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"I am the liquor..."
 
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Question An interesting oil consumption observation

...need to file this one under things that make you go "HHHMMM"...

I've come across an interesting oil consumption phenomenon with my engine and was looking for some feedback and/or your own experiences.

My car/engine seems to like the oil level being maintained at the low end of the dipstick. If I try to keep the oil level at the "half way" mark, my consumption goes up considerably until she reaches her place further down the stick. Once there, the consumption pretty much stops. Here is some additional info:

-Very rare smoke at start-up - if there is any, it goes away immediately.
-Absolutely no leaks (knock wood).
-No smoke on accel or decel.
-Using Brad Penn 20W-50.
-After market headers with the small "un-vented" turbo drip tank (factory tank had a vent up to the air box).
-Factory airbox removed, and the hose that connected the crank case ventilation system to the airbox now just has a small air filter on the end.
-My dipstick and oil level gauge match perfectly; both read the same.
-Daily driver, no track and/or DE time.
-Just over 10,000 miles on a total rebuild.
-Engine has NEVER been overfilled with oil.
-I'm well versed in how to check oil in these engines.

I've noticed that when my oil level is at the half way mark (maybe a tad more), there is more smoke/steam/mist coming from the oil filler neck. When the level is down, this steam is mostly non-existent.

I got concerned because in less than three hundred miles I saw my level gauge go from a hint over half way, to a few milimeters above the bottom line. I thought maybe I had cracked some rings during all of the tuning that I've done, to steady state my CIS system, and was experiencing some blow-by. But now not a drop is being used (yes there is oil in the engine ). I will take a hot leakdown and compression test soon...I'm just soooo busy at work and with holidays, I haven't had a chance.

Furthermore, in a few of the oil consumption threads that I read through, a couple users mentioned that their engines also liked a particular oil level...once there, all was good.

I've been told by a few "Porsche engine masters", that the crank case ventilation system in these engines is hideously poor. I wonder if no longer having a turbo sump tank vent is a contributing factor?
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Last edited by sand_man; 12-12-2007 at 07:07 AM..
Old 12-12-2007, 07:01 AM
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One other thing I wanted to mention is that it's been hard for me to really track the consumption. I've been on a roll of testing various oil brands and viscosities. I know this is'nt always a good thing to do, but I'm completely happy with the Brad Penn, and this is the only oil that I'll now run.

Additionally, I think I had some fuel/oil dilution going on when I experienced some issues with my fuel head, that have now been fixed. I'm sure this didn't help consumption, either.

This next oil change will be very telling...
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Last edited by sand_man; 12-12-2007 at 07:09 AM..
Old 12-12-2007, 07:06 AM
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I dont think your turbo drip tank has any bearing on this. With the aftermarket headers- do you have the stock oil line or the braided one going to your t-stat from the motor? I have seen issues before with those but not with oil consumption. I dont think you have much to worry about- even on the low end of the dipstick there is still 9 quarts in there. On the newer oil tanks it is standard practice on oil change to put 8 quarts in, start and top off.
Maybe the turbo and its location after the new headers plays a roll- I know its stock location- but it does change a little. Maybe there is a little more pressure on it when there is a higher oil level in the tank/engine. I doubt it has anything to do with your bottom end as that should be about as tight as a dolphin's @$$
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Last edited by 930gt-40r; 12-12-2007 at 07:26 AM..
Old 12-12-2007, 07:23 AM
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Quote:
Originally Posted by sand_man View Post
...need to file this one under things that make you go "HHHMMM".............

My car/engine seems to like the oil level being maintained at the low end of the dipstick. If I try to keep the oil level at the "half way" mark, my consumption goes up considerably until she reaches her place further down the stick.
Hmmmm....no not all. I have noticed the same thing and doing the same thing as you. Keeping it at the low end.

If you have the same type of oil tank breather system as mine-----which is not much, it could be the cause of the problem. I have the oil tank breather line going to the intake of the air cleaner.

My Theory:
The oil tank on dry sump systems is a turbulent place. When the oil is returned from the dry sump pumps, it is under good pressure and creates some splashing of oil (plus some foaming) on the tank walls. I think the breather line is sucking up some oil droplets into the intake.

I'm going to try this theory out in the Spring when I add a breather tank with oil separator to the breather line.
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Old 12-12-2007, 07:40 AM
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My '87 does have the factory oil separator. Currently, I have a hose that runs from the top of the crank case to the separator, a hose that runs from the filler neck to the separator, and the final hose is what connected the separator to the airbox - on this hose, I have a small air filter fitted. Additionally, the bottom of the separator drains any oil back to the oil tank.

I'm afraid that if I install my factory airbox and connect that hose to the separator, that I'll be sucking those oil droplets, that you mentioned, into the intake.
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back in the saddle: '95 993 - just another black C2
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Old 12-12-2007, 08:50 AM
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My car is similar in that it seems to use oil from the top mark a little quicker that the oil near the bottom mark - seems backwards now that I think about it but the usage is well within normal limits and my motor is over 120k miles.
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Old 12-12-2007, 09:05 AM
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I thought my 930 was the only one!

