i desperately needed gas and the closest station only had 93. i usually use 87, but i needed it, so i decided to go with 10$ of 93 until tomorrow where i can find some 87 at a good price.

is it ok to be going back and forth like this? should i wait until the 93 is completely drained?

 

Sure. In fact, some gas stations have just two underground tanks and mix the middle grade in the pump before it goes into your truck. Whether mixing your own petrol cocktail is economical depends on the prices. The cost of 89 is usually halfway between 87 and 91 anyway.

 

ehh...i doubt there is a problem with mixing higher octane with lower...maybe you should just get 93 all the time. that's what i do...i mean its less than a dollar per fill up. put in the extra moola!

 

Just fill with 93. Gas is expensive no matter how you cut it. Its cheaper to throw in the extra $1 a tank than to repair a grenaded engine.

 

but his car does nt call for 91+ it is the 2.4

 

Actually they recommend 91+ for the 2.4 SS. It will run on 87, but you will lose HP.

 

You are losing hp and probably some mileage running the 87 in the 2.4... the manual reccomends 91+ but it's not required. I always filled my 2.4 with premium...

 

You will not hurt the motor by runnign higher octane fuel. In fact higher octane is better because you can run more timing, (in a all out performace mindset). Higher octane fuel is less prone to preignition, and burns slower as well as more completely. Now if you run a tune (reflash, be it HP tuners or some superchip or the like reprogrammer) made for 91 and you run 89 or 87 in there you can and most likely will damage the motor if the ecu persists on ignoring the preignition that will occur. Basically if you run a car that says in the manual it's ok to run 89 then by all means run any fuel you want into it because it's nto going to hurt a thing. But if you have a engine that requires a higher grade try not to run below that grade if you can help it. It can run on the lower grade, that's what's great about these new EFI cars, but be damn sure you don't give it much go peddle while you do.

Now in the other hand, if you are running E-10/E-85 fuel. (Usually midgrade) Then you shoudl do your damndest to keep running it. Its' a different mix of fuel and has ethanol in it, unlike premuim and low grade fuel. E fuels burn differently and thusly your ECU has to learn how to fuel the engine properly for maximum economy and performance. SO switching back and forth between them isnt' the best of ideas. (Case in point Consumer reports ran a flex fuel equanox with Regular 87 and got 16, they then ran a tank of E-85 and got 12, had they let the car run three or so more tanks of E-85 the ECU woudl have learned on it's own how to better use the fuel and used less, boosting economy to probably within a tenth of a mile to the gallon.)

 

cobalts do NOT run on E85. don't use it.

 

all of the pumps around here say "may contain upto 10% ethanol". should i just use premium from now on? will it give me better gas mileage? the manual says i can run 87 fine.

 

The manual says

"... E85 (85% ethanol) and other fuels containing more than 10% ethanol must not be used in vehicles that were not designed for those fuels."

and then

"Your vehicle was not designed for fuel that contains methanol."

sorta looks like the ethanol is okay as long as its not more than 10% ethanol.