Oil Consumption '95 993
 

Hi Everyone:

I have a question about oil consumption, and I know that the issue has been discussed extensively here. However, I still can't find the answer to my specific question:

I have a '95 C4 with 58k miles. No leaks, no major issues, runs great. Yet, every 400-700 miles it burns about a quart of oil.

Is this normal? A Porsche dealership shop and an independent shop have confirmed that there are no leaks, or other issues. They say it's "normal". But is it?

Thank You in advance for your comments.

? Was this a common issue?

Had my car since 1999 and oil usage has been about the same as you describe consistently over that mileage with and without minor leaks I have tended to...

Yes, what is stated here is common.^^^

If I were you, I would warm up the car to normal operating temperatures and while on level ground, set my oil level at the low mark on the dipstick. Now drive the car for 1k miles and check it again at normal temps and level ground.

Now, note how much oil is required to bring the level to the same lower mark on the dipstick, if any.

This will tell you how much oil you're burning per thousand miles.

The low mark is used to assure no oil is being ingested into the SAI system and giving a false indicator of oil being burned through sloppy valve guides and/or ill-sealing piston rings.

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?
I change my own oil.
Here is the oil fill procedure I use today to address the whole overfill conundrum, use it at your own risk as I am not a professional automotive technician. If you have any concerns about aspects of the procedure contact a professional for their advice.

• I drive my car 5k or fewer miles a year. Once a year I purchase two five quart bottles of what is called synthetic oil in the specified viscosity, I presently use Mobil1 FS 0W-40, with its slightly higher zink formula, ordered from Wal-Mart online for store pick-up when Mobil1 is offering oil rebate coupons.
• Park the car on level ground and break-free and leave in place the passenger side rear wheel nuts slightly snugged.
• Put the rear of the car on stands, Review the P-car.com Jacking-up a 993 a DIY procedure to do this safely.
  http://p-car.com/diy/jack/
• If your car still has the under engine cover/tray remove it and store it away as some in this think it just hides oil leaks and causes the engine to retain heat. I feel it serves little purpose beyond making changing the oil more difficult. It has gone missing on most examples of a 993.
• With the passenger rear wheel now removed, I drain the oil tank and the engine case into a drain pan of at least 10 to 12 quarts in capacity. Do not attempt to drain the oil using a vacuum oil remover through the oil filler neck, it will not work and can easily damage or bend the oil level float arm in the oil tank.

The engine case drain plug is on the bottom of the engine case and points to the driver side of the car.

• I reach under the car through the passenger side rear wheel well to replace both filters. This requires removing the fender liner, the back half of the plastic rocker panel cover and detaching the heating system flapper valve housing (diverter) rubber flex duct on the passenger underside of the engine case.
  • I have used both a channel-locks or an oil filter pliers to initially break loose both the small and large filters.
  • Use a little old oil on the rubber seal on the new filter before threading it in place.
  • I make both filters as tight as I can with my bare hands and then turn the filter a quarter turn beyond this with the pliers. Although not a factory method I have never encountered a filter backing off or being unable to remove one with this method
  • I do not disconnect any steel tubes as specified in the factory procedure to drain the oil in the oil lines as my belief is that breaking the seals presents unnecessary leak failure modes and the quantity of oil present in the lines is small.
  • I do keep a can of spray electric motor/electronic parts cleaner on hand to clean off oil spilled on the engine and suspension when removing the smaller filter.
• When replacing the engine case and oil tank plugs I replace the crush rings and the "O" ring on the tank plug. On occasion, I have reused the existing metal crush rings and "O" ring with no leaks. Be sure not to overtighten the tank plug.
• Button up the plastic parts, the heating duct, mount the wheel lightly snugging the wheel nuts and put the car back on the ground
• Retorque the wheel nuts to the recommended dry thread value of 133Nm. or 96 ft/Lb in a star pattern sequence, then check the torque values by repeating the sequence on the now tightened wheel nuts.
• Refill the oil tank with 8 quarts +/- of oil and run the engine to a fully warmed state, this takes a while, not just five minutes sitting at idle, looking to the temperature and oil pressure gauges to see if they have settled into their normal operating range.
• I then, with the engine continuing to run, add additional oil, ¼ quart (8 oz.) at a time until the dip stick is at approximately 1/3 of its scale with the car on level ground with a fully warmed engine.
• If you find yourself putting ten or more quarts of oil, in total, using this procedure, you are most likely overfilling the engine. On a 993 this can have serious operating consequences and so an overfill should be addressed as soon as possible. The easiest way to address an overfill is to shut off the engine and drain the oil from the engine case as the case does not retain much oil.

