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Why is my catch can filling up so fast? Looking for troubleshooting ideas


QuaTTro
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Car is a 1990 Audi 2.2L 5cyl (non turbo) running on Standalone ECU with no MAF

 

Yesterday when datalogging and tuning the car, after about 10 laps the catch can was overflowing.  We brought the car back to the shop and did Leakdown, Compression and boroscoped the cylinders.  All of those things looked good and no issue found.

 

The only thing we're thinking now is that the crankcase vent hose that runs to the catch can is routed poorly and it allowing oil to collect in the hose instead of draining mostly back into the engine.  Kinda like a sink "trap" situation.  We've raised the hose up so that it is closer to the factory routing and angles.  Gonna test again tomorrow but I feel like we're just guessing now.

 

I'm looking for ideas on what might cause this and what we might test or look into next.  Thanks in advance!

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Baffle and hose routing could be an issue. I am having a similar issue where crankcase pressure is causing oil leak on BMW “bitch tube”. I’m looking at a larger vent tube and more open catch tank to prevent pressure buildup. You could have it drain back into the engine too

Edited by TimS
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17 minutes ago, Ian said:

Do you run standard oil level?  Some cars are very sensitive to overfilling and the slosh causes a lot of windage which ends up being pushed out the breather during cornering.  Have fought this on subarus and Nissans.

Yeah we did find that we had overfilled some during this last test day, so that would've been part of the problem.  Plus the direction of the track that day has hard, steep uphill off camber corner that would push the oil in the direction of the breather hose.

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4 hours ago, QuaTTro said:

Yeah we did find that we had overfilled some during this last test day, so that would've been part of the problem.  Plus the direction of the track that day has hard, steep uphill off camber corner that would push the oil in the direction of the breather hose.

Being a seasoned Car I would like to ask:What is different about your catch can or crankcase ventilation system since this trouble has started?

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1 hour ago, Team Infiniti said:

Being a seasoned Car I would like to ask:What is different about your catch can or crankcase ventilation system since this trouble has started?

 

We never ran a catch can before.  We used to run the crankcase ventilation back into the Intake like OEM.  One thing we wondered about last night after completing the compression/leakdown tests was that maybe that crankcase ventilation pipe was routed too low (flat) and oil is no longer running back down into the crankcase.  its almost like its behaving like a sink plumbing trap we suspect.  So now we're raising the angle on that and trying again.

 

The reason we're running the catch can now is that for this race we went to standalone ECU, DIY wiring harness (fun!), intake manifold and MAFless Intake piping (MAF not needed with standalone).

Edited by QuaTTro
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Ideally you want to vent from somewhere that has baffles before it leaves the engine as this will cut down on most of the oil.  In addition to this, if there is room, go vertical immediately after leaving the engine and use the largest hose that is practical.  Vertical section reduces the chances of cornering G's forcing oil out and allows more drain-back.  The large hose reduces the amount of pressure that can build up to push the oil along.

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  • 1 month later...

We have had issues in the past. I played around a bit with a head in a parts washer to see what was going on. With the BMW m30 slanted at 30 degrees, the issue is oil pooling in the head. When corning right at 1 G. The engine experiences a G vector similar to 15 degrees leaned over to the left (30-45). So imagine laying the head over 15 degrees left. On the M30 the drain passages are on the right side, so oil will pool. Now reverse the turn to a left 1 G corner. The engine now experiences a G vector similar to 75 degrees leaned over to the right (30+45). So imagine laying the head over 75 degrees right. The vertical oil drain back passages only have a 15 degree downhill for the oil to travel back to the sump. So the oil that had been pooling now has to drain at a fairly horizontal angle which likely drains slowly. The result is likely 1 qt of oil being thrown around in the head, and why its critical for these motors to be a qt over full when racing. Easy for it to be blown out of the breather. Our solution was simple. We just raised up the valve cover oil fill cap and stuck a breather on it so it was up high. Oil blowing out the breather was reduced quite a lot.

 

Check out the video I made showing what the oil does in an M30: 

 

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27 minutes ago, Jim said:

We have had issues in the past. I played around a bit with a head in a parts washer to see what was going on. With the BMW m30 slanted at 30 degrees, the issue is oil pooling in the head. When corning right at 1 G. The engine experiences a G vector similar to 15 degrees leaned over to the left (30-45). So imagine laying the head over 15 degrees left. On the M30 the drain passages are on the right side, so oil will pool. Now reverse the turn to a left 1 G corner. The engine now experiences a G vector similar to 75 degrees leaned over to the right (30+45). So imagine laying the head over 75 degrees right. The vertical oil drain back passages only have a 15 degree downhill for the oil to travel back to the sump. So the oil that had been pooling now has to drain at a fairly horizontal angle which likely drains slowly. The result is likely 1 qt of oil being thrown around in the head, and why its critical for these motors to be a qt over full when racing. Easy for it to be blown out of the breather. Our solution was simple. We just raised up the valve cover oil fill cap and stuck a breather on it so it was up high. Oil blowing out the breather was reduced quite a lot.

 

Check out the video I made showing what the oil does in an M30: 

 

Awesome analysis.  thanks.

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