Which Oil

[Guest]

As the title suggests what Oil is recommended for our cars, I've got loads of Mobil 1 0w-40 in the garage, is this Ok or does it need a different grade ? Wheres the best place to get a filter is it specialists as discussed on other threads or would someone local like Halfords be able to source them ?

Mike

17 hours and counting []

 

[paulf968]

Mike

There are lots of discussions about oil for 968's. I looked into it and reached my own conclusions as follows.

0-40w fully synthetic stuff is by all accounts far too runny for this type of engine -- that is because it is an old design and the oilways are too wide.

I thought long and hard about semi-synthetic types around the 10-40w rating but in the end opted for Mobil 1 'Motorsport' grade also fully synthetic and 15-50w. It is probably the most expensive oil to consider -- with 6.5 litres there is no change out of £50 -- I think it is cheap insurance.

So if you have lots of the ordinary Mobil 1 stuff (unopened) then could I suggest that you might be able to do a straight swap at your supplier for the Motorsport variety -- assuming they stock this version. That would solve the problem in one quick move--thereby freeing up cash for other goodies you will want to buy.

Filters I am much less fussy about, my local cheapo spares place offers Mahle oil & air filters (Austrian) and they appear to be well made so I use them and save a load of cash.

ps sounds as if your are ready for an early trackday after your little collection trip tomorrow. I am told one or two spaces may have come free on the 28th at Bedford -- get your credit card out.


paul

 

[Guest]

Oh well the Mobil 1 can be used in the wifes little Ford Ka, it won't know whats hit it []

As for the trackday mmmm very very very tempting, but really I want to make sure all is OK before taking her on a thrashing session so next time if the price is right []
Also I really want some spare wheels first so I don't end up burning decent rubber ragging around a circuit, I tend to save my takeoffs when changing my road tyres just for this purpose.

The credit card !! well this month the less said the better Jan/Feb is always tight especially when buying cars [&:]


Don't worry we'll meet on circuit sooner or later I'm sure, and I'll be after some pointers on throwing the 968 around [8D]

Mike

 

[Rob Sharp]

Mike,

I've been round and round this one, and the short answer is you'll never get a straight answer!

However, for what it's worth I've consulted various people including an OPC, my Porsche specialist (Hartech) and my brother, who's owned and run his own motor engineering business for the last 30 years. Naturally they don't agree on everything but there's definitely a band of oils that seem to win the majority of opinion.

As Paul said, everyone seems to agree that Mobil1 0w-40 is too thin because the engine design is older, so at least your wife's Ka will benefit.

Until I bought it, my Porsche has always run Shell Helix Ultra 5w-40, but on suggesting this to the three parties, only one - the OPC - said it would be OK. Various mumblings from the others suggested that since the engine's now done a fair few miles, this might also be too thin and there would be some risk attached to using it.

General concensus opted for a 10w-40 grade - all agreed that this was fine. Hartech use the semi-synthetic Castrol GTX and I know others go for this too, and in the end, that's what's in my car. Only my brother, who has a pathological dislike for Castrol oils wouldn't support the choice of GTX, although he does agree the viscosity is right.

Regarding the Mobil1 15w-50 oil - this was considered too thick for the 968's engine - "viscosity way too high". Note: this is all greek to me - I'm just passing on the message!

My only regret is that no-one seems to make a 10w-40 fully synthetic oil - at least not the last time I looked.

Hope this helps!

 

[Melv]

" Mobil 1 'Motorsport' "

Had a long chat with a Mobil rep about this at Goodwood a few years ago. For us souls with older engines and larger oil ways, this is preferable to 0-40W, which is designed for newer engines with smaller oil ways.

Apparently there was a court case regarding recommendation of Mobil 0-40W by the Escort RS Owner's Club that led to loads of turbo failures.

Don't quite understand the comment about too high a viscosity. The only difference I found in my old 944 was that during the winter it started easier with a low oil level than full. I can but assume the big ends were splashing around in less oil?

