Which oil is the best for a car might be one of the most discussed topics in online discussion forums (case in point, the 1500+ post thread at Pelican parts). One problem when reading up on the subject is that it is very complex and that there are a lot of misunderstandings floating around.
After going through a slew of different sources I soon realized that finding a suitable oil wasn’t that hard but finding one that is readily available and not too expensive is a bit more tricky.
My choice finally came to Agrol Super Syntet. It is a fully synthetic 5W-40 SHPD (Super High Performance Diesel) oil . That means that it is originally designed for turbo-diesel engines in demanding applications typically found in trucks and other commercial vehicles but that also means it has some properties that are important in the air cooled engine found in a Porsche 911.
One important feature is a high flash point (226 deg C) since parts of these engines become very hot. It also has enough of important additives such as Zinc and Phosphorous, a nice viscosity index at 170 and a HT/HS at more than 3,5 cP.
Being a synthetic oil it can potentially cause problems with leaking seals but since I already have one that is leaking I might as well find out if there are any more that need to be attended to before fixing that.
For those that don’t want to try a synthetic oil, Agrol also carries a 15W-40 mineral oil that I think is suitable – Agrol Turbo Super (soon replaced by the similar Agrol Classic).
I like the Agrol oils because they are readily available and has a very competitive price. I payed SEK 80/liter for three 4 liter packs and they are also available in 20 liter packs that will lower the price a bit further.
[Update 2015] After discussing oils in more detail with the helpful people at Agrol I’ve stopped using Super Syntet, going for their semi-synthetic Nova oil instead. It has many of the qualities from the Super but is better suited to petrol engines. If you drive more than 15 000 km between oil changes, Agrol recommend the Spectra instead. Both of these oils are Porsche-certified.
If you are interested in reading more about this subject I recommend to start with these resources:
- Charles Navarros page about oil for air-cooled 911s.
- Penrite oils article about Zinc levels and engine wear.