Semi or fully synthetic oil..which one?
- Thread starter Axl Rose
- Start date
Diver944
Active member
This is not strictly true if you use the correct oil rating. If you fill with a very thin 0W30 or 5W40 then yes you will burn a lot as our cars were not designed for oil that thin. Stick with 10w40 or even 15w50 if your engine is a bit 'worn' and you'll be fine
The advantage of fully synthetic oil is it does not break down under extreme heat like a semi-synthetic will. A N/A car does not need a fully synthetic oil but a Turbocharged car will do as the heat around the turbocharger is immense and will eventually break down a semi-synthetic oil
ORIGINAL: edh
I reckon your pressure sensor is dodgy then
That's not far off what my old 2.7 used to read, once warm it read almost 5bar driving & about 3-3.5 at idle. Could just be that I never really got it hot (enough) but in normal driving particularly on short trips it's in the same ballpark as mine was.
My current 250 turbo give a constant 4+bar once fully up to temperature (it's probably about 4.1, 4.2), and just over 2 at idle. Right at the end of the day at Bedford I was caning it & the oil pressure dropped a little to about 3.5 or thereabouts, I guess I cooked the oil.
I use 15w40 semi synthetic, I'm thinking I'll try fully synthetic at the next oil change but my car already consumes oil at a fair old lick [
]
Neil Haughey
New member
Maybe not that far out, it depends on usage. Mine went to about 2 3/4 bar after the afternoon dry sessions at Bedford race track. After 30 minutes crawling through Exeter traffic it only went down to 3 bar, and then after a short drive the other day was 4 bar at idle. You may have to give it some serious stick to get the oil hot enough to get a low reading. Drive harder!
Neil Haughey
New member
According to Opieoilman (pistonheads name) the newer oils such as Silkolene pro S are superior to Mobil 1. ISTR he recommends 5w-40 in the 968 and 10w-50 for turbo's or S2's that are tracked hard.
Can't understand why people would go for anything less than fully synthetic these days - it's like arguing that Castrol R is the thing to use because that's what they put in a Lotus 49.
As far as weight goes - anything below 10w is likely to cause issues for being too light. It will find and open up seals causing leaks in places you never knew were there. I have heard of Porsche 4 pots being damaged by using 0w/40 for this very reason.
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. This being the case I now use Mobil 1 15w/50. It isn't as easy to find as 0w/40 so I tend to buy it when I see it.
As far as weight goes - anything below 10w is likely to cause issues for being too light. It will find and open up seals causing leaks in places you never knew were there. I have heard of Porsche 4 pots being damaged by using 0w/40 for this very reason.
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. This being the case I now use Mobil 1 15w/50. It isn't as easy to find as 0w/40 so I tend to buy it when I see it.
TTM
Well-known member
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.
pauljmcnulty
Active member
I was told that my old-fashioned 8v NA engine was better run on semi-synth, just as a turbo should never be run on anything less than fully-synth due to the high temperatures in the turbo itself?
Don't really understand the science, but do trust the guy who puts it in! [8|]
edh
New member
Mine dropped quite low at Donington this weekend - after 20 mins or so of track use it was falling to 3-3.5 bar at 4k. It's been fine on the road, just track use that really heats the oil.
I checked with Zentrum - when they did my headgasket, they refilled with 10w40 [] - I had asked specifically for 10w60
That'll be going before long - I guess it's given the engine a flush though []. I'll try some Mobil 1 15w50. Millers 10w60 is good stuff if you can find it - and cheaper than Mobil 1.
I checked with Zentrum - when they did my headgasket, they refilled with 10w40 [
] - I had asked specifically for 10w60 That'll be going before long - I guess it's given the engine a flush though [
]. I'll try some Mobil 1 15w50. Millers 10w60 is good stuff if you can find it - and cheaper than Mobil 1.
It's a bit like using P6000's - You can, and they will stop the wheels scraping on the tarmac, but there are better options about. [
]Years ago people used Duckams oil. It was then found that it varnished the inside of the engine (good for garden gates - not good for engines). Technology moves on. It seems daft not to make use of that technology.
Synthetic oil is more slippery, more resistant to shear and has higher tolerance to heat. Why wouldn't you use it? It is more expensive but, if you consider how long it is in the engine, it isn't that much more per mile.
Re: 10w/60. When I had an engine built by Dunnell Race Engines it was guaranteed against failure provided I used Castrol RS 10w/60 and only Castrol RS 10w/60. One assumes Paul Dunnell knows what he is talking about, and for that reason I used to use RS 10w/60 on all our cars. Mobil 1 is easier to get hold of though.
ORIGINAL: edh
Mine dropped quite low at Donington this weekend - after 20 mins or so of track use it was falling to 3-3.5 bar at 4k. It's been fine on the road, just track use that really heats the oil.
I checked with Zentrum - when they did my headgasket, they refilled with 10w40 [
That'll be going before long - I guess it's given the engine a flush though [
I'd be interested to learn how you get on, looks like we have similar symptoms with similar oil.
I always use fully synthetic and go by the following rule, minimum first number, maximum second number. The ultimate would be 0W-60 if you could get it. The first number is low temperature viscosity, it's important this is low (indicating low viscosity) so that it quickly circulates and protects on start-up. The second number is better high if engine protection, high oil pressure, preventing oil leakage and low oil consumption are your priority (rather than an extra fraction of a per cent of fuel effieciency). This indicates a relatively high viscosity at high temperatures. It should be pointed out that even a 0W-60 oil is still at it's most viscous at low temperatures so any worries about the 0W causing leaks are groundless. It's having a low second number that could cause oil leakage.
I used Castrol RS 10W-60 in my 924, it gave excellent oil pressure (protection) and never required topping-up between changes. I've not been able to get this recently, so 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.
I used Castrol RS 10W-60 in my 924, it gave excellent oil pressure (protection) and never required topping-up between changes. I've not been able to get this recently, so 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.
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