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JohnJL's Avatar
 
Join Date: Jan 2005
Location: Toronto, Ontario
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Overflow oil tank is puffing smoke

I am trying to diagnose and deal with a problem thats always been there but has gotten noticably worse recently. The motor has a season on it, and wasnt stessed hard, there no reason it should be acting differently so I wonder if I just didnt notice it so bad before or if anything has changed.

The motor is a 3.2l supercharged running ~12psi or .9 bar.

I have a 2+ litre overflow tank plumbed off the oil filler neck. It has a filter on the top, and it drains to the 4-5-6 upper valve cover. It does not fill up with oil, but it does puff smoke out the filter with each cylinder firing. I took the filter off the overflow tank vent and see it clearly puff. If I block that filter hole and open the oil filler neck, it puffs out there with each cylinder firing.

The smoke is prolofic. I need to do some better sealing of the firewall to the cabin, so I get lots of smoke in the cabin now, particularly shortly after I come off full throttle and get back into it after a corner. Even when the cabin is fully sealed, I cant have that smoke coming off the back. The filter on the overflow tank tends to cool/collect the oil vapor and it drips down in the engine compartment and on the headers. Very stinky and smokey.

Firstly, I am not sure why this is happening and if it indicates a problem. Right now I have the normal oil line coming off the oil filler neck to the engine case. I also have that same filler neck venting to the overflow tank, which is the one smoking like crazy. Should I be plumbing this differently?

I scanned a couple of alternatives, not sure if these would help. Both are variations on feeding that smoking bent back into the intake. The obvious downside being I would now be feeding my engine intake with oil vapor which cant be great.

Anyone help with diagnosis of whats happening, why, and what I should do?

If I do plumb it into the intake, seems it would need to feed in before the throttle body, right? Option 2 below would seem to bleed an unlimited leak after the throttle body, which would essentially be a major intake leak.

Thanks!





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Old 05-12-2013, 04:59 PM
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One thing that what you describe can be a sign of (which you won't want to hear/read) is excessive blowby into the crankcase (as in broken rings). Of course, you would have to do a leakdown test to make sure.

Isn't .9 bar much too high boost pressure for a 3.2's static compression ratio? That would explanin the broken rings (provided that is your problem).

Last edited by Ronnie's.930; 05-12-2013 at 06:28 PM..
Old 05-12-2013, 05:47 PM
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A holed piston in a Porsche makes a lot of smoke under the circumstances you describe. No odd noises and no sudden loss of power.
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Old 05-12-2013, 06:19 PM
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The pistons are fairly new 8:1 JE coated pistons with dual plugs and knock control (though I've never had pinging register except when tapping the block with drift to check if its working). Its possible I have a broken ring as I havent checked leakdown recently.
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2007 911 Turbo - Not a toy
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1982 911 3.2 Indiash Rot Track Supercharged track toy
1978 911 3.0 Lichtbau toy "Gretchen"
1971 911 Targa S backroad toy
Old 05-12-2013, 06:34 PM
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If the oil smoke/vapor is coming out of the crankcase in the manner you describe, then you have a blowby problem. Have you tried running the engine with the crankcase vent hose removed from the oil tank to check for smoke from there (isolate the source of the smoke)?

Old 05-12-2013, 07:00 PM
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