engine knocking when accelerating

[hans_fh]

These days I notice my Yaris Sedan gets engine knocking when the car is accelerating.

My car gets 10,000 miles already and I am using Sam's Club 85 gas. In Utah's Sam's Club, we only have 85 and 91 as options.

I have been using Sam's fuel for two month and just notice this problem these days...

Is there any problem with using 85 fuel in Sam's? Do I need to switch to 91 in Sam's or another gas station?

Thanks a lot!!

[Typer73]

Minimum rating is 87... hence the knock. Try a higher octane.

[hans_fh]

It is really harmful if I kept using 85 for over 7 months? In Utah, most stations have 85 as the lowest option which is called unleaded gas...

[El Jefe]

it's only harmful if it's actually knocking that whole time, but you really should run 87 in it.
do not let it continue to knock unless you want to replace the engine soon.

[hans_fh]

Oh MY GOD!! I DON"T EVEN KNOW THAT I SHOULD USE 87fuel....

WILL CAR BE REALLY DAMAGED BECAUSE I KEPT USING 85 BEFORE??? I WILL SWITCH TO 91 IMMEDIATELY!!! WE ONLY HAVE 85 and 91. HOWEVER, WHEN I GET THE CAR FROM THE DEALERSHIP OCTOBER, THE SALESPERSON TOLD ME JUST USE THE CHEAPEST FUEL.

OH MINE!!!! CAN ANYBODY KILL ME? I AM SO SAD......

WILL THE SITUATION GETS BETTER WHEN I SWITCH TO 91 TOMORROW????

UPDATE:

I JUST CALLED THE SALESPERSON TONIGHT, HE TOLD ME UTAH IS ON HIGHER SEA LEVEL SO THAT 85 IS FINE FOR MOST OF CARS. HE IS BS!!! ANYWAY I WILL SWITCH TO 91 AT CHEVRON TOMORROW.

[slvryaris]

I have never heard of anything under 87 octane, and does anyone know of a car that runs that at minumum other then a Chevy Colt or a Ford Fiesta.

[Capagotks]

in australia, we get 91, 95 and 98. didnt think that it went that low these days...

only use the lower octane for older cars with the smaller compression ratio. the standard it about 9.5-11:1, depending on what car it is (economy-sports respectively)

[Edd]

Capagotks, in Australia we use a RON number. Americans, who love to be different, use (RON+MON)÷2.

Originally Posted by wikipedia

In most countries (including all of Europe and Australia) the "headline" octane that would be shown on the pump is the RON, but in the United States, Canada and some other countries the headline number is the average of the RON and the MON, sometimes called the Anti-Knock Index (AKI), Road Octane Number (RdON), Pump Octane Number (PON), or (R+M)/2. Because of the 8 to 10 point difference noted above, this means that the octane in the United States will be about 4 to 5 points lower than the same fuel elsewhere: 87 octane fuel, the "regular" gasoline in the US and Canada, would be 91-92 in Europe. However most European pumps deliver 95 (RON) as "regular", equivalent to 90-91 US (R+M)/2, and even deliver 98 (RON) or 100 (RON).

Link.

So basically our fuels are the same as the ones in the US. Europe have better fuels than both of us.

[Capagotks]

Originally Posted by Edd

Capagotks, in Australia we use a RON number. Americans, who love to be different, use (RON+MON)÷2.

Link.

So basically our fuels are the same as the ones in the US. Europe have better fuels than both of us.

my bad...

[WRBlue]

Originally Posted by hans_fh

I JUST CALLED THE SALESPERSON TONIGHT, HE TOLD ME UTAH IS ON HIGHER SEA LEVEL SO THAT 85 IS FINE FOR MOST OF CARS. HE IS BS!!! ANYWAY I WILL SWITCH TO 91 AT CHEVRON TOMORROW.

He's right. At higher elevations, an engine needs less octane fuel to prevent knock. It has to do with the lower density. Thats also why you can't compare quartermile times at different elevations.

You're probally getting knock because of the summer heat. Hot air explodes easier than cooler air. Thats why You run richer in the winter and leaner in the summer - but the computer corrects for it. Also thats why carbs need to be retuned every season to run the best.

[JosephDoc]

Yeah, proly use better gas from now on. Take it to dealer if you hear that noise again. Good luck!

[Motorhead6T5]

The car has a knock sensor so your car should be fine. even 87 is questionable with 10.5:1 comp,you will be losing power also from the ecu pulling timing. I've been running 91 and it does feel more powerfull in the midrange.

[Pars]

Originally Posted by WRBlue

He's right. At higher elevations, an engine needs less octane fuel to prevent knock. It has to do with the lower density. Thats also why you can't compare quartermile times at different elevations.

You're probally getting knock because of the summer heat. Hot air explodes easier than cooler air. Thats why You run richer in the winter and leaner in the summer - but the computer corrects for it. Also thats why carbs need to be retuned every season to run the best.

True, I usually run with regulars gas (which is 87 Octane), but if a heat wave is coming, I'll switch to Premium to help the engine run as cool as possible (engine knocking does generate extra heat).

I haven't notice any real advantages with performance (premium vs regular), however on occasion, the engine will feel a little more sluggish then usual, but those isolate occurrence only happen when I'm running on regular gas (probably caused by a bad batch gas, with octane level lower then the required 87).

[churp]

Originally Posted by WRBlue

He's right. At higher elevations, an engine needs less octane fuel to prevent knock. ........

Haven't heard that one before????? Who told you that?????

[swng]

This is just for information and reference (please refer to Post #3849 thereof):
http://townhall-talk.edmunds.com/Web...her%20altitude
I can't judge the validity of all the comments.

Edit: Here is another link:
http://www.bp.com/liveassets/bp_inte..._car_knock.pdf
Middle of Page 2 thereof is relevant.

[churp]

Originally Posted by swng

This is just for information and reference (please refer to Post #3849 thereof):
http://townhall-talk.edmunds.com/Web...her%20altitude
I can't judge the validity of all the comments.

Edit: Here is another link:
http://www.bp.com/liveassets/bp_inte..._car_knock.pdf
Middle of Page 2 thereof is relevant.

Thanks for the reply....I agree with these links, which basically say the thinner air at high altitudes gives the same effect as lowering the compression ratio (which also means less power) in your engine. I wouldn't use 85 octane even in my ex wifes car though.