Oil Consumption

I have the same issue with my C4S. My oil consumption has been tad high recently but it does seem to be a common nature for these M96/97 engines.

I run Mobil Super 3000 5W40, thinking to change to Millers ND 10W50.
However, I was cleaning my TB and noticed fresh oil in the Plenum... possibly my AOS is begging to fail. Not getting any smoke, high vacuum pressure, or loss in power etc. I do have a little squeak, again I have heard this could be AOS related. Note, I have replaced my belt and idler/tensioner bearings.

With regards to RMS/IMS sweat, I wouldn't worry about it, unless its dripping at an alarming rate on your garage floor

Yas.SYC4S said:

I have the same issue with my C4S. My oil consumption has been tad high recently but it does seem to be a common nature for these M96/97 engines.

I run Mobil Super 3000 5W40, thinking to change to Millers ND 10W50.
However, I was cleaning my TB and noticed fresh oil in the Plenum... possibly my AOS is begging to fail. Not getting any smoke, high vacuum pressure, or loss in power etc. I do have a little squeak, again I have heard this could be AOS related. Note, I have replaced my belt and idler/tensioner bearings.

With regards to RMS/IMS sweat, I wouldn't worry about it, unless its dripping at an alarming rate on your garage floor

Click to expand...

You do get oil there but for an aos then it would be a fair amount , you would also get more smoke as obviously that oil is going to get burnt .

Off hand it doesnt sound like an aos .

Noise is a vacum noise so a whistle / screech is more how i would describe it .

Might just be drive belt slipping .. when wet perchance ?

Ive also read here that different oils tend to use more / less .

I would always say " customer to monitor " see if it gets worse before shelling out any hard earned cash

Yas.SYC4S said:

I have the same issue with my C4S. My oil consumption has been tad high recently but it does seem to be a common nature for these M96/97 engines.

I run Mobil Super 3000 5W40, thinking to change to Millers ND 10W50.
However, I was cleaning my TB and noticed fresh oil in the Plenum... possibly my AOS is begging to fail. Not getting any smoke, high vacuum pressure, or loss in power etc. I do have a little squeak, again I have heard this could be AOS related. Note, I have replaced my belt and idler/tensioner bearings.

With regards to RMS/IMS sweat, I wouldn't worry about it, unless its dripping at an alarming rate on your garage floor

Click to expand...

Hi Yas :thumb:
I was also intending on switching to Millers in January when I drop the oil and similarly currently running on Mobil Super 3000 5W40 as well.
Heard mixed views regarding oil type/viscosity etc.
87,800 miles covered..

Thanks Demort,
I did find fresh oil in the intake, I wouldn't say a large quantity. I cleaned the intake and TB, something I will monitor and check again after a few miles. The car does not smoke, so the oil has to be going somewhere?? no visible leaks, performance is brilliant (keeping up with a 996 GT3 on B roads last weekend) :dont know:
Regarding the squeak, its not as frequent since changing my belt/rollers but seems to appear when warm, stationary (I did check all other pulleys for play).

C4-Storm - I think switching to Millers is a good option and most have done the same. I think Mobil 3000 is not suited for our cars in particular. I only drive my car in good weather, SORN for the winter months. So switching to 10W50 is a safe option with regards to protection from winter 'cold starts'.
Do you have any concerns with heavier weight oil?

Yas.SYC4S said:

Thanks Demort,
I did find fresh oil in the intake, I wouldn't say a large quantity. I cleaned the intake and TB, something I will monitor and check again after a few miles. The car does not smoke, so the oil has to be going somewhere?? no visible leaks, performance is brilliant (keeping up with a 996 GT3 on B roads last weekend) :dont know:
Regarding the squeak, its not as frequent since changing my belt/rollers but seems to appear when warm, stationary (I did check all other pulleys for play).

C4-Storm - I think switching to Millers is a good option and most have done the same. I think Mobil 3000 is not suited for our cars in particular. I only drive my car in good weather, SORN for the winter months. So switching to 10W50 is a safe option with regards to protection from winter 'cold starts'.
Do you have any concerns with heavier weight oil?

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Hi mate.

I don't think so. From what I have heard the benefits outweigh any concerns however I am definitely no expert and have just relied on info from others really. My only other consideration is that all seems okay and car is running pretty nicely (my oil consumption query is being monitored!). The fella I bought mine from has had 5 of them and said don't mess with it, he also said he doesn't do forums! On balance I think I will switch as a preventative measure, taking the advice of some of the guys on here.

