Cloud of smoke/oil leak
10-21-2002, 04:07 PM
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Cloud of smoke/oil leak
I had posted earlier about this situation. 1981 928 with all testing completed, i.e. leakdown, compression ,emissions, breather, etc. This car is with a very competent Porsche mechanic that is baffeled. The car can be reved to high limits,5500-6000, in the garage stationary or with the car in gear , wheels spinning. No smoke or leaks. Take the car on the road and in any gear floor it to high revs, it blows smoke and begins immediately to leak. If one drives the car in any gear up to about 4500-5000 RPM, in a slow fashion, meaning the accellerator is not floored.....no smoke. The leak was originally traced and thought to be a head gasket. It was replaced and still has this problem. Any help at this time is appreciated.
10-21-2002, 04:44 PM
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Doc,
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Take the car on the road and in any gear floor it to high revs, it blows smoke and begins immediately to leak.
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What do you mean with .. and begins immediately to leak?
Do you get oil leak from the engine? If yes from where?
Are you sure your 'leak down' test was posetive?
------
Take the car on the road and in any gear floor it to high revs, it blows smoke and begins immediately to leak.
------
What do you mean with .. and begins immediately to leak?
Do you get oil leak from the engine? If yes from where?
Are you sure your 'leak down' test was posetive?
10-21-2002, 05:26 PM
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More a sign of poor ring sealing. Maybe a partially plugged crankcase vent system too. Weak rings will do OK with no load, but will leak by more when there is some load on them. In addition, the extra blowby will add pressure to the crankcase, increasing the flow of vapors into the intake of the engine.
A compression test should give you a hint of which cylinders are causing the most problems. A good leakdown will confirm that the flow path is past the rings to the crankcase.
Good luck!
A compression test should give you a hint of which cylinders are causing the most problems. A good leakdown will confirm that the flow path is past the rings to the crankcase.
Good luck!
10-21-2002, 08:49 PM
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I have had a similar problem before.
It seems that the crankcase pressure gets too high under high loads, and it blows oil past the front seals on the engine, thus getting oil on the headers, and resultant smoke, etc...
Here is my additional question:
Can someone give me a more detailed explanation of the crankcase ventilation system on the 928's? Mine is an 83 Euro. I was wondering if there is a way to test for proper venting, and if there is any way to modify it for better functionality. I keep remembering that Devek may have come up with a workaround, but it also sounded like it involved a blowby tank, and a lot of complex stuff. Is there a way to simply do a breather the way they do on race cars? Basicly a small air cleaner vented to each valve cover? Or something like that?
It seems that the crankcase pressure gets too high under high loads, and it blows oil past the front seals on the engine, thus getting oil on the headers, and resultant smoke, etc...
Here is my additional question:
Can someone give me a more detailed explanation of the crankcase ventilation system on the 928's? Mine is an 83 Euro. I was wondering if there is a way to test for proper venting, and if there is any way to modify it for better functionality. I keep remembering that Devek may have come up with a workaround, but it also sounded like it involved a blowby tank, and a lot of complex stuff. Is there a way to simply do a breather the way they do on race cars? Basicly a small air cleaner vented to each valve cover? Or something like that?
10-22-2002, 08:01 AM
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Erik: The car actually is thought to lose oil externally around the right cylinder head gasket area which then drops onto the header system and smokes/burns off. The car has excellant compression,leakdown testing was that of a new engine. The mechanic thought the leak emminated from the head gasket;therefore the head gasket replacement.The car runs beautifully throughout the RPM range.....its the external oil leak that is the problem. Where is Wally Plummer located so that I can call him? Any other suggestions? Thanks for the help to everyone.
10-22-2002, 10:22 AM
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The early 928 engine vent system as described by Porsche:
"Blow-by is routed from the crankcase to an oil seperator were (sic) any oil carried along can settle and flow back to the oil pan.
