Porsche Enthusiasts Club Forum

What oil is best for a 1990 S4? It has 70k miles and no leaks that I am aware of.

Porsche use Mobile 1 0/40. Since owning my 1987 s4 all i use is Quantum Platinum from T.P.S Trade Parts Services it is a fully synthetic 5/40 trade price £20 inc vat 5 ltr.

Hi

I use 15/50 full synthetic from OILMAN.. >>> http://www.opieoils.co.uk/p-68899-fuchs ... e-oil.aspx

Club members get a discount, I am sure Sean will tell you the code....

0/40 is too thin for an S4 IN MY OPINION...

All the best Brett

In my opinion 15/50 is a to thicker viscosity for start up 50 great for long fast hard running .E.G a10/30 and a 10/40 oil have the same viscosity when cold blow 0c when hot at 100c the oil with the number 30 is thinner than the oil with number 40. This is all across the board with all oils.

Too late just bought some mobil 1. I'll give it a try and if I get any problems I will try something different.

Hi

You will be able to tell easily...get someone to drive behind you and accelerate HARD (with the engine hot)... they will see a lot of oil smoke...depending on how worn your engine is.....

You will probably see it in your rearview mirror as well

You will also start USING oil at an alarming rate.....so keep an eye on the dipstick...

All the best Brett

Does not matter what oil you put in if its a tired engine it will smoke . With regards to my use of Quantum Platinum oil T.P.S. part number SZGB115QLB00511 5/40 fully synthetic £20 5/ltr. Done 20k in s4 over 4years/ all so run Audi a8 on same oil 30k and last of all my lads Smart car roadster as done a total of 140k the last 110k on the same oil. IF its good enough for VW SEAT SKODA AUDI & COMMERCIAL VW TO USE AND SELL ITS GOOD ENOUGH FOR ME cheers.

Hi

Just checked Qunatums site... even they recommend a 10/40 (synta) for an S4.... not a 5/40

Very cheap though for a full synthetic...

All the best Brett

UK Porsche main dealers used to use Mobil-1 Motorsport 15w50 in all cars of this era through to about 7 years ago when they decided to rationalise the oil held at dealerships.

As they were seeing mostly 996 and Boxsters, and were about to be seeing 987's and caymans, they decided to reclassify all Porsche models to be approved to use 0w40 and 5w40 so they didnt have to stock more than one oil at the main dealers.

The result was a lot of 993's which leak and smoke.

Because not many dealers see many 928's, I have not seen many of them coming in after a main dealer service smoking.

Typically I would expect to see 928 S4's consuming more oil when running on 0w40 or 5w40 compared to a 15w50.

If its a cat equipped one you might not see the smoke, as the cat will convert it into heat and water vapour (or at least try), until the car returns to idle from a hard run and the cat has a chance to cool.

Mobil have stopped production of Mobil 1 15w50, which is a real shame, loved that oil and not sure about its replacement yet.

I doubt lasting damage will occur from using a 5w40 oil, as the film strength will be the same between that an a good 15w50, apart from maybe additional carbon build up on piston rings and valve stems.

Its true a newish 928 engine may tolerate 5w40 more than a worn one, but a worn engine isnt a dead engine, and a 5w40 oil may cause a less worn engine burn oil which otherwise might not.

However, a 5w40 or 0w40 oil will release a little more power from and engine as there will be slightly less drag within the engine.

Hi 10/40 Quantun Synta is a semi synthetic .You will get more carbon build up using semi synthetic over fully synthetic.Cat equipped cars will not convert all used oil in heat and water vapour there would be oil in exhaust tail pipe and high emissions for M.O.T. So other Porsche cars do not do high mileage? engines that leak any fluid its from a worn seal or damage gasket not because of fluids.

Read again. I did not say it would "Will convert all used oil in heat and water"

I said
"If its a cat equipped one you might not see the smoke, as the cat will convert it into heat and water vapour (or at least try), until the car returns to idle from a hard run and the cat has a chance to cool.

The oil is a hydrocarbon, which the thermal and chemical reaction in the catalytic converter will attempt to convert into heat and water vapour.

