Semi or fully synthetic oil..which one?

[John Sims]

ORIGINAL: knightma
.... I'm about to use Mobil 1 0W-40 in my 944, so I'll see how that goes. For me the most important factor is the 0W. The majority of engine wear occurs on start up for the first few revs before the oil has circulated, the lower the cold temperature viscosity is, the quicker it will circulate and begin to protect.

No don't! See my note above. 0w is too light for the type of seals employed on our old technology cars and will start leaks.

Multi grade oils (those noted as 0w/40, 10w/60) are rated as follows:-

eg 15w/50

15w means this oil will have the same viscosity as a 15 weight oil when it is cold (ie a 15 weigh is quite thin but obviously thicker when cold but not as thick as a 50 weight when cold)

/50 means the oil will have the same viscosity as a 50 weight oil when hot

Now because multi grade is less viscous when hot we can assume that hot 50 is thinner than cold 15 for example. But is hot 50 less viscous than cold 0 ?

Also, when the engine is working it is nice and hot so everything is bigger and there is pressure pushing seals closed. When it is cold, and not running. the tolerances on the seals are much bigger (and they aren't pressurised) so thin oil can escape around them.

 

[Riverside]

ORIGINAL: edh

The car was running on Millers 10w60 and Castrol RS before - never had any oil pressure problems on trackdays

I had a 924S with 200k on the engine - Millers raised hot (track) oil pressures by at least 1 bar.

I'm not far from Derby, where could I get it from?

Mine uses quite a bit of oil so I've been reluctant to go with anything much thinner than 15w40, what's your oil consumption like?

 

[944Turbo]

time for a handbook extract (again)

 

[knightma]

ORIGINAL: John Sims

But is hot 50 less viscous than cold 0 ?

John,

0W-50 oil has the following temperature viscosity relationship (approximately)

-18°C 4000 centistokes (cSt)
0°C 1000 cSt
20°C 400cSt
100°C 25 cSt

Hence a 0W-50 oil is far less viscous when hot than cold, hence my point that leakage will be more of an issue for an oil with a low second number i.e. low viscosity at high temperatures.

 

[edh]

ORIGINAL: Riverside

I'm not far from Derby, where could I get it from?

Mine uses quite a bit of oil so I've been reluctant to go with anything much thinner than 15w40, what's your oil consumption like?

I don't usually use much oil - although can use a bit on trackdays. On a dry day, probably can go from max to min on the dipstick. Interestingly I didn't have a pressure problem in December @ Donington with this oil - maybe it just hasn't lasted very long. I've used about 1l in the last 1500k, mainly road use - I think some of that has blown by the turbo seals. I don't think there's any reason to go thinner myself.

Not sure about local supplies - I have a friend who get me the Millers at trade price

Just bought some Mobil 1 15w50 from Merlin Motorsport mail order with some other stuff

Opie oils are usually quite cheap & post regularly here

 

[944Turbo]

Don't let it get near minimum on trackdays

 

[edh]

I try to check the level after each session - I reckon on topping up 2-3 times on a full day

I hardly used any last weekend - I think because it was very wet.

 

[John Sims]

ORIGINAL: knightma
.... hence my point that leakage will be more of an issue for an oil with a low second number i.e. low viscosity at high temperatures.

You would think so; except, when the oil is hot the engine is hot, and the seals are supple, so all those nasty tollerance gaps have closed up nicely.

 

[Peter Empson]

ORIGINAL: edh

I don't usually use much oil - although can use a bit on trackdays.

I think the record on my old engine was 3 litres on one trackday. I did like to do my bit for the environment []

 

[jr2015]

ORIGINAL: britaxcooper

on the gauge, doesnt drop below 4 really at idle.
mine (and my dads) is running fully synthetic, and the oil pressure is always on 5
Whats recommended for a turbo?