What's your view on this Demort?

:thumb:

@ Yas.SYC4S

You do get oil in the intake mainifold as standard , i remember being suprised by that some 13 years ago when i started on these cars .. its also difficult as with an aos failure or just on its way out you also get oil in the mainifold .

To give you an idea , i Worked on a Boxster , it had a bit of excess smoke but not what i would call huge , had the throttle body off and there were small puddles of oil in the mainifold to the point i could almost dip my fingers in it .. this was indeed the beginnings of the AOS on its way to heaven but no real symptoms .

When an AOS HAS gone then you can almost scoop out the oil , same as with heavy bore score im afraid ( i probably shouldn,t have mentioned that ).

Hence all i can say without looking is customer to monitor but i expect you just have the normal amount which does indeed get burnt in the cyls .

Just to be akward though , if a 996 has its original AOS still fitted then it might be worth thinking about changing it .. along with Cam tensioners .. 2 things i have changed my mind on since being at an indy and that gos against my normal " if it aint broke dont fix it " comments .

@ C4-STORM

I dont get involved on the oil type discussions ( safest for me ) , you lot have experience of it .. i fit either Mobil 1 0/40 or 5/40 if its done a few miles .

At OPC then all i used was Mobil 1 0/40 on every applicable car .

From reading here then different types or grades of oil seem to use different amounts on the same car .. if i serviced your car then i would use Mobil 1 5w/40 .

Hartech recomend different types so i bow to their judgement .

Demort said:

@ Yas.SYC4S

You do get oil in the intake mainifold as standard , i remember being suprised by that some 13 years ago when i started on these cars .. its also difficult as with an aos failure or just on its way out you also get oil in the mainifold .

To give you an idea , i Worked on a Boxster , it had a bit of excess smoke but not what i would call huge , had the throttle body off and there were small puddles of oil in the mainifold to the point i could almost dip my fingers in it .. this was indeed the beginnings of the AOS on its way to heaven but no real symptoms .

When an AOS HAS gone then you can almost scoop out the oil , same as with heavy bore score im afraid ( i probably shouldn,t have mentioned that ).

Hence all i can say without looking is customer to monitor but i expect you just have the normal amount which does indeed get burnt in the cyls .

Just to be akward though , if a 996 has its original AOS still fitted then it might be worth thinking about changing it .. along with Cam tensioners .. 2 things i have changed my mind on since being at an indy and that gos against my normal " if it aint broke dont fix it " comments .

@ C4-STORM

I dont get involved on the oil type discussions ( safest for me ) , you lot have experience of it .. i fit either Mobil 1 0/40 or 5/40 if its done a few miles .

At OPC then all i used was Mobil 1 0/40 on every applicable car .

From reading here then different types or grades of oil seem to use different amounts on the same car .. if i serviced your car then i would use Mobil 1 5w/40 .

Hartech recomend different types so i bow to their judgement .

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Okay mate, I appreciate your comments :thumb:

Thanks for your comments Demort.
From what you said, I believe the oil residue in my intake seems to be the 'norm' I did not have puddles, just wetness of fresh oil in and around the plenum.

I will change my oil to Millers (service due after winter) and monitor the consumption.
I wonder if any change in consumption from Mobil 3000 5W40 to Millers ND 5W40/10W50?? Anyone had any experiences?

Any areas that could leak under pressure?

Yas.SYC4S said:

Thanks for your comments Demort.
From what you said, I believe the oil residue in my intake seems to be the 'norm' I did not have puddles, just wetness of fresh oil in and around the plenum.

I will change my oil to Millers (service due after winter) and monitor the consumption.
I wonder if any change in consumption from Mobil 3000 5W40 to Millers ND 5W40/10W50?? Anyone had any experiences?

Any areas that could leak under pressure?

Click to expand...

Been recommended the NT 10W50 but not sure if there is a definitive on this TBH

Yes, everyone does point towards 10W50 with regards to Millers NT oil. I just saw they do a 5W40 version, wanted to know if anyone uses it, and if they noted any change in consumption from Mobil oils.

mine is a 2001 C2 Tiptronic with 33k. ive covered 11k in the past 16 months and have used 3.5 litres of oil to top up. It also had a service at Porsche main dealer in March this year. no leaks.