I feel this method gives an additional margin of safety in avoiding inadvertently overfilling the system. If you decide to follow my measurement procedure and as a follow-up check the fill with the dash gauge and your gauge doesn’t read at about 1/3 of its range the float in the oil tank is a bit out of adjustment. Adjusting the float so the gauge approximately matches the dip stick involves draining the oil tank accessing the oil float in the tank and bending its arm a little. I have done this on my 86’ Carrera and have been told it is not too difficult on the 993. If you want to make the adjustment it is something to consider at your next oil change when the tank is drained.

• Quote:

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  Refill the oil tank with 8 quarts +/- of oil and run the engine to a fully HOT state, this takes a while, looking to the temperature and oil pressure gauges to see if they have settled into their normal operating range.

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If you run your engine, "to a full HOT state" why on Earth would one look to see if the the pressure and oil temp gauges are operating in the NORMAL range?

Wouldnt it be normal for the temp gauge to be "HOT"!

My apologies if I am experiencing a reading comprehension issue here.

I have a 1995 C2 and it uses the same amount as yours does. 85k miles FYI. I keep the oil level on the bottom 1/4 of the dipstick. I flog the hell out of it as well lol.

OP most likely you have worn valve guides and your car needs the cylinder heads rebuilt. Very very common on 993's. There are some valve guide Truthers on this site who have never rebuilt a 993 engine and insist oil consumption is because people add too much oil to their cars. I wish that was the answer but sadly it is not.

Well, could be the overfill issue stated above! Wort a try and a lot cheaper! The 0W-40 oil mentioned above are considered way too thin for an air cooled engine, but whatever floats someones boat!

If the car runns OK keep driving and wait with expensive rebuilds until the engine comunicates it's needs more directly!

This thinking has been propagated ad nauseam by those who make their living doing top end rebuilds.

Properly diagnose, then take action.

I am not saying Porsche valve guide mat'l is the most robust, but there are other more logical and reasonable factors to consider, than jumping to unvalidated conclusions!

This is precisely why the OP is receiving instruction on how to gage oil consumption, prior to making a silly, yet to be validated assumption.

Its common engineering knowledge that properly applied and executed, Root Cause and Corrective Action principles, which are data driven, uncover far more than knee jerk reactions and words spewed forth from those whose livelihoods depend upon billable hours!

NTSB investigators and engineers rely heavily upon RCCA, because airplanes fly and BIG money is involved. Unfortunately, cars dont fly and it takes a class action suit before money is spent to arrive at both root and contributing causes to a failure mode(s).

Since cars don't fly, repair shops have a heyday with repairs, real or not, before understanding or even taking the time and definitely not the money to uncover a root cause.

Not a single repair shop can produce data to validate a percentage rate of valve guide issues with regards to production numbers! Oh, and lets not forget that these vehicles are 21+ yrs in age.

Please people, lets try to put things in their proper perspective before spewing forth little pellets of unvalidated informational candy, like an uncontrolled PEZ dispenser...

Some folks interpret a warm engine as being one running at idle for five or ten minutes, generally not long enough. I use the word "hot" to add emphasis that the engine is fully warmed into its normal operating range. Your point is well taken as I will change the wording for clarity.
Andy

This is maybe a bit of hyperbole, but this is funny! :D