime the oil system. Dipstick indicated the oil level was almost exactly inbetween full and the top of the pan, but it was hard to read of course.

Out of curiosity, how does it 'blow seals everywhere'? I've hear that before but never witnessed it. Seems like all that would happen is that the crank would maybe froth up the oil a bit if you drove it that way. I know foamy oil sucks for bearings, but why would the seals care?
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