excessive oil blow out....
#1
Three Wheelin'
Thread Starter
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on the '82 928S rally car build i have excessive oil out of the tower... sandwich plate under the tower and catch tank ... still it blows the oil out. 10 dyno runs was good for 1 L oil under the car ....![banghead](https://rennlist.com/forums/graemlins/banghead.gif)
what can be the reason ?
![banghead](https://rennlist.com/forums/graemlins/banghead.gif)
what can be the reason ?
#2
Team Owner
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sounds like excessive blowby,
might be time for fresh rings
might be time for fresh rings
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belgiumbarry (03-24-2021)
#3
Three Wheelin'
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yeah... i was afraid of that .
On the other hand , compression test was perfect .. can that with worn rings ?
On the other hand , compression test was perfect .. can that with worn rings ?
#4
Administrator - "Tyson"
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Detonation can cause blow-by, check your tune and don't always trust knock sensors.
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SwayBar (03-25-2021)
#5
Former Sponsor
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All 928's suffer from the same basic design issue...rpm's put a a lot of oil into suspension and can whip up the oil in the oil pan. The crankcase pressure goes up, effectively blocking the return paths from the cylinder heads. Oil is then held in suspension on the entire top end of the engine. When the crankcase pressure builds to a high enough point, there will be a giant "burp" and the oil gets ejected.
The longer the engine is held at high rpms, the worse the problem gets.
Fortunately, the two valve engines can't "store" as much oil in the heads as the 4 valve engines, so "uncovering" the oil pick-up (sucking air results in almost instant rod bearing damage) is much more rare.
On the other hand, if you study how the two valve engines "vent" the heads, it's quickly obvious that.........they don't.
The first (and most basic thing) to pay attention to is the oil you are running. Steal an electric kitchen mixer (or a hand whisk), heat the oil up, and try to aerate the oil. Some oils are better than others at not aerating.
Most of the "baffles" made to go under the filler neck make the problem worse. The baffle must act like an oil separator when oil in suspension hits it, not block the air/oil once it becomes overwhelmed.
I'm not sure if you have the early oil pan pick-up assembly, in your engine, or not. This design really helps to keep the oil in the oil pan, due to the screen and the cloverleaf pick-up and is definitely a step in the right direction.
Moving the oil away from the crankshaft (pan and pick-up spacer) helps, in conjunction with simple windage trays (when the early oil pick-up assembly is not used.....when the early oil pan pick-up is used, rear windage trays and pan spacer helps.)
Last edited by GregBBRD; 03-24-2021 at 06:28 PM.
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belgiumbarry (03-24-2021)
#7
Three Wheelin'
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i did some tests...
down pipe from oil tower in a oil can and clear vertical plastic hose on the pan tube : oil sure doesn't come higher then the metal tube itself . ( test for crankcase pressure )
And again dripping oil from the catch tank...
Then i let the hose bend from the oil tower vent direct in a cola bottle in the V .... no oil mist ! If it works out that way it is as the long hoses, catch tank etc... give some back pressure and that makes it possible to carry oil mist . Will this test further and ,if so , see for a proper solution. Meanwhile i'm lucky , we have enough empty cola bottles![Smilie](https://rennlist.com/forums/images/smilies/smile.gif)
down pipe from oil tower in a oil can and clear vertical plastic hose on the pan tube : oil sure doesn't come higher then the metal tube itself . ( test for crankcase pressure )
And again dripping oil from the catch tank...
Then i let the hose bend from the oil tower vent direct in a cola bottle in the V .... no oil mist ! If it works out that way it is as the long hoses, catch tank etc... give some back pressure and that makes it possible to carry oil mist . Will this test further and ,if so , see for a proper solution. Meanwhile i'm lucky , we have enough empty cola bottles
![Smilie](https://rennlist.com/forums/images/smilies/smile.gif)
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#8
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i did some tests...
down pipe from oil tower in a oil can and clear vertical plastic hose on the pan tube : oil sure doesn't come higher then the metal tube itself . ( test for crankcase pressure )
And again dripping oil from the catch tank...
Then i let the hose bend from the oil tower vent direct in a cola bottle in the V .... no oil mist ! If it works out that way it is as the long hoses, catch tank etc... give some back pressure and that makes it possible to carry oil mist . Will this test further and ,if so , see for a proper solution. Meanwhile i'm lucky , we have enough empty cola bottles![Smilie](https://rennlist.com/forums/images/smilies/smile.gif)
down pipe from oil tower in a oil can and clear vertical plastic hose on the pan tube : oil sure doesn't come higher then the metal tube itself . ( test for crankcase pressure )
And again dripping oil from the catch tank...
Then i let the hose bend from the oil tower vent direct in a cola bottle in the V .... no oil mist ! If it works out that way it is as the long hoses, catch tank etc... give some back pressure and that makes it possible to carry oil mist . Will this test further and ,if so , see for a proper solution. Meanwhile i'm lucky , we have enough empty cola bottles
![Smilie](https://rennlist.com/forums/images/smilies/smile.gif)
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belgiumbarry (03-26-2021)
#10
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Strosek Ultra (03-26-2021)
#11
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FYI - I just pulled a few ounces of water out of my oil separator that I use on my oil breather system for my turbo charged 928. I collected none in the warm weather, so it was definitely a function of driving it in the cold. If you are plumbing the condensate back into the sump, you're providing no path for water condensate to escape the oiling system. Just something to consider.
#12
RL Community Team
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FYI - I just pulled a few ounces of water out of my oil separator that I use on my oil breather system for my turbo charged 928. I collected none in the warm weather, so it was definitely a function of driving it in the cold. If you are plumbing the condensate back into the sump, you're providing no path for water condensate to escape the oiling system. Just something to consider.
It's one of the main reasons I chose this particular AOS to use since I was plumbing it back to the sump.
![](https://cimg5.ibsrv.net/gimg/rennlist.com-vbulletin/2000x1504/20190804_183137_hdr_a77f57462683f51e5635550f953313562db2247c.jpg)
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Last edited by Petza914; 03-26-2021 at 10:42 AM.
#13
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The heat helps it flow, but doesn't stop water from condensing into your oil. But, since you don't drive it in cold weather it may never become an issue for you. If you do drive it in cold weather, your heated AOS will not prevent water condensate from getting into your oil.
#14
RL Community Team
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The heat helps it flow, but doesn't stop water from condensing into your oil. But, since you don't drive it in cold weather it may never become an issue for you. If you do drive it in cold weather, your heated AOS will not prevent water condensate from getting into your oil.
#15
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Only if there is a place for the water to leave the system. An AOS condenses the water, and it doesn't leave the system. Even if it's heated. Not a huge problem in the summer, but in the winter it builds up significantly. Take it or leave it. Those are the facts.