The blow-by continues fromt he oil separator to the lower section of the air cleaner. A preheating line runs over a short portion of the vent hose. a flame guard (arrow) is installed in the inlet adaptor on the lower section of the air cleaner. The oil separator is also used as an oil filler."
Your problem may be the cumulative result of more than one cause. Most 928s suffer from an inadequate crankcase ventilation system under full-throttle, high-RPM conditions.
After twenty years, the piston rings are a bit worn, and have also lost some of their tension. Even though the piston/wall setup on a 928 is very likey the best that has ever been used on a production automobile, you will eventually get increased blow-by at high-load, high-RPM operation.
The valve guides and stems also wear, and the valve stem seals get hard and worn, adding significantly to the blow-by.
The usual problem is that high blow-by gas flow carries excessive engine oil into the intake system, causing high oil consumption, possible detonation, carbon build-up on the valves and chamber, and higher emissions.
It is also common for the vent hoses in the engine vee to fail, filling the vee with oil. This should have been found and fixed during the head gasket replacement.
In your case, the high blow-by appears to be overwhelming a seal or gasket on the cam housing. My suggestion is to clean the area as completely as possible, and then add UV dye to the oil, run the car hard one time, and use a UV lamp to find the oil leak.
If your mechanic doesn't have the UV equipment, you can clean the area, and blow talcum power over the surface. Run the car hard one time, and look for the leakage pattern. There are few possible leakage areas - the gasket at the rear of the housing, the cam seal on the front, the plugs on top, and the head gasket.
There may be another contributing factor. If the oil drain-back holes in the cylinder head are partially plugged, you may be filling the cam housing with oil. This will make leakage much worse. I would have expected this problem, if it existed, to have been found and corrected during the head gasket replacement.
A complete cure will require extensive and expensive engine work, including new piston rings, valve guides and seals as a minimum.
There is not a good, cheap and easy cure. Several owners, mostly racers, have attempted to add vent flow capacity. Results have been mixed - none have announced total success.
Devek offers an oil baffle for the oil filler neck that might help the oil entrainment problem, but probably wouldn't help you.
My only suggestion is to try to find the leak and fix it.
"Blow-by is routed from the crankcase to an oil seperator were (sic) any oil carried along can settle and flow back to the oil pan.
The blow-by continues fromt he oil separator to the lower section of the air cleaner. A preheating line runs over a short portion of the vent hose. a flame guard (arrow) is installed in the inlet adaptor on the lower section of the air cleaner. The oil separator is also used as an oil filler."
Your problem may be the cumulative result of more than one cause. Most 928s suffer from an inadequate crankcase ventilation system under full-throttle, high-RPM conditions.
After twenty years, the piston rings are a bit worn, and have also lost some of their tension. Even though the piston/wall setup on a 928 is very likey the best that has ever been used on a production automobile, you will eventually get increased blow-by at high-load, high-RPM operation.
The valve guides and stems also wear, and the valve stem seals get hard and worn, adding significantly to the blow-by.
The usual problem is that high blow-by gas flow carries excessive engine oil into the intake system, causing high oil consumption, possible detonation, carbon build-up on the valves and chamber, and higher emissions.
It is also common for the vent hoses in the engine vee to fail, filling the vee with oil. This should have been found and fixed during the head gasket replacement.
In your case, the high blow-by appears to be overwhelming a seal or gasket on the cam housing. My suggestion is to clean the area as completely as possible, and then add UV dye to the oil, run the car hard one time, and use a UV lamp to find the oil leak.
If your mechanic doesn't have the UV equipment, you can clean the area, and blow talcum power over the surface. Run the car hard one time, and look for the leakage pattern. There are few possible leakage areas - the gasket at the rear of the housing, the cam seal on the front, the plugs on top, and the head gasket.
There may be another contributing factor. If the oil drain-back holes in the cylinder head are partially plugged, you may be filling the cam housing with oil. This will make leakage much worse. I would have expected this problem, if it existed, to have been found and corrected during the head gasket replacement.
A complete cure will require extensive and expensive engine work, including new piston rings, valve guides and seals as a minimum.