Mel

 

[Mark_Bennett]

My only regret is that no-one seems to make a 10w-40 fully synthetic oil

How about a 10w-30?
Available in.... Australia!

 

[Guest]

Hmm lots of different views, what to do ?

I think I'll probably split the difference and go with a 10w40 for the time being.


Cheers

Mike

 

[Guest]

Bugger, i've just booked a 12k service and GT One in Chertsey say they use Mobil 1 Sport 15/50 for the 968. mumble mumble....

De

 

[Mark_Bennett]

Derrick,
That sounds perfectly reasonable. What does it say in your handbook for permissable oil weights?

The 968 from the start of the 1993MY (i.e. Sept 1992) left the factory filled with Shell 5W40 synthetic. But the handbook will say the allowed "fill" types.

 

[944Turbo]

the 944 handbook says that 15/50 is fine for temps down to minus 10, then thinner required. I have been using motorsport as the original runny stuff dissapeared too quickly, however for availability reasons last change I went to runny tri synthetic mobil 1, this seems to stay in much better then the original runny stuff. Also don't really see the large / small oil way argument - well I can see thick stuff might not like thin oilways but dont see a problem of runny stuff under pressure in big oil ways.
Tony

 

[Melv]

"dont see a problem of runny stuff under pressure in big oil ways."

But it is -thinner stuff can run through seals and gaskets and go where you don't want oil to go.

Melv

 

[paulf968]

To add another comment to the debate, I think there is another aspect that makes runny stuff unsuitable.

If it is too runny then reduced back pressure is experienced in the oil ways. IMO this will mean that the oil will then take the 'easiest' route out to the sump. As a consequence the furthermost points in the oil pathway network may experience lower pressure or even some starvation.

I do not know which of the oilways are furthest from the oil pump but it might be the overhead camshaft & chain and that is just the sort of place where 968's definitely need a good supply of oil. So 10-40w is in my opinion the thinnest grade of oil that should be contemplated for a 968, in UK conditions.

Question -- for harder use of the engine, say when 6000rpm is used regularly, on something like a track day, are there any other things that should be considered with the choice of oil?

paul

 

[Guest]

Apparently reading between the lines in my German service book and receipts mine has been used to 0w30 and more recently in the UK Mobil 1 0w40. My engines done 135 thou and still sounds sweet so it can't be that much of an issue running a low viscosity oil.

Mike

 

[Guest]

A bit of info gleaned from one of my MG buddies in the Oil industry.



What is the importance of viscosity in my engine?

The viscosity will determine how easily the oil is pumped to the working components, how easily it will pass through the filter, and how quickly it will drain back to the engine. The lower the viscosity the easier all this will happen. That is why cold starts are so critical to an engine because the oil is cold, so relatively thick.

But, the lower the viscosity, the less the load the oil can support at the bearing on the crankshaft. The higher the viscosity, the better the load support. Even this, however, has a trade-off, since the higher the viscosity, the more the drag at the bearing, and hence, potential power loss. So a compromise is chosen to minimise power loss, but maximise load support. Stick to the recommended viscosity for your engine.

For domestic use, engine life is important. For motorsport, engine life is not critical, winning is, so these high performance engines use lower viscosity oils to maximise power output to the wheels.



How is viscosity rated on an engine oil?

The Society of Automotive Engineers (SAE) developed a scale for both engine and transmission oils. The measurement is undertaken in a laboratory in accordance with the American Standards and Tests Methods (ASTM) and is usually rated from 0 to as high as 60 for engine oils and from 75 to 100 for gear oils. A 40 engine oil has a similar viscosity to a 90 gear oil.

Typical steps are 0W, 5W, 10W, 15W, 20W, 30, 40, 50 60 for engines and 75W, 80, 90 and 100 for transmissions.



What is a multi-grade oil?

Until the early 60's, most oils were a mono-grade, typically either a 30, 40 or 50 grade viscosity. The higher the ambient temperature, the higher the number used. This did mean that a cold start could be quite damaging for an engine, so in Winter, the oil would have to be drained and replaced with a lower viscosity oil.

