Engine Oil - 2.7 - what do you use
- Thread starter AntB
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Neil Haughey
New member
The owners manual for the S2/turbo and 968 both say you can go up to 20-50, so if you use a 20w-50 oil you are within Porsche specs. I had a book written about the development of the Saab 9-5 back in the mid 90's. It was pretty clear about the trend there in Saab/GM and by extension across the industry to slim down every component to minimal weight and much tighter tolerances. The whole point of the exercise in tandem with thin when cold oils was/is to improve fuel economy.
Still though if one is loosing oil when hot with a 5w-40 oil I can't see how moving to a 10w or 15w 40 oil will make any difference.
Still though if one is loosing oil when hot with a 5w-40 oil I can't see how moving to a 10w or 15w 40 oil will make any difference.
944 man
Active member
I have to disagree with Scott's post. 5W & 10W oils will probably be the cause of excessive consumption in atmospheric engines: a position taken by a number of well-regarded independants. I dont have access to Scott's manual of course, but both the series one and the series two & Turbo manuals that I have access to both state that from -10c to 40c+, Porsche suggest using 20W-50 multigrade oil. Later recommendations may differ, but not for normally aspirated cars, as far as I recall...
Simon
eta: beaten to it by Neil: I took far too long checking... [
]
Simon
eta: beaten to it by Neil: I took far too long checking... [
]Exactly.
Cold start and cold load are when the motors get worn the most. Having a thin light w version won't leave much residual oil up in the camshaft / tappet region. Especially if the car has been sitting for a while. Interestingly Mobil have re introduced ZDDP content into some of their performance oils. Perhaps they've been reading some forums?
Neil Haughey
New member
I have heard it before many times that engines from the 80's often don't get on with modern synthetic oils. I can remember back with my old 900 it was often said that the synthetic oils reacted with the material they used back then for the engine seals. I was never sure but I did know of several ppl that had engines that started leaking like a sieve as soon as they switched to synthetic oil, even if the synthetic had the same grade. Still though this doesn't explain the observation you get Simon but could in theory explain why sometimes ppl get a lot of oil loss with Synthetics.
sawood12
New member
OK, so i'm potentially not getting enough lubrication to my cylinder head? How is using a thick oil going to improve that situation? Surely it is easier for an engine to suck up a thick oil than it is a thin oil? I certainly find it easier to suck water up through a straw than A Mcdonalds triple thick milkshake. The whole point about cold start protection is that thin oil flows easier and better than thick oil. That's the whole reason why multigrade oils were invented. And protection of engine parts is all about oil flow - if your oil doesn't flow you're not protected. So when you start the enigne from cold a thin oil will flow round the enigne more quickly, protect moving parts better and much earlier and continue to protect until such time the oil warms and settles down to warm running viscosity.
I simply don't understand how a thicker oil is going to improve cold start protection and running - it goes against logic, common sense and all advice and recommendations i've ever had from anyone in the know, Porsche specialists included. I'd love for someone to explain this in engineering terms.
Also alot of the myths and folklore about synthetic oils originated from their early days when they were still being developed and probably did have some problems. Modern synthetic oils are a different prospect altogether. In fact is there has probably been more technological developments and advances in motor oils over the last 20yrs than any other aspect of the car.
Anyway we can argue about the logic, but the manual is the manual and it seems I may have misread it!!![] Just looking at my Owners Hanbook as I type against recommended multigrade oils. Seems like the 5w rating is just outside actually, which surprises me as i'm sure I referred to the handbook when choosing my grade of oil. For multigrade oils and climatic temps the manual recommends :-
-30 - 0 = 5w30
-15 - +20 = 10w30
-20 - +35 = 10w40/10w50
-15 - +40 and over = 15w40/15w50
-10 - +40 and over = 20w50
Looks like 10w40 next time for me. But i'm convinced a modern 5w40 gives better cold start protection than a 20yr old 10w40.
I simply don't understand how a thicker oil is going to improve cold start protection and running - it goes against logic, common sense and all advice and recommendations i've ever had from anyone in the know, Porsche specialists included. I'd love for someone to explain this in engineering terms.