It's a complex subject.

Piston ring sealing is influenced by several factors but most of the sealing is as a result of the pressure above the piston feeding into the ring grooves and pushing out on the piston rings from inside - the sealing pressure therefore varying with revs and throttle opening. There are also some rings that are slightly tapered and tilt in the grooved location in the piston and wipe oil away from the bore on the downstroke.

This means that the amount of throttle opening (or torque developed) influences the sealing pressure between the ring and cylinder wall. You can accelerate just as quickly sometimes on say three quarters throttle as full throttle but is makes a difference to the breathing and pressures sealing the rings - and some people rarely use aggressive throttle openings but as a result experience less sealing.

Rings designed to tilt can tilt too much if the bores are worn and change from being a better solution to a worse one. Worn bores can resulting the piston pumping oil upwards as the piston rocks over TDC to be burnt on the next cycle.

Changing down in manuals also makes a difference because those who select a lower gear and use a lot of engine braking create the maximum upper cylinder vacuum and this can lift more oil to pass the rings (or the valve seals) and can wear the critical ring groove gap circumferentially between the piston and ring and this in turn influences sealing.

If the rings are leaking due to excessive bore clearances then the increased crankcase pressure can force too much oil mist into the breather system and result in some reaching the upper intake area and being re-burnt (increasing consumption).

There are different ring designs (some protected by patents) used by different ring manufacturers (some more expensive than others) and some engines (including Porsche) have been manufactured with different versions between models and builds. Some might suit the particular owners driving styles and oil choices better than others but not a different owners - making it impossible to isolate advice without delving into factors beyond any designers control.

On top of that the Lokasil standard cylinders distort oval as the years go by and increase the piston clearances (largely I think governed by casting variations and differences in the distribution of silicon particles in the Lokasil preforms).

Then previous owners will have driven cars differently - all influencing the wear pattern of rings - some of which can rotate (not being pegged) so moving the ring gap (which gets bigger as bores wear or go oval) and if it ends up at the bottom of the bores allows some oil to drip into the upper cylinder on cooling down to result in smoke on the next start-up.

The type of oil used, average coolant running temperatures (hence bore expansion and piston sizes and the piston shape that varies with running performance), driving styles, etc - all influence how the engine wears internally so by the time most of these cars are on the third or fourth owner it is impossible to asses the influences of these variables over their life.

However having explained some of the many influences on oil consumption that can result in one perfectly reliable car exhibiting more consumption than other perfectly reliable cars - as long as the engines perform OK - what is the problem splitting hairs between the cost of an occasional top up in the overall running costs of the cars/1000 miles - really insignificant.

When it comes to bore finishes, the amount and distribution of silicon particles (in Lokasil - which varies) or the angles and depth of honing grooves (in Iron or Nikasil) also influence the resulting oil consumption - however - too little oil consumption can mean that rings and bores are wearing out quicker and can eventually lead to problems before other engines with modest oil consumption do - because the very minute oil slipping past the oil control rings can - in turn - protect the ring wear by providing better upper cylinder lubrication.

As long as the consumption is reasonable (within Porsche's recommendations) and there are no other signs of an engine problem (no deep scoring etc) there is little to worry about even if your own car uses a little more than someone else's.

Many high performance engines are designed to accept a minor oil consumption to protect the cylinder ring to bore surfaces and perform better. Personally - as long as the engine is running OK - I would prefer a modest oil consumption to none at all (with my own style of driving (which is not slow) but for others a different scenario may be preferable.

The AOS will eventually start leaking and with bore scoring there is of course grooves for oil to slip past to the upper cylinder.

However - I think the variables are too many to make too much of minor differences between owners cars and that most of the debate for most owners is possibly creating unnecessary concern.

Baz

Thanks for the finer detail Baz.

"However having explained some of the many influences on oil consumption that can result in one perfectly reliable car exhibiting more consumption than other perfectly reliable cars - as long as the engines perform OK - what is the problem splitting hairs between the cost of an occasional top up in the overall running costs of the cars/1000 miles - really insignificant."

I totally agree with the above - the cost of topping up or even replacing the engine oil when due is not an issue. In fact I would rather change the oil more regularly/opting for a better quality product in order to maintain the engines components as much as possible.

That technical detail fully explains the variables from 1 car to another and certainly for me makes perfect sense :thumb: