OBD-II CEL : Carbon buildup issues (long)
10-11-2003, 12:31 AM
#77
You 993 guys continually fail to get the points:
I never said that the valve guide material being used by Porsche
was optimized for max wear and min long term oil consumption.
They are probably using the present material for other factors.
Because of this material and it's wear pattern, compounded with
the design of the secondary air inlet to the exhaust port, OBDII
problems occur. This was stated early on by me on the other thread,
when many posts were trying to understand the problem.
My second point was that wear is a function of friction. The total
amount of wear (loss of guide material) over time results from the
total continuous valve travel over. If the valve travels a 10mm
to open and then 10mm to close, then it has travelled 20mm per
every 2 revolutions of the engine. Therefore, more revolutions
per unit time (rpm) results in more valve travel per unit time, which
causes more total friction on the valve guide and thus more wear.
I never stated that high reving was the only cause of valve guide
wear, but only that it helps to accelerate it over time. In a perfect
world with zero valve and guide friction, there would be no guide
wear. So, find the perfect oil which results in zero friction and you'll
have no wear.
I've tried to explain what's been stated as simple as possible.
If someone has a better explanation for the valve guide wear,
i.e. the fundamental CAUSE, then please present it. Don't say
that it's bad material, because we all accept the fact that any
material will exhibit wear over time. Obviously, a different material
could be used to minimize wear and extend the time for a valve job.
What factor, other than friction, is causing the wear and as such
is unrelated to total valve travel based on rpm? A simple given
and starting point which we all accept (I hope) is that zero rpm
results in zero wear.
So, please logically prove that valve guide wear is unrelated to
rpm, i.e. total valve travel over TIME does not cause a total
combined friction in the guide resulting in wear.
Thanks
Loren
'88 3.2
I never said that the valve guide material being used by Porsche
was optimized for max wear and min long term oil consumption.
They are probably using the present material for other factors.
Because of this material and it's wear pattern, compounded with
the design of the secondary air inlet to the exhaust port, OBDII
problems occur. This was stated early on by me on the other thread,
when many posts were trying to understand the problem.
My second point was that wear is a function of friction. The total
amount of wear (loss of guide material) over time results from the
total continuous valve travel over. If the valve travels a 10mm
to open and then 10mm to close, then it has travelled 20mm per
every 2 revolutions of the engine. Therefore, more revolutions
per unit time (rpm) results in more valve travel per unit time, which
causes more total friction on the valve guide and thus more wear.
I never stated that high reving was the only cause of valve guide
wear, but only that it helps to accelerate it over time. In a perfect
world with zero valve and guide friction, there would be no guide
wear. So, find the perfect oil which results in zero friction and you'll
have no wear.
I've tried to explain what's been stated as simple as possible.
If someone has a better explanation for the valve guide wear,
i.e. the fundamental CAUSE, then please present it. Don't say
that it's bad material, because we all accept the fact that any
material will exhibit wear over time. Obviously, a different material
could be used to minimize wear and extend the time for a valve job.
What factor, other than friction, is causing the wear and as such
is unrelated to total valve travel based on rpm? A simple given
and starting point which we all accept (I hope) is that zero rpm
results in zero wear.
So, please logically prove that valve guide wear is unrelated to
rpm, i.e. total valve travel over TIME does not cause a total
combined friction in the guide resulting in wear.
Thanks
Loren
'88 3.2
10-11-2003, 01:02 AM
#78
Followup: A good example of what I've stated is the Waybrig post
in which he states that the oil consumption increased with hard
driving.
Steve states that the engine's rings aren't fully seated, which
failed to address the FUNDAMENTAL cause (hard driving). The
fact that the rings haven't seated (or whatever) still exists
when the car is NOT driven hard and the oil consumption is
less. The only variable is rpm.
Simple logic proves the relationship of high rpm and high oil
consumption no matter where it comes from, e.g. rings, valve
guides, bad cylinder walls, etc.
How much clearer can it be stated? The guy drives lightly with
little to no noticeable comsumption over a time period. He then
drives hard and adds .5 quart sooner than normal.
Have Fun
Loren
'88 3.2
in which he states that the oil consumption increased with hard
driving.