Also alot of the myths and folklore about synthetic oils originated from their early days when they were still being developed and probably did have some problems. Modern synthetic oils are a different prospect altogether. In fact is there has probably been more technological developments and advances in motor oils over the last 20yrs than any other aspect of the car.
Anyway we can argue about the logic, but the manual is the manual and it seems I may have misread it!!![
] Just looking at my Owners Hanbook as I type against recommended multigrade oils. Seems like the 5w rating is just outside actually, which surprises me as i'm sure I referred to the handbook when choosing my grade of oil. For multigrade oils and climatic temps the manual recommends :--30 - 0 = 5w30
-15 - +20 = 10w30
-20 - +35 = 10w40/10w50
-15 - +40 and over = 15w40/15w50
-10 - +40 and over = 20w50
Looks like 10w40 next time for me. But i'm convinced a modern 5w40 gives better cold start protection than a 20yr old 10w40.
Neil Haughey
New member
ISTR the problem with top end wear is allegedly due to the thin oils running out of the head when the car is sat, hence when started up, the engine for a few seconds has very little or no oil on the camshafts etc. I have no idea how true this is but there does seem to be anecdotal evidence that cars run with thicker oils have shown much less top end wear. ISTR an Australian 928 specialist had some stuff about this on his website.
I spent a bit of time researching what the oil rating means and I will share it for the benefit of anyone that might not know it. Im sure you will let me know if I have it wrong .
A fully/semi synthetic oil has additives in it that reduce the decrease in the viscosity of an oil as its temperature increases, it still gets thinner just not as much as it would. The reason to do this is so you can have a thin oil at low temperature for cold starts and not end up with a really thin oil at high temperatures that leaks all over the place. This is where the kind of rating 4w40 comes from and it means that at low temperatures (ambient?) the oil will have a viscosity of a grade 4 oil and at high temperatures (running temp?) the oil will have the viscosity of a grade 40 oil. Remember the number does not denote the actual viscosity it only tells you what grade of oil the synthetic oil is behaving like at the given temperature. For example a synthetic oil could actually have the same viscosity at low and high temperatures. Essentially it means the effective grade of the oil changes with temperature so its like having multiple grades of oil within one oil and picking the grade you want for a given temperatre to give you the viscosity you need. Its very clever stuff.
Another thing to note is that the charachteristics of an oil go beyond viscosity. For example if you take a fully synthetic oil and a synthetic oil of the same viscosity a fully synthetic oil will have a greater tendency to leak through gaps due the synthetic oil having a greater surface tension (im not sure exactly what you call it). For example this is what causes water to form globules rather than spread completely flat, on your windscreen for example, whereas oil tends to flow out flat. I think a synthetic oil has a greater surface tension than fully synthetic oil and thus should help stop leaks.
. A fully/semi synthetic oil has additives in it that reduce the decrease in the viscosity of an oil as its temperature increases, it still gets thinner just not as much as it would. The reason to do this is so you can have a thin oil at low temperature for cold starts and not end up with a really thin oil at high temperatures that leaks all over the place. This is where the kind of rating 4w40 comes from and it means that at low temperatures (ambient?) the oil will have a viscosity of a grade 4 oil and at high temperatures (running temp?) the oil will have the viscosity of a grade 40 oil. Remember the number does not denote the actual viscosity it only tells you what grade of oil the synthetic oil is behaving like at the given temperature. For example a synthetic oil could actually have the same viscosity at low and high temperatures. Essentially it means the effective grade of the oil changes with temperature so its like having multiple grades of oil within one oil and picking the grade you want for a given temperatre to give you the viscosity you need. Its very clever stuff.
Another thing to note is that the charachteristics of an oil go beyond viscosity. For example if you take a fully synthetic oil and a synthetic oil of the same viscosity a fully synthetic oil will have a greater tendency to leak through gaps due the synthetic oil having a greater surface tension (im not sure exactly what you call it). For example this is what causes water to form globules rather than spread completely flat, on your windscreen for example, whereas oil tends to flow out flat. I think a synthetic oil has a greater surface tension than fully synthetic oil and thus should help stop leaks.
tr7v8
New member
Barks944 I don't understand this.
