Porsche Enthusiasts Club Forum

AFAIK none of the GTXs are semi Synth they use some clever words but they are all minerals. Edge is Castrols normally name for their true synth products. Having said that GTX will be fine in a n/a 944.

You're probably right with the clever wording, I suppose they could put a teaspoon of synthetic in 4 litres of mineral oil and call it semi synthetic. I know I've seen it for 40 years on the shelves of car accessories shops and it's always been called Castrol GTX in a white container. It used to be in 5 litre containers though, I suppose 4 litres is the value added by being in Europe now

Although not a Turbo I have just changed the oil in my 1991 S2 (106K miles) as it was a year (5K miles) since the last change, I have tried most of the oils from Mobil 1 0W40 to Castrol Edge 0W40 and Castrol RS 0W40 also tried Mobil 1 15W40 and Castrol Magnetec 10W40. The car always sounds tappety when cold or just started and has done from when I got it, I know the cam followers probably need doing but cant bring myself to do them.

Anyway tried Silkolene Pro S 5W40 this time as it had been recommended to me and the car seems quieter on start up and certainly quicker to quieten down so works for me. Bought from Opieoils when they had the Spring discount on last week.

I have never had any issue with tbe car using or losing oil indeed I probably only put about 1/2L into it over 12 months and 5000miles so not using much so I have not suffered what some people have related to usage either from using a synthetic or low viscosity oil. Indeed as I know the oil does not sit in top of the engine for long after switch off I would rather it be thin enough to get up there quickly on start up than too thick and I would suppose once warmed up most oils are similar viscosities.

Thanks David

Always good to hear a tried and tested.

Peter

We recommend Mobil-1 Motorsport 15w50 for 944 Turbos .. Silkolene is ok too (I just prefer Mobil-1)

Never heard any source saying Mobil kills turbos, been the official Porsche oil for years and you will be hard pushed to find anyone claiming Porsche turbo's blow up through anything other than a fault outside of the turbo (typically on 944 turbo's its the airbox that kills the turbo! Never even had to change one through old age!

You can use MobilS 10-40 as well, another good oil but not fully synthetic. Which I prefer in a turbo

Also need to remind people that the 944 Turbo should have the oil changed every 6 months (as any car should in my opinion but thats a whole new discussion/argument!)

Your absolutely spot on for the whole "Semi synthetic" thing.. there is a real industry problem because a tiny amount of synthetic additive even in a 200L drum of synthetic allows people to call it synthetic. So you do have to watch some semi synthetics, typically the more dubious brand ones.

Thanks, that's really helpful.

Out of interest what goes wrong with the airbox? Does debris or something get sucked into the turbo? Maybe I should invest in a cone style filter something like the K&N type.

Where the airbox screws together, eventually the lugs break, causing either small bits of plastic, or (even worse) the captive nut, to be sucked into the turbo... a turbo that at the time is probably spinning at 140,000 to 190,000 rpm... the compressor wheel fins tend to then break up, partly through impact, partly through imbalance.... result is a new turbo and sometimes a new engine..

Cone filter is a good idea and has the side effect of improved performance... a new airbox avoids the problem, just make a choice as soon as you see cracks, repairs or issues around the airbox lugs.