Steve states that the engine's rings aren't fully seated, which
failed to address the FUNDAMENTAL cause (hard driving). The
fact that the rings haven't seated (or whatever) still exists
when the car is NOT driven hard and the oil consumption is
less. The only variable is rpm.
Simple logic proves the relationship of high rpm and high oil
consumption no matter where it comes from, e.g. rings, valve
guides, bad cylinder walls, etc.
How much clearer can it be stated? The guy drives lightly with
little to no noticeable comsumption over a time period. He then
drives hard and adds .5 quart sooner than normal.
Have Fun
Loren
'88 3.2
10-11-2003, 01:26 AM
#79
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Originally posted by Lorenfb
Followup: A good example of what I've stated is the Waybrig post
in which he states that the oil consumption increased with hard
driving.
Steve states that the engine's rings aren't fully seated, which
failed to address the FUNDAMENTAL cause (hard driving). The
fact that the rings haven't seated (or whatever) still exists
when the car is NOT driven hard and the oil consumption is
less. The only variable is rpm.
Simple logic proves the relationship of high rpm and high oil
consumption no matter where it comes from, e.g. rings, valve
guides, bad cylinder walls, etc.
How much clearer can it be stated? The guy drives lightly with
little to no noticeable comsumption over a time period. He then
drives hard and adds .5 quart sooner than normal.
Have Fun
Loren
'88 3.2
Followup: A good example of what I've stated is the Waybrig post
in which he states that the oil consumption increased with hard
driving.
Steve states that the engine's rings aren't fully seated, which
failed to address the FUNDAMENTAL cause (hard driving). The
fact that the rings haven't seated (or whatever) still exists
when the car is NOT driven hard and the oil consumption is
less. The only variable is rpm.
Simple logic proves the relationship of high rpm and high oil
consumption no matter where it comes from, e.g. rings, valve
guides, bad cylinder walls, etc.
How much clearer can it be stated? The guy drives lightly with
little to no noticeable comsumption over a time period. He then
drives hard and adds .5 quart sooner than normal.
Have Fun
Loren
'88 3.2
Engine Oil Consumption
If the vehicle is used for repeated short trips, and consumes a normal amount of oil, the dipstick may not show any drop in the oil level at all, even after 600 miles or more. This is because the oil is gradually becomming diluted with fuel or moisture, making it appear that the oil level has not changed. The diluting ingredients evaporate out when the vehicle is driven at high speeds, making it appear that oil is excessively consumed after driving at high speeds.
10-11-2003, 01:32 AM
#80
Another Followup:
If there were no other posts except what Waybrig tells us,
(higher oil consumption with hard driving), and we know that oil consumption (burning oil) generates carbon, and that carbon
causes secondary air injection problems, what can we conclude?
He (Waybrig) has basically provided the answer, where
six pages or more of posts couldn't.
Have Fun
Loren
'88 3.
If there were no other posts except what Waybrig tells us,
(higher oil consumption with hard driving), and we know that oil consumption (burning oil) generates carbon, and that carbon
causes secondary air injection problems, what can we conclude?
He (Waybrig) has basically provided the answer, where
six pages or more of posts couldn't.
Have Fun
Loren
'88 3.
10-11-2003, 01:50 AM
#81
Based on what Reilly posts, Waybrig should have been a half
quart higher in the long run. He doesn't state this anomaly when
he resumed normal driving and checked the oil later.
Have Fun
Loren
'88 3.2
quart higher in the long run. He doesn't state this anomaly when
he resumed normal driving and checked the oil later.
Have Fun
Loren
'88 3.2
10-11-2003, 11:07 AM
#82
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Join Date: Jan 2003
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Kevin: Thanks for the post, it's amazing what you can learn by reading the F'ing manual.
Here's my interpretation of what was happening to me, solely based on what the manual says:
I hadn't given the car a good workout for several weeks before my autocross. During that time the car was consuming oil as normal, but this was masked by contaminants building up. Then, during the autocross the contaminants evaporated out as the engine was operated at higher temperature, higher RPM's. Those contaminants evaportating gave the impression that I actually consumed a large quantity of oil during the autocross. Assuming the contaminants evaporated and were cleared from the system, they didn't return when the engine cooled. Therefore I needed to add 1/2 quart of oil.
