Fuel 85 or 87

S

sutherlandjl

Member
:
2002 ES, Black
Ok...I live in Colorado Springs, CO. I have a 2004 6i. I have been running Mid Grade (87 here) in the car but someone told me that since we are at a higher elevation (6035ft) it was ok to run the lower octane (85). Anyone know anything about this? Running the lower octane would really help me out a lot. I drive 60 miles round trip to work 5 days a week. The gas bill is killing me. -Jesse
 
Getting2knowMaz said:
I'm almost on sea level and run 91 or 93 octane.
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Well I have lived at sea level and know that 87 is fine there. But here the air is a lot thinner. It may or may not make a difference.
 
These cars are tuned and calibrated to work with 87 octane, you must only use 87 octane. 91 and 93 octane does not have any benefits to the engine, it will just deteriate faster.
 
91/93 octane = bad...unless your driving an atenza.

I would stick with 87 octane as per manufacturers recommendations unless the car is modified in such a way which requires additional octane gas.

Situations where this would occur...

1) Track day. (Car's going to be running extremely hot, so a little extra elbow room against pinging is a good idea)
2) An intake which leans out the air fuel mixture enough to cause pinging.
3) A unichip or reflashed ecu which is tuned for 91/93/94 octane.

Remember octane is only a POTENTIAL for power. Higher numbers do not result in more power, cleaner engines, or better mileage unless the car is capable of adapting to the higher octane. The 6 can't, and thus the exact opposite occurs. You lose a slight amount of power, your mileage gets squewed, and you increase the amount of combustion deposits due to unburnt fuel.
 
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I am not worried about not getting enough power from the fuel choice. I hate the price. I want to put the 85 octane in it. But i don't want to hurt the engine. But I was told 85 was ok here at this elevation. I just need to know if it is.
 
car can read 85 octane...it will then pull timing and spark to prevent engine wear fron inadiquate octane level. VVT will fall off horribly if you leave the 87-89 octane range on a non tuned 6. 85 will burn faster than 87 and in turn will kill MPG if thats the reason for the switch from 87 to 85.
 
89 actualy won't give you a better anything over 87 unless the gas is falsely marked or not even at that octane rating. some non turbed 91 and up octane gas cars can "be comfortable" on 89 from a few "unaproved" sources. Dodge Neon R/T-ACR is one of those 91 octane cars.
 
Mikey444 said:
it will just deteriate faster.
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What?!?

crossbow said:
91/93 octane = bad
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Other than cost, how exactly is that bad?

There is nothing wrong with running higher octane. You won't get anything out of it necessarily, but it's not harmful in any way.

As far as running 85, you may be ok. But it's not O2 level that determines octane rating. Compression, heat and other things are factors. 85 has a lower flash point than 87 (albeit just a little). The heat from compression may be enough to set it off depending on conditions so you may have some random cases of preignition in which case your timing will back off to compensate.
 
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Take a 9.7:1 fuel ratio @ 87 octane, then up it to 93.

Watch as the deposits build up, and your engine wear numbers spike up due to excessive fuel dilution caused by unburnt fuel.
http://www.bobistheoilguy.com
Search for UOA's and Fuel Dilution.

Normally in a car that wasn't so pig rich, it wouldn't be so negative. But in the 6 its downright dangerous...especially considering how much it costs to replace those precats which are integrated into the exhaust manifolds.

I mean its your car, but honestly you can just imagine whats happening with 93 octane in a car thats at 10:1 A/F 1000 rev's before redline.

stockaf.jpg
 
-5.5 fill ups/ month
-about 16 gallons/ fill up
-$2.27/ gallon...$199.76/ month...premium
-$2.17/ gallon...$192.50/ month...mid grade
-$2.05/ gallon...$182.16/ month...regular
-$124.08/ year = savings/ year - If I switch from Mid Grade to Regular

These are the figure I am coming out with...plus we have a Dodge Dakota that has a 5.9L in it. But the wife drives it and only drives it about 20-25 miles a day. So you can see why I am concerned.
 
93 takes longer to burn than 87. Think of it as each explosion forces the pistons down. If the gas doesn't completely burn then how much energy is gonna be transfered apon explosion? Unburnt fuel washes the cylinder and goes into the cat. Remember V6 owners that the 87 is already being dumped into the cats so dumping 93 is even worse. If you kill the precats they in turn may kill the engine. Will it hapen right away?...Maybe not. Over time?...Do you wanna risk it ;) also as pointed out above there is a savings just on pumping the 87 over 91. The only thing not included in that savings is the MPG of a 6 with 87 and a 6 with 91. that would make the savings even higher since the MPG will suck with 91.
 
Well over the next month I plan to do a little study with our 3 levels of octane just to see what kind of MPG I get with normal driving. I will keep everyone posted.

Jesse
 
Octane studys should be done on a month by month basis. Weekly comparisons don't offer enough datapoints.

Compare one month to another, and you start eliminating the usually variables. A 4 mpg variance between fillups is still considered normal variance. It doesn't take too much to get a 4 mpg drop or gain in any car. But when you compare the monthly group of fillups (average for the whole month) to another month, you can appreciate the differences more readily.
 
keep all reciepts and zero out the trip odo as well ;)
 
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