Multi-grade oils were developed to allow year round use. They are typified by a two number system with a W. For example, 10W30. The first number refers to the viscosity of the base oil used, and W is generally understood to mean Winter (although some suggest W for Weight of the base stock). To achieve a useful viscosity at operating or warm temperatures, the 10W has additives (also known as Viscosity Index Improvers), which are like tightly wound coils that unwind as the oil warms up. The expanding coil causes the viscosity to increase and perform like a thicker oil. However, over time, these additives become susceptible to shear and lose some of their performance.

Historically, with older engines having looser clearances, and especially in the Mini/1100's with the gearbox in the sump, these engines still generally require a thicker oil such as a 20W50 or 15W40, unlike modern cars which run on 10W30 or even 0W30.




I think the last paragrapgh is probably the one we're interested in "older engines"

Mike

 

[Buddy]

When I bought my 968 from 911 Virgin, it was serviced and filled with a Castrol 0-30 but consumption was minimal though I wouldn't recommend the garage who did the service as they broke the locking wheel nuts and wanted me to pay for a new set, overhauled the front brakes at £500 and fitted number plates (which were needed due to a change of reg') which had their name on.
I didn't like the idea of using such a thin oil and so when 6K were up I had it changed for the same oil I had used in my 944 turbo, Quantum Synta Gold 5-40 which I find equals any other good oil that I have used and although the turbo had been used to mineral oil, the Quantum, being fully synthetic stood up to the temperaures of the turbo better than the minerals.
The problem with using too thick an oil in modern engines is that the hydraulic tappets can 'gum up' their oil feed holes are small and so a thin synthetic will perform better for this application, I think that 0-30 is too thin for bearing loads in high compression engines but 15-50 is too thick for the tappets after that it comes down to brand choice, Mobil 1 is excellent but expensive, Porsche are listed for use on the back of the Quantum can.

 

[John H]

and fitted number plates which had their name on.

That is now a legal requirement, supposedly so that suppliers of number plates can be traced, to help stop cars being "cloned".

Quantum? Isn't that VW's own make? I use the Synta Gold in my VW and it seems good, and it can also be bought surprisingly cheaply from certain VW outlets, as well as in bulk at VW rallies. Good idea, I might switch to this myself.

JH

 

[John H]

For domestic use, engine life is important. For motorsport, engine life is not critical, winning is, so these high performance engines use lower viscosity oils to maximise power output to the wheels.

Eminently sensible and understandable. So why the hell do Mobil use the term "Motorsport" for the thicker version of Mobil 1. I have never understood this, and indeed it has put me off using it.

JH

 

[paulf968]

Yes, that point about thicker Mobil Motorsport oil is a bit of a puzzle but the understanding I have is as follows and is at odds with the above quote.

For road use the most significant difference with the Motorsport grade is the 15w rating (ie the rating at normal air temp say 10 to 20 degrees C), the difference at the hot rating from 40w up to 50w at 100 degrees C is not as significant. So for older engines made to less tight tolerances 968 owners would usually go for the Motorsport 15-50w, that is at cold the oil is held better on surfaces.

Now the point about racing, usually a racing engine is made with a looser fit to minimise friction eg smaller pistons with less contact area. This probably at the expense of a longer life. In such circumstances oil film thickness at high temp becomes more important hence the need for a 'heavier' grade. ie the oil covers and clings a bit better when there is a looser fit and at higher constant temps.

I think that is an explanation, anyone got a different thought?

paul

 

[John H]

I was in Halfords today buying windscreen wipers, and noticed that for some reason they are selling their own brand 5/40 fully synthetic oil at £14.99 for 5 litres. Compare this to the Mobil 1 Motorsport 15/50 at £2.99 for 4 litres.

Think I'll go back and buy some!

JH

 

[Guest]

I saw this the other day too, sounds too good to be true but at that price you could afford to change it every 5K.

John 2.99 for 4L of Moby 1 ??? have you been on the juice ?[]

Mike