There is not a good, cheap and easy cure. Several owners, mostly racers, have attempted to add vent flow capacity. Results have been mixed - none have announced total success.
Devek offers an oil baffle for the oil filler neck that might help the oil entrainment problem, but probably wouldn't help you.
My only suggestion is to try to find the leak and fix it.
10-22-2002, 01:53 PM
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Doc,
Wally said all what to say about your problem, and I agree 100%
I can add, I damaged two engines due to this oil lifting effect - oil goes to the inlet of the engine, this lower the octane value and you get detonation and in worse condition (like mine, during long fast driving in Germany) the detonation brake your piston rings and ring lanes + scratches the cylinder walls - My top ring on #4 was broken down to 2mm small pieces!
Now I have installed, the Devek oil baffle and one extra oil separator (cyclone) and run max 5500 RPM
See the article about Oil driven detonation on Devek Tech Tips <a href="http://www.Devek.net" target="_blank">www.Devek.net</a>
Wally said all what to say about your problem, and I agree 100%
I can add, I damaged two engines due to this oil lifting effect - oil goes to the inlet of the engine, this lower the octane value and you get detonation and in worse condition (like mine, during long fast driving in Germany) the detonation brake your piston rings and ring lanes + scratches the cylinder walls - My top ring on #4 was broken down to 2mm small pieces!
Now I have installed, the Devek oil baffle and one extra oil separator (cyclone) and run max 5500 RPM
See the article about Oil driven detonation on Devek Tech Tips <a href="http://www.Devek.net" target="_blank">www.Devek.net</a>
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10-24-2002, 09:03 AM
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The mechanic found the leak between the first and second cylinders,pass.side,in the block. He said the oil was mist-like at very high revs at what seems to be a stress crack ,very, very small in a casted corner of the block. The fix was a high temp silicone after a thorough cleaning. I just got the car back and it seems to be OK. I thought a weld or epoxy would be better , but the location of the crack(for the lack of a better term), made an in the car repair impossible. What are your thoughts as to the repair, why this happened, etc. Has this happened to anyone else? As noted, I do not like any seepage/leaks of any kind. By the way, the car runs beautifully!
10-24-2002, 10:28 AM
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Doc,
Never heard this before - You said your mechanic changed the head gaskets, was that the same side (#5-#8)?
One possibility for such crack, is if you turn a bolt into a threaded hole filled with oil - The hydraulic effect will then crack the block!
But, this has nothing to do with the smoke at high RPM except the smoke comes from the engine compartment and not from the exhaust.
I doubt, high temperature silicone can seal the crack permanently
Never heard this before - You said your mechanic changed the head gaskets, was that the same side (#5-#8)?
One possibility for such crack, is if you turn a bolt into a threaded hole filled with oil - The hydraulic effect will then crack the block!
But, this has nothing to do with the smoke at high RPM except the smoke comes from the engine compartment and not from the exhaust.
I doubt, high temperature silicone can seal the crack permanently
10-28-2002, 09:22 AM
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I spoke with Jim @928 Int,l , he stated that he has heard of this problem with other 928 blocks. They have a casting problem that allows the loss of oil because of improper adhesion in the aluminum casting of the hot Aluminum. The fix is JB WELD, as this area is not subjected to high pressure. It seems to work well according to Jim. As said, my car was fixed with HT silicone.....hope it lasts. If it were not so old, Porsche should pay to replace the block!!! Wishful thinking. 
10-28-2002, 02:38 PM
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Doc,
Thank you for the info.
The fix from Jim sound reasonable, if 928 International has experience in this welding better to let them do it ASAP - I would not dare to drive with silicone sealing - Imagine one day you drive fast and long and leaking is starting again - Uha!!
Thank you for the info.
The fix from Jim sound reasonable, if 928 International has experience in this welding better to let them do it ASAP - I would not dare to drive with silicone sealing - Imagine one day you drive fast and long and leaking is starting again - Uha!!
