I recently bought a
2008 Cayman S
. The old owner said they always used 95 octane fuel, and I have been doing the same over the past couple weeks, but reading the owners manual, it recommends 98 octane for best fuel efficiency and performance.
I had a bore scope, compression test, and leak down test done as well as a PPI before buying the car and all came back perfect with the exception of the brakes being 40-50% worn. Mechanically the engine was in perfect condition which given the cars milage (65,000 km) makes me question whether 95 is hurting it.
So my questions are: Should I switch from using 95 to 98 octane? Would it delay/prevent damage such as bore scoring? And would the increased fuel efficiency of 98 cost less over time than 95?
The last question isnt nearly as important to me, as my primary concern is preventing damage to the engine.
I believe your octane numbers are calculated differently than ours in the US. Here, the recommended octane is 93. The car will adapt to lower octanes, though, to prevent pre-ignition (knocking). Your car will do the same.
The bore scoring issue is not related to octane, and your choice of gas will not harm the engine. I doubt mileage would be affected, since your driving style plays a much bigger part.
I would recommend using the proper octane fuel as well as using a “Top Tier” brand. Perhaps the top tier designation is not used outside of the US, but basically you want a fuel that has more than the standard additive mixture required by law.
Poor quality fuel can certainly lead to bore score. In a nutshell what happens is the fuel injectors can get contamination so that the fuel spray into the cylinder is not even. Then some of the fuel isn’t burned properly and gets on the cylinder wall where it prevents properly lubrication of the cylinder wall with engine oil.
Here is a PCA video which discusses the topic and there are others as well.
Where I am (New Zealand) I believe the octane rating at the pump is the RON number, whereas in America, there is some calculation done with the RON number, the result of which is the number on the pump.
As for 'Premium Fuel' or 'Top Teir Fuel', I believe fuel here is regulated to the point where all gas stations sell the same fuel regardless of how or if they market it as 'Premium'. From what I've seen, 'Premium' just refers to any octane fuel of 95 or above. There may be a tiny amount of additives but no amount that would make any difference.
With this in mind, the owners manual states:
Your engine is designed to provide optimum performance and fuel economy using unleaded premium fuel with an octane rating of 98 RON (93 CLC or AKI). Porsche therefore recommends the use of these fuels in your vehicle.
Porsche also recognizes that these fuels may not always be available. Be assured that your vehicle will operate properly on unleaded premium fuels with octane numbers of at least 95 RON (90 CLC or AKI), since the engine’s ”Electronic Octane™ knock control" will adapt the ignition timing, if necessary.
In NZ, the 95 and 98 RON numbers are what is displayed at the pump, and currently I am using 95. Would there be any benefit in engine health of switching to 98 Fuel?
Not in engine health, no. You may get a bit more power because in certain situations the car will be able to run more ignition advance with the higher octane fuel, but it's not that big a difference.
That said, if I could get it I'd run it. Highest octane we generally get in California is 95/91. Doesn't cause any problems, though.
