SUV Requires Premium Unleaded

I have a 2004 Mitsubishi Endeavor AWD that has about 54k miles. This vehicle, per manufacturers recommendation, requires premium unleaded. When I have tried regular unleaded, the engine knocks horribly. Otherwise, this is probably one of the best vehicles we have owned, but the premium is getting expensive. Is there any way to use regular fuel without causeing performance issues.

If it knocks, then no. Unless you decide to move to Denver or some other high altitude city.

What does high altitude have to do with quality of gasoline used?

At 7,000 feet, some carbureted cars used to sputter a lot because of the lack of oxygen as well as the lack of atmospheric pressure. Thin air. You won’t run as well either. The regular won’t burn as fast, so it performs like higher octane fuel.

Knocking horribly is the engine’s way of telling you that it doesn’t like that fuel and could well be damaged if you insist on putting that in the tank. Any money saved at the pump will likely be lost by the reduction in gas mileage, not to mention the potential repair costs. In the end, it could end up costing you more money than simply using what the engine requires.

Honestly, if you don’t want to pay for what the engine needs, you shouldn’t have purchased a vehicle that needs it. Assuming the manual states that premium is required, that is what you have to use or else the engine will be damaged. And it won’t be covered under warranty.

What does high altitude have to do with quality of gasoline used?

Repeat after me… Octane is NOT a measure of quality. Again Octane is NOT a measure of quality. It is also not a measure of energy. It is a measure of how fast the fuel burns. Higher octane burns slower so it does not knock and damage the engine as well as loose power.

At higher altitudes the reduced air pressure reduces the speed of burning/total pressure so it is not as big a problem.

 [b] premium is getting expensive. [/b] 

True, but then regular might even cost you more. You will get less mileage using regular and it may be enough that the total cost is more than paying for premium. You will also loose power and damage you engine. Retarding the spark somehow or reducing the compression is only going to result in less mileage.


Thanks to all and appreciate your answers.

premium is getting expensive

I’ve personally torn into an engine that a guy blew up his engine by knocking. Two pistons were complete destroyed…along with a cylinder wall. Couldn’t even rebuild the engine…had to get one from a junk yard. Yup Premium is getting expensive…but rebuilding an engine or plopping in a new or used one is far more expensive.

PREMIUM fuel vs regular is getting cheaper as price of gallon gets more expensive.

The price difference of premium vs regular remains the same as when fuel was $1, $2 then $3 and now $4 per gallon. Usually premium is $0.20-$0.25 more per gallon. So fuel prices have risen but the cost increase lessened to something like 6-7% more.

So your cost difference of using regular vs premium has not changed, just the overall fuel bill.

I remember the late 1980’s putting premium in $1.20 into my Saab 900 turbo. That price was a 20% increase in price for premium vs the $1.00/gallon for regular fuel.

That’s true but you’ll find that in those areas, the octane ratings are reduced to match. Fer instance, at sea level you may find 87, 89 and 91 octance ratings whereas at altitude, the ratings are 85, 87 and 89. “Premium” is premium no matter where you live and the cost difference is consistent as well.