How much work the catalytic has to do in conversion of this hydrocarbon into heat and water vapour (and carbon dioxide) will depend on the quantity of oil being consumed.

Typically, as per my case example, will in a fit 993, cause smoke at idle (when the cat is cooling) but will not cause smoke off idle when the cat is within its thermal efficiency range.

Typically, if you throw a massive amount of oil through a exhaust a cat is never going to combust that oil, however the difference between a lower viscosity oil and a higher one will be additional oil being consumed in a level that all else being good, will still pass an MOT test.

The other problem is that the catalytic converter is designed to convert X amount of hydrocarbons on average per unit of time, which will account for a worn engine, however the additional hydrocarbons and a worn engine along with a low viscosity oil will cause an excessive amount of heat within the catalytic converter, which can cause it to go into meltdown, possibly causing fire and a plugged cat. Unlikely, but possible.

If an engine is heavily worn, it may burn any oil of course, but put a 0w40 or 5w40 into that engine and it will burn more oil than when it is filled with the original recommended 15w40 oil. The big difference is that the Porsche tolerance of oil consumption with what is and is not acceptable is for example (on some models) 1 litre in 1000km.. An engine running on 15w50 may consume just under that limit, where as an engine running 5w40 may consume more than that limit. To the layman, this will decide an engine rebuild when not strictly necessary.

Carbon and a semi synthetic, well this is true, but we tend to find 928 engines do not have a problem with carbon, sludge or varnish on Semi synthetics, we have seen a problem with magnatech oil on all porsche engines causing this.

Turbo charged engines tend to carbon up the turbo centre sections on semi synthetics, but that is mainly due to low pressure combined with high heat, along with foaming caused by the central shaft spinning at 100,000 plus rpm, but on the engine side, I have not seen problems. Probably because the engines were designed to run on it. Later engines have higher engine temperatures (both combustion, egt and core temps) which can cause carbonisation of the engine oil, but fortunately the 928 runs cooler than this.

You can of course run what you like in your engine, there was even a study performed by Mobil in Germany where they ran a HGV on rapeseed oil as fuel and crankcase oil that made for interesting reading, but I am not about to advise its use.

In much colder climates Porsche specified you could go down a 5w40, but we are talking much colder than the UK gets on average.

My advice stands. I don't want to seem argumentative, if I see some advice I would not agree with, I have to give my opinion, if then I get questioned on that opinion I need to justify that opinion, I will try to keep to the facts, I do not intend on upsetting anyone and I do genuinely want to encourage members to exchange advice. So if you see me not agreeing, do not take it to heart or get offended, or even turn it into a "last word" competition.

You like a lower viscosity oil than I, thats great, lets talk about the benefits of each oil, I have stated why I think 15w50 will be a better choice, lets now talk about what benefits you think are felt with a 928 running 0w40 or 5w40

A "which oil" thread.......





and nobody has mentioned ZDDP yet

I typed out a reply twice, and never posted it. Is the ZDDP really that critical for your thrust bearing?

Critical for cams & high pressure bits.

Ahhh.. ZDDP

Zinc Dithiophosphate, excellent stuff, slowly kills catalytic converters, but essential as a wear inhibitor in engines designed before circa 1998, especially in areas of high pressure or high oil sheer with oil at low pressure.

Problem is, engine manufacturers have been making engines so they need this stuff less, so that oil companies can use less, so that the catalytic converters will last longer. Unfortunately, this means owners of classic Porsche, who want a high performance oil, but with plenty of ZDDP in it, are running out of options.

Mobil 1 Motorsport 15w50 has 1200 parts per million ZDDP, its replacement, Mobil 1 Extended Life would on the surface seem to have 1300 ppm of ZDDP, but to be honest, they way they are quoting it, seems slightly missleading, as they are quoting phosphate content rather than zinc dithio-phosphate, so I am waiting to hear the official line from mobil before I can recommend that oil

The other alternative is turbo diesel oils, which it seems have high levels of ZDDP, as ZDDP does not hurt diesel particulate filters, and diesel engines have plenty of high pressure and high sheer issues in the low pressure oiling of the engine. They also normally have a good detergent package, but how do I tell a customer I recommend a diesel oil for their engine?

As I said once before... its a field of claymoors