Unless you've read your owners manual from start to finish, you'd probably be surprised to find out that many manufacturers recommend using a higher octane petrol in high and cold temperatures. When I heard this myself, I was skeptical, until I pulled out the manual, wiped off the dust and began reading through. How have we not been told this before?
As it turns out, it's true. Manufacturers are recommending PREMIUM gas when operating in ambient temperatures below -10°C or above 28°C. Some never models even recommend the costly petrol above 25°C. Here's what's in my Volvo manual:
A higher octane (at least 97%) fuel should be used when outside daylight temperatures remain under -10°C or above 30°C
Well that certainly was news to me. Here's the logic behind it: Small engines, especially turbocharged engines, are extremely fine tuned for performance and fuel economy. The thicker oil mixed into petrol can become blocked and un-burned when it passes past the ignition.
Old american cars we're built to use 80% Octane fuels, but they were large and naturally aspirated V8s in which economy or refinement wasn't really an issue. These days, cars must adhere to emissions, economic performce and several other factors which make them more complicated, more refined and ultimately harder to maintain.
This is hardly good news given the current price of gas per litre, but every cloud has a silver lining as they say. In theory, you should get better fuel economy and a touch more power when using premium 98% Octane petrol in the summer months. Doubtful that the savings will outweigh the extra cost though.
What are your thoughts? Do you use Unleaded 98 in the summer months?