I wanted to know if any of you guys have un hooked your oil return line from the turbo and started your car did oil come back up the oil return line? if so what would cause that?
Thank YouCorbitt
KA-t return line question.
Re: KA-t return line question. (bankrup3000gt)
Positive crankcase pressure... wherever you tapped in or welded on the bung or pipe to the oil pan was too low (below the level of the oil) and the crankcase pressure is pushing oil back up the pipe. Obviously, the oil coming into the turbo from the feed line has more pressure, but it will probably still let oil linger int eh turbo lnger than it should. If it were me, I would fix it. Is your PCV valve working properly? Replacing it would be a lot easier than moving the bung or pipe on the oil pan. Good luck.
I'm with Mikerbike in that there's definitely excessive crankcase pressure going on there. I'd say most likely either the PCV valve is bad or you either re-routed the valve cover PCV system port to a catch can OR just put a little mini-filter on it. Either way, it's guaranteed to make too much crankcase pressure.
The PCV system is a positive pressure system and that valve cover port needs to be fed from the air intake stream (pre-turbo). The venturi effect comes into play here, and there's about 0.5psia or less in that line, forcing PCV scavenging. Without this pressure, air gets trapped under the pistons and causes blowby and, in this case, back-up into the turbo drain line.
Moving the oil bung above the oil level would prevent the oil from blowing back up the line, but it still doesn't fix the pressure problem in the crankcase. In a good engine with appropriate crankcase pressures, the oil return bung could be below the oil level in the pan with no ill effects.
We recently had a very heated discussion about drain line bung location and the thread got locked because someone didn't believe in the science that proves through fluid dynamics that column stacking is the determining factor in whether or not the line would back up. Basically, if the oil drain supply is vertically higher than the container into which it is discharged, the placing of the discharge doesn't matter. It can be above or below the fluid level in the discharge container.
Furthermore, it's also perfectly fine to have a small "dip," if you will, in the oil drain line. Mine has been that way for 20k+ miles and I have no oil backing up the return line. Imagine the "P" trap in a kitchen sink drain.
So, to the poster of this question: Check your PCV routing system. If all is in order and you still have considerable blow-by, most likely your rings are excessively worn and a rebuild or engine replacement is in order. If the PCV system checks out (connections are appropriate and PCV valve is operating), do a compression test and/or a cylinder leakdown test and let us know what you find.
The PCV system is a positive pressure system and that valve cover port needs to be fed from the air intake stream (pre-turbo). The venturi effect comes into play here, and there's about 0.5psia or less in that line, forcing PCV scavenging. Without this pressure, air gets trapped under the pistons and causes blowby and, in this case, back-up into the turbo drain line.
Moving the oil bung above the oil level would prevent the oil from blowing back up the line, but it still doesn't fix the pressure problem in the crankcase. In a good engine with appropriate crankcase pressures, the oil return bung could be below the oil level in the pan with no ill effects.
We recently had a very heated discussion about drain line bung location and the thread got locked because someone didn't believe in the science that proves through fluid dynamics that column stacking is the determining factor in whether or not the line would back up. Basically, if the oil drain supply is vertically higher than the container into which it is discharged, the placing of the discharge doesn't matter. It can be above or below the fluid level in the discharge container.
Furthermore, it's also perfectly fine to have a small "dip," if you will, in the oil drain line. Mine has been that way for 20k+ miles and I have no oil backing up the return line. Imagine the "P" trap in a kitchen sink drain.
So, to the poster of this question: Check your PCV routing system. If all is in order and you still have considerable blow-by, most likely your rings are excessively worn and a rebuild or engine replacement is in order. If the PCV system checks out (connections are appropriate and PCV valve is operating), do a compression test and/or a cylinder leakdown test and let us know what you find.
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bankrup3000gt
- Posts: 71
- Joined: Thu Mar 18, 2004 3:41 pm
Re: KA-t return line question. (bankrup3000gt)
Here is a little drawing of my setup. All of this started with oil coming out the valve cover breather after about 20 miles on the turbo set up. I have a -3an feed line and -8an return line with the return bung welded about 3inches back from the front of the pan and about 1inch down from the top. I have the return line wraped under the ac compressor then up to the turbo.
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bankrup3000gt
- Posts: 71
- Joined: Thu Mar 18, 2004 3:41 pm
Re: KA-t return line question. (bankrup3000gt)
I also forgot to add that if you un hook the line at the turbo intake you can feel that air is coming out and you can hear it also.
Re: KA-t return line question. (bankrup3000gt)
Time for a leakdown test (if the PCV valve is known to be good). How many miles are on the engine? Sounds like it's time for a set of rings.