Maybe you`ve got the original Oil pressure sender gasket under the one that was fitted with a replacement sender, they tend to stick to the housing when the old unit is removed and cause an artificially high reading.
jr

 

[sawood12]

I use 5w40 Silkolene pro in mine and have no problems at all with leaking. The car uses virtually no oil on road use (but uses some on track) and my pressure is alway above 4 - even on track. Not sure what this means and if I should continue using this particular grade but my philosophy is you want to be using as low a viscosity as you can get away with. Machines work better with thin oil - but obviously not too thin. I use the 5w because I want good cold start protection. I would have though that a 60 viscosity oil would not be ideal for normal road use. I thought that you'd use a 50 or 60 viscosity oil in high temp situations e.g. heavy track or race use where the oil runs hot and is probably as thin at elevated operating temps as a 40 viscosity oil is at 100 degrees, as the viscosity rating is the viscosity ratin of the oil at 100 degrees C.

Incidentally I agree with previous comments - why use anything other than fully synth? What possible advantage would mineral oil be in any car? And semi-synthetics have been exposed as being a con - they are virtually a bog standard mineral oil.

 

[333pg333]

ORIGINAL: TTM

ORIGINAL: John Sims
I was a great believer of Castrol RS10w/60 but have been told that the viscosity modifiers necessary to obtain 60 weight break down very quickly and it becomes 50 weight in very little time.

I'm not sure why 10W50 would make a great deal of difference to 10W60, especially with an oil as good as the Castrol RS. This is the oil that was once vocally recommended to me by a former official Turbo Cup mechanic and confirmed by another one no later than two weeks ago.
My Turbo has got about 180k miles with it original bottom end and turbo and doesn't drink any oil at all unless I strongly and repeatedly use boost ; pressure on warm idle never ever gets below 3.5 (the turbo does not smoke at all, btw), all with RS 10W60.
The Castrol might well have been surpassed by some other oil but it remains an excellent oil for our cars and it still deserves a mention IMHO.

FWIW the German 944/951 enthusiasts have raved on the Castrol endless but now talk about Valvoline VR 20W50 as it's quite cheaper. I'd like to try it but in this diseasel-infested country I cannot find any of it.

This is good info and I'd trust those guys who use the Castrol. We use 25/50 but don't have to worry about the cold start as much as you guys. A full synthetic, light W oil is not best for our cars and appears to be the common denominator for most engine / bearing failures that we have noticed.
Also don't forget that your oil is designed to protect your cars internals by forming a sort of suspension between the moving metal parts. It's not just a matter of it being 'oily' and lubricating, it buffers between the expensive bits. Having these low viscosity synthetic oils on the track is pretty dangerous especially with the propensity of our cars for spinning rod bearings and not much in the sump of a stock car to prevent oil starvation under high loads on the track. I don't think there is a magic oil that is perfect. If this were true we'd all just use a 0/60w and be done with it wouldn't we?
As an offshoot to this topic, do any of you guys run any sump baffles or windage trays/crank scraper etc even dry sump to prevent oil starvation?

 

[sawood12]

Yes but if the oil is too thick then the boundry layer between the static bearing and moving shaft will not form. Granted at higher temps that the oil gets to during hard and prolonged track use you need a higher viscosity oil because it thins down at higher temps but for street use a 50 or 60 viscosity oil might be too thick for the boundry layer to form. If the gap between the bearing and shaft is too small for a thick oil the boundry layer will not form properly which is why for small gaps you need a thinner oil. Even on a track day where you are doing 20 - 30 minute stints I reckon a 40 viscosity modern fully synth like Silkonene pro or Castrol RS should be perfectly adequate. 50 and 60 viscositys for more prolonged track use.

I think I might install a oil temp gauge and monitor the temp during my next track day. If it gets much above normal temp i'll probably fit a Kiss oil cooler before moving to a 50 or 60 viscosity oil as my car does 98% of its milage on the road.

 

[333pg333]

Scott as far as a standing or static layer is concerned, my mechanic has taken the cam box off a 928 that has been standing in their workshop for a few days and which has always run Castrol 20/50w and it has done almost half a million km's and basically the cams look almost brand new. They can wipe oil from the cams after all this time standing. Wheras the cars with the thin oil is virtually totally dry.
Almost every car that we've heard of that has had the engine blow, has been running on Mobil 1 average 5/40w. When M1 first became popular and was buoyed by a massive advertising campaign many of the local Porsche mechanics naturally switched. Within a year some started switching back as they had a sudden increase in wear and failure. Maybe this is all coincidental...maybe not?
As for gauges I think oil temp and pressure are vital. I've got one of those Spa twin gauges waiting to be installed along with the Zt2 wideband. Not that this is to do with oil, but it's a tuning and protective product too.