An oil rating is just that if you had a SAE 40 oil (mono grade but I know it doesn't exist) that means it has a given viscosity at a set temperature.
This viscosity applies whether it is lemonade, petrol, mineral oil, synthetic or whatever. An SAE 40 Synthetic has the same viscosity as an SAE 40 Mineral.
The reason that people frequently complain about oil consumption with synthetics is twofold
A. It used to be the case that most synthetics are lower viscosity so most were launched as 5/40 or 0/40 or even 0/30 although that did change later
as performance oils were launched like Castrol RS20/60. They were designed for low fuel consumption & very tight tolerances used in modern engines.
Synthetics also give longer intervals between services so less cost for the fleet market.
B. Synthetics are very good at scouring the engine clean, this tends to remove carbon deposits & therefore seep past rings & seals that were not an issue before.
An oil rating is just that if you had a SAE 40 oil (mono grade but I know it doesn't exist) that means it has a given viscosity at a set temperature.
This viscosity applies whether it is lemonade, petrol, mineral oil, synthetic or whatever. An SAE 40 Synthetic has the same viscosity as an SAE 40 Mineral.
The reason that people frequently complain about oil consumption with synthetics is twofold
A. It used to be the case that most synthetics are lower viscosity so most were launched as 5/40 or 0/40 or even 0/30 although that did change later
as performance oils were launched like Castrol RS20/60. They were designed for low fuel consumption & very tight tolerances used in modern engines.
Synthetics also give longer intervals between services so less cost for the fleet market.
B. Synthetics are very good at scouring the engine clean, this tends to remove carbon deposits & therefore seep past rings & seals that were not an issue before.
Say you take a grade 40 oil. Its going to be very thick when its cold but good at higher temps. That's fine but you make a sacrifice when the engine is cold. Take a grade 5 oil, nice and thin when its cold but really thin when its hot and will cause leaks. What you want is an oil that acts like a grade 5 at low temps but a grade 40 at high temps as that way you get the best of both. That's what the additives in synthetics do, they make the oil change in grade with temperature.
tr7v8
New member
That is what EVERY multigrade oil does, absolutely nothing to do with it being synthetic or not!
That is why my Valvoline is called 20/50 & this is a mineral, assuming your not running anything made pre-war then none of the oils "our" cars use is a monograde oil.
The additives keep the oil in grade & also give detergent abilities etc. Some of the additives will be zinc which protects high pressure areas such as the cam & followers.
Zinc is being reduced in modern oils because it gives issues with Catalytic converters, another reason why older style oils 'may' be better.
That is why my Valvoline is called 20/50 & this is a mineral, assuming your not running anything made pre-war then none of the oils "our" cars use is a monograde oil.
The additives keep the oil in grade & also give detergent abilities etc. Some of the additives will be zinc which protects high pressure areas such as the cam & followers.
Zinc is being reduced in modern oils because it gives issues with Catalytic converters, another reason why older style oils 'may' be better.
Isn't calling it multi grade just describing the fact that it behaves like different grades of oil at different temps? If so what is it that causes it to be multi-grade?
Edit: wiki says additives called viscosity index improvers are what make an oil multi grade. So its nothing to do with it being synthetic but it is down to the additives to make it multi grade. Synthetic oils are chemically constructed oils rather than being mineral oils. Semi synthetics are a mix of mineral oils and synthetic oils.
Edit: wiki says additives called viscosity index improvers are what make an oil multi grade. So its nothing to do with it being synthetic but it is down to the additives to make it multi grade. Synthetic oils are chemically constructed oils rather than being mineral oils. Semi synthetics are a mix of mineral oils and synthetic oils.
Hilux
New member
Its not its just that a thicker oil doesnt run off the surfaces.
Slowly but surely the truth will out. Of course thin oils in an engine designed for 20-50 will drain down at cold temps, they are designed to be more viscous at low temps!
IIRC Mobil 1 is a `cracked` mineral oil and not fully synthesised.
944 man
Active member
Yes, but Mobil only came clean when they were caught out. I believe that they claimed that it was a 100% ester-based oil, until the results of a gas spectrun analysis revealed that it was indeed mineral oil based. This is quite legal though because the term 'synthetic' carries no real meaning.....
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