Oil

Richard Dawson · Apr 16, 2005

I am new to this forum and have just read the technical stuff which I found interesting. I am about to upgrade my 94 C2 suspension but not with a view to track work and so am looking for inspiration.

I note the oil recommended is all 0W or 5W. I am not disputing this advice, especially for Uk based road driving but have found that such thin oil can lead to lower oil pressures at sustained higher engine speeds. My last Porsche was a 964RS in which TECH9 were keen to use Mobil 1 Racing which is 15W 40.

In a BMW M5 and an Alpina B10 Biturbo I have had before I found thin oils led to issues.

Given the fact the 993 engine is an old design I am not wholly convinced its internal tolerances even in the hydraulic lifters mean 0W is necessary (as in say a Mondeo) or particularly good especially if trackdays are a regular feature.

Does anyone have any experiences on this issue?

Kind regards

oilman · Apr 18, 2005

Richard,

You can still use a 5w-40 even on a track car but you'll need to ensure that it's a quality one. The grade is perfectly capable of standing up to track work so long as it's a proper synthetic (pao/ester) basestock to ensure that the oil is shear stable.

Unless you're running obscene oil temperature of around 150 degC then I would recommend using a "race" 5w-40 like Silkolene PRO S or Motul 300V. If you are experiencing higher temps then a step up to a 10w-50 may be necessary.

Hope this helps

Cheers
Simon

oilman · Jan 16, 2006

I actually suggested Silkolene PRO S 5w-40.

http://www.opieoils.co.uk/performance_lubricants/pdf/silkolene/PRO%20S%205w-40%20and%2010w-50.pdf

I would guess the one you are using will be a blend of different basestocks, group III & IV most likely.

Cheers
Simon

sawood12 · Jan 16, 2006

I've got Silkolene Pro 5W40 (which is an ester oil) in my 110k miler 944 and it fine. No leaks or increased usage at all. I don't believe all this 'loose engine' stuff. In any case there is no difference between 5W40 and 15W40 once the car is upto temp.

I can't think of one good reason not to get an Ester oil. The extra start-up protection the Ester oils give makes it a no-brainer.

oilman · Jan 16, 2006

Does this help?

Basestock categories and descriptions[/b]
[/b]
All oils are comprised of basestocks and additives. Basestocks make up the majority of the finished product and represent between 75-95%.

Not all basestocks are derived from petroleum, in fact the better quality ones are synthetics made in laboratories by chemists specifically designed for the application for which they are intended.

Basestocks are classified in 5 Groups as follows:

Group I

These are derived from petroleum and are the least refined. These are used in a small amount of automotive oils where the applications are not demanding.

Group II

These are derived from petroleum and are mainly used in mineral automotive oils. Their performance is acceptable with regards to wear, thermal stability and oxidation stability but not so good at lower temperatures.

Group III

These are derived from petroleum but are the most refined of the mineral oil basestocks. They are not chemically engineered like synthetics but offer the highest level of performance of all the petroleum basestocks. They are also known as "hydrocracked" or "molecularly modified" basestocks.
They are usually labelled/marketed as synthetic or semi-synthetic oils and make up a very high percentage of the oils retailed today.

Group IV

These are polyalphaolefins known as PAO and are chemically manufactured rather than being dug out of the ground. These basestocks have excellent stability in both hot and cold temperatures and give superior protection due to their uniform molecules.

Group V

These special basestocks are also chemically engineered but are not PAO.
The main types used in automotive oils are diesters and polyolesters. Like the group IV basestocks they have uniform molecules and give superior performance and protection over petroleum basestocks. These special stocks are used in all aviation engines due to their stability and durability. Esters are also polar (electro statically attracted to metal surfaces) which has great benefits. They are usually blended with Group IV stocks rather than being used exclusively.

It is common practice for oil companies to blend different basestocks to achieve a certain specification, performance or cost. The blending of group IV and V produces lubricants with the best overall performance which cannot be matched by any of the petroleum basestock groups.

Cheers
Simon

KEVIN993S · Jan 22, 2006

Apologies for being a pain and raising the dreaded question again .....

I've read the tech article and all the "recent "posts on the right oil for 993 but to be honest I'm still a wee bit confused as to what to buy... I would normally use what Porsche recommends and go for Mobil1 0-40W but ....previously OPC advised that on older engines (968Sport at the time) 0-40 was too thin and I should buy the Mobil1 Motorsport 15-40W (or 50 cannot quite remember) which is a wee bit thicker at cold and therefore reduces leaks.

You pays your money and takes your chances I know but I would rather be sure I was not doing anything too silly....

- thoughts ???

BTW the car has 56K miles

Cheers,
Kevin

oilman · Jan 22, 2006

Kevin,

You Porsche at 56k is still a low mileage.... no need for a thicker oil then what is recomended, go for a good 0w-40/5w-40 full synthetic.

Cheers

Simon.

KEVIN993S · Jan 22, 2006

Thanks ... Mobil1 0-40W it is !!

Cheers
Kevin

cobalt911 · Oct 19, 2009

Well, if over-filled then it can be a problem!

The best way to know is to find a flat place, keep car running until it is REALLY warm (over 20 minutes from cold minimum is my experience) leave the engine running (do not wear a tie, lots of spinning parts in the back ha ha) and then check the dipstick. While idling for a few minutes the oil level meter in the car should sit about 2/3 up the scale (I never fill to the top of that marker) and the dipstick should be self-explanatory. I think many folks have dodgy oil level gauges in the car so the dipstick on a warm, running engine (that has been at idle for a few mins) is the gold standard...

So - if worried over-full run the procedure above and if over the dipstick markers then you need to lose some!

Good luck...

Mark

Gordon Attar · Oct 19, 2009

As Cobalt911 said checking the dipstick whilst the car is hot and idling on a flat surface is the only way to be certain.

Likewise no more than 2/3rds on the dashboard gauge, and likewise on the dipstick, remember oil will expand when very hot and 911's run a lot hotter than those water cooled thingy's.

Mark Elder · Oct 19, 2009

Similarly - I don't go to the top of the gauge on the dash. I've learnt that 100% on gauge = slight overfill on stick.
On the other hand I do run the gauge right down to the red because top of red = half way between "min" and "max" on stick.

Don't even think about checking either gauge or stick until oil thermostat has opened (temp gauge has risen to 8o'clock mark and then dropped for first time)

Porker993 · Oct 20, 2009

Yes, my dash guage is pretty accurate, and gives a pretty good indication of where the oil level is on the dipstick. This is something I have learnt to trust over time.

Knowing how the sender in the tank works, (I've seen one removed), I figure if the engine is hot and the stat has opened, and the oil level guage is showing slight wobbly movement, it must be working ok.