 

[sawood12]

I was referring more to the boundry layers that form when the engine is running but I take your point about engines that have been standing. However one of the reasons I went for Silkolene pro over something like Mobil 1 is that it is an Ester oil which means the oil particles have been polarised and therefore magnetically cling to ferrous surfaces so bearing surfaces should never drain down as there will always be a thin film of oil that clings to the ferrous metallic surfaces. Mobil 1 is not an Ester oil so the oil will totally drain down and leave bearing surfaces dry. In my mind it is essential to have an Ester oil and cannot understand why you wouldn't use this type of oil. It is pretty well accepted that engine wear occurs in the first 20mins or so of each journey as the oil is comint upto temp and therefore getting into the effective viscosity range. With an Ester oil with a low w rating you will have some protection in that phase of each journey. With high viscosity oils (50's and 60's) my worry is that even at normal operating temp on the road the oil still wont have thinned down to a viscosity level that offeres the best protection. Fair enough on the track the oil achieves higher temps therefore lower viscosities and better protection.

I havn't really got a feel for how hot a 50 or 60 viscosity oil needs to get to before it is the same viscosity of a 40 at normal operating temps. Therefore my approach is to go for the lowest viscostiy that maintians oil pressure and that doesn't cause increased leaks. I am relying on the Ester properties and low W rating to provide cold start protection and the properties of a modern fully synthetic oil to protect me on the handful of trackdays I do.

 

[333pg333]

Yes I take your points on board. It will be interesting just to see how hot the oil does get on track once the new gauges are installed? I'm giving a dry sump system a go too, and that should help keep the oil temp down as well.

 

[smitty893]

Thought I would add my three pennies worth. Can't understand why anyone would use anything other than synthetic. as long as its the right grade - thin oils can't protect as well. Reminds me of the early 80's when I worked on Honda motorcycles - at the time they were recommending 10w30 oil (or something similar) we always used 20w50 and were one of the few dealers that didn't have issues with cams / followers or engines siezing

 

[333pg333]

The use of the term synthetic is a bit of a misnoma as all the base material is derived from the ground initially. There is no such thing as an artificial 'oil' as far as I know. What they do to it in the labs is a different story.

 

[Hilux]

As an offshoot to this topic, do any of you guys run any sump baffles or windage trays/crank scraper etc even dry sump to prevent oil starvation?

Sometimes I feel that the conversations get a little extreme. In my opinion the cars have got this far on all sorts of oil over their lives as most have done well over 100,000 miles [].

I would imagine most of the Vauxhall/Audi/BMW/SEAT/Honda etc spec oils will suffice, after all they are in every day cars that will be thrashed occasionaly, rev to over 8000 rpm and will have turbo`s and oil changes every 12K??

If you are a Porsche cup racer or a track day addict then yes, use a different oil based on others experience. If you are worried re oil surge/cavitation/starvation surely the best mod IMO is to brace the oil pickup pipe and extend it lower into the sump. I have a spare sump and this summer I am going to do this and baffle it as I'm not happy to wear slicks later this year without these simple mods. The other option is to extend the sump depth with a collar so more oil with a longer pick up is available.

I also note my max oil pressure (admittedly on the factory gauge) dropped to about 4 on track while the car was being ragged rigid. This is interesting as the oil is obviously warmer so I`d also like to know its temperature as then it `might` require a bigger oil cooler. Trouble is there`s no point in over cooling the oil at normal times if its only an issue on track?

Dry sumping is ideal but expensive and only really necessary for die hard slick shod track day warriors but cup racer cars arent dry sumped so I think I'll leave well alone[]

Discuss...............................[8D]

 

[sawood12]

Paul, I intend to fit an oil temp gauge to monitor oil temps on track days. Although i'm confident i'm getting adequate proteciton from my current 5W40 for normal street use I want to be 100% certain i'm getting adequate protection on track days. It seems a good idea to me to have a second oil cooler with a switchable valve so you only use it on track days and for street you can divert the oil via the normal circuit. I'm not sure about the feasibility of this as i'm not sure of the effect on the oil in the 2nd cooler for a long period of time while the 2nd oil cooler is not in use.