Mostly stock motor with 40k original miles on it with a FMOC and no oil leaks.
Complete oil drain and refill with 11 qts Mobil 1 15-30.
Oil tank level will be at full and within 200 miles needle will be right above the low mark where it will stay until next oil change...weird!
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Old 12-12-2007, 09:14 AM
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Ditto, my car has the same behavior. It looks like a little low is the right level. After reading this I'll stop chasing the oil level on mine. I am currently monitoring consumption with the reset odometer. I'm at 738 miles and I've dropped from the center of the gauge to just above the red. I've never seen it go below that. (level always checked @ 210 degrees, idling on level ground, blah, blah, you know the routine.)
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Old 12-13-2007, 07:16 AM
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Quote:
Originally Posted by sand_man View Post
My '87 does have the factory oil separator. Currently, I have a hose that runs from the top of the crank case to the separator, a hose that runs from the filler neck to the separator, and the final hose is what connected the separator to the airbox - on this hose, I have a small air filter fitted. Additionally, the bottom of the separator drains any oil back to the oil tank.

I'm afraid that if I install my factory airbox and connect that hose to the separator, that I'll be sucking those oil droplets, that you mentioned, into the intake.
Sandman,
I take it that you have the KKK turbo in your car? Other than oil consumption through the rings, the only other place where oil could get in your engine would be the turbocharger seals. Do you have aftermarket headers? If you do, I suspect the culprit may be the turbo sump pump system. I have read that the sump pump for the turbocharger is very inefficient at idling speeds. So if you are cooling the turbo down after a long drive by letting it idle, the oil will not be scavenged from the tank. Try keeping the revs around 2K RPM for 30 seconds before shutting off the engine. It made a world of difference on mine. No smoke on startup since I started this practice.
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'85 930 Factory Special Wishes Flachbau
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Old 12-13-2007, 08:18 AM
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Quote:
Originally Posted by WERK-I View Post
Sandman,
I take it that you have the KKK turbo in your car? Other than oil consumption through the rings, the only other place where oil could get in your engine would be the turbocharger seals. Do you have aftermarket headers? If you do, I suspect the culprit may be the turbo sump pump system. I have read that the sump pump for the turbocharger is very inefficient at idling speeds. So if you are cooling the turbo down after a long drive by letting it idle, the oil will not be scavenged from the tank. Try keeping the revs around 2K RPM for 30 seconds before shutting off the engine. It made a world of difference on mine. No smoke on startup since I started this practice.
Yes, I have the K27HFS turbo and OBX headers. That's good info regarding the inefficency of the scavenge pump.

And to answer another question from 930gt-40r about the oil line that runs up to the T-stat from the crank case, I have the braided one. I do have plans to replace this hose with the hard pipe that has a horse-shoe shape to it, to fit under the bell housing, but as with anything, I just haven't had time.
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back in the saddle: '95 993 - just another black C2
*SOLD*: '87 930 GP White - heroin would have been a cheaper addiction...
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Old 12-13-2007, 08:48 AM
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My 930 does this as well. I had the car for two weeks before it blew up, so 10k on a rebuilt engine. I always got a cloud of smoke on start up when the oil level was at the upper end of full. when the oil level would get low I'd quit getting smoke on start up and would get worried because the guage would be in the red sometimes untill full warmed up. but now that you've brought this to light, I'll just leave it at the low level and let it roll. thankyou.
Old 12-13-2007, 06:18 PM
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If they would have understood the dynamics of the turbo oiling system then maybe the vent less aftermarket turbo sump tank would have never been born…

Turbo cars are going to eat some oil. The amount of oil flowing over the turbo bearing is substantial especially at high engine RPM’s - gasses are created as part of the bearing lubrication/cooling process. There is also a measure of cross flow of gasses from the hot and cold side of the turbo which escape past worn bearing seals into hot and cold side as well as the oil dump outlet on the bottom of the turbo which is connected to the sump tank.

Enter the turbo vent pipe on the factory tank. During periods of sustained peak boost at high engine RPM’s, one could easily envision oil in the sump being backed up into the vent tube, into the oil breather hose with some quantity oil/oil vapors being sucked into the air box (although the factory air box is big, the vacuum created by the turbo on the filter side is tremendous and will quickly overcome the filter’s rated flow capacity thus causing other circuits to normalize that lack of adequate flow- the turbo vent/breather tube being one of them).

The case of the “missing motor oil” could easily be attributed to worn turbo bearing seals, a weak scavenge pump which is out of spec, the addition of a larger turbo with an increased flow rate across the bearing surface, an improperly sized sump tank. The possibilities are myriad.

Anyway, that’s my take

Munchovie.
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Old 12-14-2007, 07:34 PM
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................I'd quit getting smoke on start up and would get worried because the guage would be in the red sometimes untill full warmed up. but now that you've brought this to light, I'll just leave it at the low level and let it roll. thankyou.
I believe there's a choir out there somewhere that could do this in harmony, but here goes------ "Never Trust the Gauge!". If ever there was a gauge that we 911 owners could do without, it's the oil level gauge.
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Old 12-15-2007, 07:39 AM
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Quote:
Originally Posted by WERK-I View Post
I believe there's a choir out there somewhere that could do this in harmony, but here goes------ "Never Trust the Gauge!". If ever there was a gauge that we 911 owners could do without, it's the oil level gauge.
I assumed you guys were talking about the dip stick.. I've had the guage hover on the low side only to find it took three quarts to get it back to where it belonged... With the guage anything but an on level mid range reading isn't even close to accurate.
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Old 12-15-2007, 08:35 AM
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