So, in the big picture, will any of this change my driving habits? No.
As with everything in life you can find an "expert" to support pretty much any position so we each have to use our own judgement to decide our course of action.
Logically to me, running an engine at high RPM's does cause components to wear faster than running at low RPM's. At the same time, running at low RPM's could cause problems with buildup of carbon, etc... that the higher RPM's and temps should clean out. So, when owning a sports car which was designed to run at high RPM's in the first place I'm willing to risk a little premature wear in the interest of keeping things hopefully running cleaner, and having more fun as the builders intended.
Here's my interpretation of what was happening to me, solely based on what the manual says:
I hadn't given the car a good workout for several weeks before my autocross. During that time the car was consuming oil as normal, but this was masked by contaminants building up. Then, during the autocross the contaminants evaporated out as the engine was operated at higher temperature, higher RPM's. Those contaminants evaportating gave the impression that I actually consumed a large quantity of oil during the autocross. Assuming the contaminants evaporated and were cleared from the system, they didn't return when the engine cooled. Therefore I needed to add 1/2 quart of oil.
So, in the big picture, will any of this change my driving habits? No.
As with everything in life you can find an "expert" to support pretty much any position so we each have to use our own judgement to decide our course of action.
Logically to me, running an engine at high RPM's does cause components to wear faster than running at low RPM's. At the same time, running at low RPM's could cause problems with buildup of carbon, etc... that the higher RPM's and temps should clean out. So, when owning a sports car which was designed to run at high RPM's in the first place I'm willing to risk a little premature wear in the interest of keeping things hopefully running cleaner, and having more fun as the builders intended.
10-11-2003, 01:13 PM
#83
Originally posted by Kevin Reilly
How much clearer can it be stated? How about if I read from page 97 of the 993 owners manual. I'm sure the same language is in your 3.2 manual:
Engine Oil Consumption
If the vehicle is used for repeated short trips, and consumes a normal amount of oil, the dipstick may not show any drop in the oil level at all, even after 600 miles or more. This is because the oil is gradually becoming diluted with fuel or moisture, making it appear that the oil level has not changed. The diluting ingredients evaporate out when the vehicle is driven at high speeds, making it appear that oil is excessively consumed after driving at high speeds.
How much clearer can it be stated? How about if I read from page 97 of the 993 owners manual. I'm sure the same language is in your 3.2 manual:
Engine Oil Consumption
If the vehicle is used for repeated short trips, and consumes a normal amount of oil, the dipstick may not show any drop in the oil level at all, even after 600 miles or more. This is because the oil is gradually becoming diluted with fuel or moisture, making it appear that the oil level has not changed. The diluting ingredients evaporate out when the vehicle is driven at high speeds, making it appear that oil is excessively consumed after driving at high speeds.
This is a long thread -- has anyone mentioned using a leak-down test to diagnose engine wear? Or a simple compression test on easily accessible cylinders?
My 993 Turbo gets started every week or so for a "spirited" run in the country or it gets trailered to a track and does some hard work but never sees the redline much less the rev-limiter.
It has 11,000 miles.
On a cold startup after sitting for a week, it will belch out a cloud (sometimes it doesn't make any smoke and when it does, it's invariably from only one bank) and then it settles down and won't make another "fart" until it's left sit for days.
My engine uses no oil. Meaning, I've driven it from 9500 miles to 11,500 as described and the oil level is constant. I also have the oil a little above 3/4 of the twists. This, I suspect, contributes to the smoking. I'm going to drain it down to 1/4 and see what happens.
I've been expecting that the oil getting burned on startup will sooner or later take effect on the dipstick (not me, the measuring device) and I'll see some oil consumption. Certainly with 2000 miles there should be some change. Not so far. And I don't think my driving patterns in this car fit the "fuel and water in the oil" scenario in the owner's manual.
The car just did two days at Buttonwillow. Consumables were front pads and rear tyres ... around 60 laps per day ... and four tanks of gas at $5/gal averaging about 5mpg ... OUCH ...
Last edited by Carrera GT; 10-11-2003 at 01:34 PM.
