Basic Fluid Dynamic Question (Oil Return on Turbocharged Car)

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Discussion Overview

The discussion revolves around the oil return system in a turbocharged 1979 Volvo 240, specifically addressing concerns about potential drainage issues due to the angle of the engine and the design of the oil return line from the turbocharger to the oil pan. The scope includes fluid dynamics and practical implications of automotive engineering.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant describes their setup, noting that the oil return line has a slight upward section due to the engine's angle, and questions whether this will cause significant drainage issues.
  • Another participant compares the situation to a garden hose, suggesting that while there may be some rise in the oil level in the drain hose, it will not lead to major drainage problems.
  • A different viewpoint mentions that increased crankcase pressure during boost could slightly raise the oil level in the drain line, but still believes that fluid will continue to flow effectively.
  • One participant shares their experience with turbo installations, indicating that a pint of oil flows through the turbo per minute, implying that flow rates are manageable despite the design concerns.

Areas of Agreement / Disagreement

Participants express differing opinions on the severity of potential drainage issues caused by the upward section of the oil return line. While some believe it will not significantly affect flow, others suggest that crankcase pressure could complicate the situation. No consensus is reached on the overall impact of the design.

Contextual Notes

There are assumptions regarding the behavior of oil flow under varying pressure conditions and the effects of crankcase pressure that remain unresolved. The discussion does not clarify the exact implications of the engine's angle on oil return efficiency.

propav8r
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Ok-I'm actually looking to settle an argument on another forum. I have turbocharged my 1979 Volvo 240, and converted to a later style motor. Instead of drilling and tapping the boss in the block for my oil return to the oil pan, I welded a 1/2" NPT bung into my oil pan. The approximate inner diameter of that bunt is 5/8".

The oil drain outlet from the turbocharger is also approximately 5/8" inner diameter, giving more or less the same hose diameter all the way back to the oil pan from the turbo drain.

Here's the argument though. The engine is canted approximately 15° over to the exhaust side, meaning that the oil return has a slight upward section before it dumps into the oil pan.

My line of thinking is that the oil level in the drain hose will back up some, but only to the level of the line outlet. Others seem to think that it will cause major drain issues, which I just don't see.

I should probably mention that turbo oil drains don't see only pressure, only flow. The turbo itself is fed from a -4AN line with pressure varying from 4 bar to 1.5 bar, but once the oil has gone through the turbo, it loses it's pressure.

Can anyone more well versed in fluid flow than myself help me answer the question? I've included a pictoral for further explanation.

IMG_3677.jpg
 
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Heh-206 views and no answers...
 
ben-stein_1.jpg
 
So what would a garden hose do in the same situation? Allow flow and when the flow was removed the only fluid left would be even lower than your blue marker. When your engine is making boost, the crankcase will get more blow by and increasing the crankcase pressure a little bit. This might cause the drain level to rise up a bit (no more than 1/2 an inch) but the fluid will still flow.

It is not ideal but with your turbo mounted higher, you won't have a drainage issue. FYI about a pint of oil will flow through your turbo per minute. I have added turbos to three separate vehicles.
 
That was my line of thinking.

As for pressure in the crankcase, there shouldn't ever be too much-my PCV isn't recirculated. I'm just using a road draft tube instead. Not too friendly for the baby seals, but we've got too many of those already. :smile:
 

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