Does premium gas matter on old Volvos Topic is solved

clarity · Post by **clarity** » 27 Mar 2004, 23:45

My mom and I both have older Volvo 240s, mine is an 84, hers an 88. We are having an argument whether premium gasoline actually does anything beneficial, especially in older cars. Anyone have a point of view?

afrobrick · Post by **afrobrick** » 28 Mar 2004, 15:00

premium gas (91+) octane is benificial for any car that is driven in a hot climate. i would say that if the car is driven a lot in temperatures above 80 degrees ferenheit, you should definately not use regular gas. one rule to know is that the hotter the climate, the higher the octane. also if it is a turbo, it is almost a must to follow the manufacturer's reccomendations and use premium gas. this is to prevent preignition which can kill an engine in just a few occurances. paying the extra 20 cents per gallon is worth it.

petershen1984 · Post by **petershen1984** » 28 Mar 2004, 23:15

High mileage vehicles tend to collect carbon deposits, which in turn adds to the compression ratio of the engine (which causes preignition if the octane level is insuffecient). The knock sensor should be able to compensate for pre- or late ignition when you switch fuels; if you hear some knocking it isn't necessarily detrimental unless it happens too often.
If you decide to switch fuels, you should use up most of the fuel tank first.

My recent calculations with a 2.0L Volvo 740 shows a slight (decimal) increase in fuel economy (6.1 km/L with midgrade versus 6.3 km/L with premium); albeit the cost per km is still not less than that of regular fuel.