993 oil consumption
11-12-2018, 08:40 PM
#1
993 oil consumption
I have a 98 C2S with 61K miles. I've been using about a qt. of Mobil1 20-50 every 1900 miles. (I know the rule of thumb is a qt. every 100) No blue smoke while driving or on start-up and no oil leaks. Every once in awhile I get a SAI CEL during start-up or within the first mile of driving. I've checked the SAI ports and they appear to be clear (checked electronically, not visually). I'm wondering if worn valve guides allowing oil into the exhaust stream is giving the ECU false readings and setting off the SAI CEL.
Anybody have any data on oil consumption from leaking valve guides?
TIA
JC
98 C2S widebody
Anybody have any data on oil consumption from leaking valve guides?
TIA
JC
98 C2S widebody
11-13-2018, 09:13 AM
#3
RL Community Team
Rennlist Member
Rennlist Member
From my master document on servicing the 993:
"Excessive Oil Consumption - Is another reason owners consider a top-end rebuild under the assumption that the valve guides are worn to the point that excessive oil is slipping past them and burning. The logic in this seems sound. Then again I recently ran across the following comment in the 993 Rennlist Forum in reply to an oil consumption concern:
“How full do you keep the oil tank? When I kept mine at the full level I'd go through easily a qt. per 600 miles, now I keep it at min - 1/4 I use barely a qt. every 2500 miles. Even now, after spirited driving, the oil can expand to over 1/2 full.”
The implication here is that a true measure of a full oil tank is somewhat variable and overfilling may be contributing to the perception of excessive oil consumption where none may exist. Could burning the
ingested oil over-fill over time explain the clogged secondary air injector ports, potentially a self-inflicted service issue caused by simply overfilling the oil? Who knows?"
Andy
"Excessive Oil Consumption - Is another reason owners consider a top-end rebuild under the assumption that the valve guides are worn to the point that excessive oil is slipping past them and burning. The logic in this seems sound. Then again I recently ran across the following comment in the 993 Rennlist Forum in reply to an oil consumption concern:
“How full do you keep the oil tank? When I kept mine at the full level I'd go through easily a qt. per 600 miles, now I keep it at min - 1/4 I use barely a qt. every 2500 miles. Even now, after spirited driving, the oil can expand to over 1/2 full.”
The implication here is that a true measure of a full oil tank is somewhat variable and overfilling may be contributing to the perception of excessive oil consumption where none may exist. Could burning the
ingested oil over-fill over time explain the clogged secondary air injector ports, potentially a self-inflicted service issue caused by simply overfilling the oil? Who knows?"
Andy
11-13-2018, 05:57 PM
#4
From my master document on servicing the 993:
"Excessive Oil Consumption - Is another reason owners consider a top-end rebuild under the assumption that the valve guides are worn to the point that excessive oil is slipping past them and burning. The logic in this seems sound. Then again I recently ran across the following comment in the 993 Rennlist Forum in reply to an oil consumption concern:
“How full do you keep the oil tank? When I kept mine at the full level I'd go through easily a qt. per 600 miles, now I keep it at min - 1/4 I use barely a qt. every 2500 miles. Even now, after spirited driving, the oil can expand to over 1/2 full.”
The implication here is that a true measure of a full oil tank is somewhat variable and overfilling may be contributing to the perception of excessive oil consumption where none may exist. Could burning the
ingested oil over-fill over time explain the clogged secondary air injector ports, potentially a self-inflicted service issue caused by simply overfilling the oil? Who knows?"
Andy
"Excessive Oil Consumption - Is another reason owners consider a top-end rebuild under the assumption that the valve guides are worn to the point that excessive oil is slipping past them and burning. The logic in this seems sound. Then again I recently ran across the following comment in the 993 Rennlist Forum in reply to an oil consumption concern:
“How full do you keep the oil tank? When I kept mine at the full level I'd go through easily a qt. per 600 miles, now I keep it at min - 1/4 I use barely a qt. every 2500 miles. Even now, after spirited driving, the oil can expand to over 1/2 full.”
The implication here is that a true measure of a full oil tank is somewhat variable and overfilling may be contributing to the perception of excessive oil consumption where none may exist. Could burning the
ingested oil over-fill over time explain the clogged secondary air injector ports, potentially a self-inflicted service issue caused by simply overfilling the oil? Who knows?"
Andy
I wonder how many top end rebuilds have been solicited and performed under this purpousfully propagated story?
The simple fact is this, consistently over fill your engine oil, and run the distinct risk of prematurely clogged/coked SAI ports, and those who's livelyhoods depend upon high dollar top end rebuilds.
This is not to imply that worn valve guides do not promote clogged SAI ports, but rather that they are a contributing cause, along with worn rings, and overfilling the engine oil...
They say 1000 mi./quart is OK. When you get to 600-750mi./quart, you're probably due for new valve guides 
HTH
Last edited by nine9six; 11-13-2018 at 06:23 PM.
11-14-2018, 09:19 AM
#5
Burning Brakes
I can vouch for Andy's train of thought.
1995 with 117,000. When I first took ownership, it had 55K, and I kept the oil in the top 3/4 hot. One day after a really hot day of driving, revealed it was at the top of full range.
For the first few years of it's life with me, I worried about oil consumption, I seemed to add about a quart every 1500 miles.
Over the last few years I have dropped to the lower range of the stick. Not really using much oil between changes. No rebuild, or other engine work.
I do not want to go against others with engine rebuild experience, I know there are issues with worn guides. Just not in my case yet.
I do need to adjust the float level in the tank, I does not register. I trust the mechanical, eyeballs verified level more than the gauge, anyway.
1995 with 117,000. When I first took ownership, it had 55K, and I kept the oil in the top 3/4 hot. One day after a really hot day of driving, revealed it was at the top of full range.
For the first few years of it's life with me, I worried about oil consumption, I seemed to add about a quart every 1500 miles.
Over the last few years I have dropped to the lower range of the stick. Not really using much oil between changes. No rebuild, or other engine work.
I do not want to go against others with engine rebuild experience, I know there are issues with worn guides. Just not in my case yet.
I do need to adjust the float level in the tank, I does not register. I trust the mechanical, eyeballs verified level more than the gauge, anyway.
11-14-2018, 09:42 AM
#6
RL Community Team
Rennlist Member
Rennlist Member
For folks who wish to avoid over-filling measure the oil with a HOT running engine on level ground and fill the oil to the lower third of the dip stick fill range. On our cars, less is more when changing the oil as the tank and filters alone hold almost 10 quarts of oil so keeping the oil level at an incrementally lower level, I feel, is of no consequence from a lubrication perspective.
11-14-2018, 02:28 PM
#7
I’ve been keeping mine around the bottom third and my oil consumption has always been low. Do they go hand-in-hand with my car? Not sure but it’s the third 911 I’ve owned and I always keep it at half or lower on the stick.
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11-14-2018, 03:27 PM
#8
Rennlist Member
Keep mine low and experienced the same thing - no oil loss between changes yearly........first ten years I was always filling it to the high mark and always topping up.....every 500-750 miles......
