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Premium gasoline


we have a Mitsubishi endeavor which says it requires premium gas. what happens if you use regular gas?

Most likely, uneven, uncontrolled fuel detonation would result in damage to pistons and valves. And, this damage would not be covered by the vehicle’s warranty. Do you want to find out the hard way?

If the term used by Mitsubishi was “premium fuel recommended”, you would have some wiggle room, but the meaning of “premium fuel required” is pretty clear.

The key word is REQUIRES. Some cars “recommend” Premium, but yours requires premium.

This means you have a motor with high compression that needs premium so you will not have “pre-ignition” which causes your engine to make a noise called knocking. Pre-ignition and knocking can lead to a hole being burned into one or more pistons which means a very expensive repair job. Your car is also tuned to use high octane fuel for performance.

Cars that recommend premium are fitted with knock sensors that de-tune the motor by retarding the spark timing and thereby avoid the knocking and damage to the pistons. These cars sacrifice some of their high performance potential when run on regular but there is no damage done.

To save a few bucks by using regular or plus you are risking BIG bucks in motor damage repair. Check the manual again REQUIRES means just that. Reommended means you have some flexibility.

Someday you may be stuck somewhere and can only buy regular. Usually there is some premium left in your tank which helps. In these cases be gentle on the motor especially try to reduce “load” by downshifting and keeping the revs up if you encounter steep hills. If you happen to be towing a trailer when this happens buy more premium at the 1st opportunity, because you are operating on very thin ice.

In addition to the possibility of damage that has already been discussed, regular would likely cause reduced power and lower mileage.

Note: on cars that do not require or recommend high test fuel, there will be no gain in power or increased mileage by using high test fuel.

If it says it requires premium you need to use premium or risk engine damage.

However, the Mitsu Endeavor is not a performance model. I understand that manufacturers want to get more power out of smaller engines, but it bothers me that they’d use compression (whether via ratios or boost) that mandate premium. If you were one of those that said “I bought a Mercedes 560SLK…can I use regular?” then I’d seriously question your thinking, but that’s not the case here.

Whrn people as for recommendations for new cars I’ll have to remember to suggest they consider that in their decision. I’m not sure people buying a family car even think of it.

For one thing, you risk voiding the warranty. for another, the expense is minimal compared to the repairs yo might incur by using lower grade gas.

If you drive 15,000 miles per year and get 18 MPG, you will use 833 gallons per year. If the price difference between 87 octane and premium is $0.10 per gallon, then you will pay another $83 each year using premium. If the difference is $0.20, you will pay an extra $167 per year. That’s cheap insurance. Usually mid-grade is 89 octane and premium is 92 or 93 octane. Your owner’s manual should give a minimum octane rating for “premium”.

It should be illegal to put 87 octane gasoline in a car that requires premium. I have an old car that requires premium and I siphon fuel only from cars that are known to require premium. When I obtain gasoline from some cheapskate who has filled an expensive car requiring premium with regular, it really burns me up. If these owners want to ruin their own cars, that’s not my problem. Just don’t make me ruin my car with your bad gasoline.

Maybe I can persuade my congressman to introduce a bill in the legislature to make it illegal not to use premium in cars that require it. If I tell him the reason for this is that I am a crook, the rest of the crooks in the legislature will go along with it.

But I’m sure I’ve heard the Car Talk guys say that it’s not necessary to use premium gas, even on those cars “requiring” it? I’m wanting to buy a Mini Cooper, so this is important to me too!
Is Triedaq joking or not, do you suppose?

I like Ray & Tom Magliozzi, but they would be the first to admit that they have been known to make mistakes with some of their advice. And, this is one instance, at least IMHO.

As to our friend, Triedag, I am confident that he is joshing us.

The Car Guys blew that one.

Most engines today have what’s called a “knock sensor” that senses the shock wave from preignition and retards the ignition timing to try to compensate and prevent pinging. But it isn’t foolproof. It can only compensate within limits. And retarding the timing causes the engine to operate at less than optimum. And if retarding the timing doesn;t completely eliminate the pinging, if the pinging happens only on acceleration and you can’t hear it, it can still damage your engine.

As to our friend, Triedaq, I am confident that he is joshing us.

Just wait until I get locking gas caps outlawed.

I is foolish not to use the fuel recommended.

  • avoid possible damage
  • maintain the performance you paid for
  • maintain the high mileage you like

It varies from car to car, but generally the difference in fuel cost will just about equal the difference in mileage. So why not use the fuel recommended or required?

If you want to buy a fun car and skimp on the fuel to run it, then you should skip over it. Also, if the company wants to be tight about it, they can deny your warrant if they find improper grade of fuel was continually used and caused a problem with the car.
One more thing, the gas tank in the base model Mini is about 10 gallons, so even if 87 is $2.00 and premium is $2.50(maybe an exaggeration, it’s only 20 cents difference where I live), you’re only gonna save $5 if you run the tank dry everytime.