No? Some use an even thinner oil http://www.eurotuner.com/news/eurp_0909_mobil_1_synthetic_racing_oil/index.html The W in 5W-40 indicates the oils winter abiility, W= Winter. The 5W is measure of how thick the oil is when cold (winter) usually down to -30. The 40 accounts for how thick or thin the oil is at working temperature. Edd
] LOL Oh, and just by the by...there is no such thing as a totally 100% synthetic oil made for general car usage. They all have root stock derived from an organic compound.
Good points, well made. Its the operating temperature of the oil thats key which is why exceeding max oil temps is to avoided, however too thin an oil in a worn engine and the pump will not cope very quickly for the excess volume that passes drops the pressure. People do not realise how little pressure is needed at the crank to keep it all going for its volume, not pressure that counts as the oils secondary purpose at the crank is to remove heat (note the need for oil sprays also in some cars) and at the cams is more to lubricate although heat is generated. As for the start up benefits then I think we all need to stand back and consider what these engines managed on when running in when new. A completely different set of oil was available, primarily mineral and thicker than modern oils so I would err on the side of a thicker oil myself. Especially if the engine has a few miles on it. Modern engines are almost fully blueprinted with manufacturing tolerances manufacturers of yesteryear could only dream about and reserved for handbuild specialist engines hence they will thrive on lower viscosity oils with higher pump pressures to maintain volume and take heat away and consequently lower operating temperatures for longevity between changes. Summary, thicker wins it for me every time simply due to tolerances and wear for it promotes good pressure and volume. Gauges are notoriously inaccurate by the way unless you buy a good one with an accurate sender prefectly matched. The best are direct ie: wet fed to the gauge. Also if the gauge wasnt there and you only had a warning light then this thread wouldnt have taken place I`ll bet. Gauges create more to worry about. [
] S`wat I say anyway................................discuss...............................[]
??????????? Of course engines are built to tolerances. It is the tolerances that allow oil to pass through thereby ensuring direct contact between surfaces is avoided. Bearings and journals have agreed tolerances. Piston rings have tighter tolerances to avoid this instead relying on the oil film and smooth hardness to reduce friction.
??????????????????????? In which case the pressure reading would be a negative! There is no aspect of the engine that would create a negative (suction) pressure. Without head (positive) pressure the oil wouldn't travel anywhere. The only negative pressure in an engine is gravity. The forces upon a journal or bearing squish the oil out, without positive pressure it cannot be replenished.
Nothing wrong with a 10w/30 in the correct or suitable applications. Just not on our Flat Tappet designed motors from the 80's. Funny how we were reading about a lot of advanced engine wear in UK 944s and 911s in British magazines a few years ago. Guess they must have all been using VR1 20w/50 and the thicker oil created a lot of premature engine wear.
]. I agree I think a few ppl have made the mistake of running oils like the old 0w Mobil 1. The thing ppl don't understand about driving in the UK is that our climate is more or less irrelevant. If you live in or near one of the cities the car could be spending much of its life sat in traffic jams. I drove almost 3 hours in London traffic Friday last and the result was my car broke down from a heat related illness (burned plug lead for starters, may have overheated autobox). In these circumstances where the fan is constantly on/off for hours at end I bet the heat build up under the bonnet is far higher then blasting across the outback, AND with a decent amount of rpm on the motor at least the oil pressure is reasonable rather then spending hours bobbing around 2 or 3 bar. My dad drove busses for many years and he tells me they often had breakdowns caused by the transmission overheating in traffic. If you guys recall the reason I originally switched to Mobil 15w-50 was because I spent a lot of time in traffic (south coast + summer = traffic nightmare) and I was loosing to much oil on 10w-40 oil, switched to 15w-50 and the loss more or less went to 0. OK this is on a 150+K miles motor but then most of our cars are high mileage motors now.
I think the key phrase in Marks post is 'Driven Hard'. When driven hard oil temps increase, viscosities decrease therefore the oil will thin. On 5w40 my old 944 hardly used a drop of oil for normal street driving - it would go between oil changes without needing a top up and use about half the distance between max and min on the dipstick. But on trackdays i'd be topping the oil up after every session on track (about 15 mins). Clearly if I was heavily tracking the car a higher grade of oil would be prudent. In anycase 15w50 is still within the Porsche recommended range.
. I know in a 944 engine it doesn't help in the slightest. Although to be fair when my old engine had 0W40 in it (previous owner thought the engine had a stuck tappet) it did hold the oil pressure at 2.5bar when warm (driven for quite a while) and 5ish when on the run but as said gauges are not the most accurate of things in the world. It did however start to pee oil out of the crank seal not many months after it was put in, in addition to the lingering smell of oil. It's not about what's the thinnest but moreso about what is suited to the job in hand. In the case of some forum members here, they are from France and Australia, two relatively different climates when compared to the UK. Tolerances have more to do with things than people appreciate. In some of the rebuilt BL engines I've seen they seem to appreciate running more on a 20W50 than they do on a 15W40 (where the oil pressure gets lower than spec in even an Ivor Searle rebuilt engine with next to no miles). The Porsche is no different IMO (although I understand the pistons to bore tolerances are closer than people than people think). FWIW, I ran my last engine on 15W40 semi (it was on its last legs though) and my current one is on 10W40. I'm toying with going to 15W50 if I take up track days though.Tony, why are you getting cylinder wash on the track? What a lot of people are missing (and this is from heavy traffic driving to track work) is that the oil is there not only to provide a lubricant and act as a coolant, but also to actually help prevent those expensive metal engine internals from colliding and destroying each other. As most of you would know the tolerances we are dealing with are sometimes % of fractions. Quite simply, having a higher weight oil that doesn't break down and get too thin under heat is offering greater protection than some of these very light weight oils that are being bandied about. Remember that the Porsche owner's manual right up to some 996's were recommending a 20w/50 mineral based oil amongst others. Sure some of the others would have been lighter weight 'synthetic' marketed oils but they are still given the option. Also we recognise that these oils won't give quite as good fuel economy as others, but again, that's something most Porsche owners wouldn't have at the top of their list of priorities.
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