Premium in the minivan.. don't think it likes it.
 

Hi folks,

So due to some weird chance, I ended up with a full tank of premium, 91 octane. I pulled up at the pump on empty and there was a sign on the pump "Out of regular, use premium at same price" and there was a maintenance crew there, looked like they were having some problem with the tanks or something... so I thought, "what the hell, I guess it's getting premium..." and filled up...

Driven a few trips, and the minivan doesn't seem to be liking it much, seem to have lost low end, and need to give it more pedal to get moving. It does sound a little smoother though. Kinda like with acetone, but without the get up and go. It seemed to improve a little the first couple of times I started it, but guess that was all the ECU trim could do and it's still not great. It likes midgrade 89 octane, to the tune of 5% more mileage, but since it's usually more than a 5% cost difference I use 87.

So I'm looking around for something to stick in it to drop the octane, might go with a litre of varsol and a couple of oz of 2 stroke oil. Figure it will probably clean it out while it's at it. Then I guess if it still feels sluggish I'll top it up with 87 when I've run a bit out. I guess I could advance the timing, but that's a PITA, and I'll have to set it back again next tank....

Road Warrior

Strange, our premium is 93...

But I will say this much:
With MOST fuel injected vehicles, the best grade of fuel for it is what the computer was tuned to use... So if for example your van was tuned for 87 octane then that would be the fuel that would likely result in the best performance (and FE).

The only way I know of to get around this is to have the computer re-programmed (to something like a stage-1 chip), neither a cheap nor an easy to do option.

Good luck

It varies by brand here, this one is 91, others are 93 or 94...

Yah okay I see... At least my experience has been with my Dodge which is apparently tuned for 87, any grade but 87 doesn't really do much for the truck... And in some ways much like yourself it almost seems like it hurts (thou I couldn't say for sure but the extra I have to pay at the pump sure don't help LOL).

The one other thing I did notice too thou, you might want to run 3-4 tanks full through it... The benefits of premium aren't always apparent on the first tank, but don't come yelling at me if after 15 tanks it still hasn't improved hehe

I did, I ran more than a few tanks through on my truck...
But in the end I went back to 87, it just wasn't showing me any benefit, none at all.

One way to find out is read your Owner's manual, some tell you what fuel to put in it, that is a fair indicator as to this tuning issue.

maybe its not just the octane. perhaps the station had a problem like water getting into fuel, and thought it was only affecting the regular grade, but maybe it was affecting all their fuels. maybe u got a lil extra water, or random contaminant.

ya cuz octane DOES NOTHING on a low compression engine if you go low enough you could run the car of pretty much anything that burns (hence during the 1930's depression theres story's of people running thier old cars off of moonshine)

The octane ratings are there so if you have a high compression engine (gets more power out of it) sometimes just the heat from the combustion chamber and the amount of compression is enough to actually ignite the mix without a spark plug firing, higher octanes don't ignite when compressed the same amount.

so whats that mean: it means if your car calls for regular then you can use regular- race fuel with no harm or performance drop or gain.

if your car calls for midgrade you can only use midgrade-racefuel cannout use regular because its octane is probably too low.

and obviously if your car calls for premium then you must use premium or race fuel...


so im betting you got water in it or rust particles, etc. BTW next time you see a station that is having repairs to the tanks or pumps DO NOT GO THERE...

Don't think it's got water in because it's not stumbling. I was thinking that 91 had a few thousand less BTU than 87 though.

I agree with 2000mc. If you really are experiencing reduced performance, the gas is defective or contaminated. Under no circumstance should increased octane cause decreased performance/economy.

Your high octane observation may hold true for the acetone yall seem to be testing. Maybe you will need a few tanks before the computer can fully adjust to the acetone?

im not positive, but i also thought that 91 octane had fewer BTU than 87 octane. however, i was thinking that the difference is only a percent or 2, nothing you should be able to feel.

No premium has more BTU. That's why some people see an increase in gas mileage because the engine can get more power out of each stroke. I will get back with more detail soon.:thumbup:

Well I had my morning highway runs today and.......

:(

Drives like I've got it fully loaded with only 20psi in the tires... it kicked down on an uphill merge, seems to be running rich because it smells, and took longer to warm up AND wasn't running as hot on the highway, at about 1/4 gauge instead of 1/3 to 2/5.

I thought it would be quick and easily to google for:
gasoline octane btu
and get the answer, but it's not. Anyway, I'm pretty sure that BTU content doesn't vary by octane rating, except as a result of the gasoline being diluted by whatever was used to raise the octane.

The reason higher octane rated gasoline can produce more power (or, in certain conditions, can produce more mileage) is because it can be used at a higher compression without pre-detonating. That allows the existing BTU content to be extracted more efficiently.

Edit: Simultaneous posts....dude, the gas you got was defective or contaminated, or coincidentally you've had a malfunction. Ask them if anyone else has been complaining about the 91 that they got that day.

Yeah, me too, can find lots of people saying premium has less BTU, but can't find any real figures.

However, I do suspect that this is 10% ethanol, and when I've had 87 octane that I know has had a few percent ethanol in.. it didn't run great.

I'm thinking if it had water in, I should be hearing it stumble more, and I'm thinking if it had particulates in the fuel pump would sound loud (That's usually how I tell how to change the fuel filter)

Agreed though, extra power with high octane in engines designed for it comes from higher thermal efficiency of a higher compression ratio, it's nothing to do with the BTU content of the fuel really. Stock compression ratio of this motor is 8.9:1

Around here, all gasoline of any grade is 10% ethanol. There's a big sticker on the pump proudly proclaiming it...

Could be stale gas? Maybe that station doesn't sell premium very quickly.

What other kinds of contimants or defects could there be?

If there is ethanol in the gas and it happened that it was contaminated with water, the ethanol would allow the water, ethanol, and gasoline to mix evenly. This could prevent the stumbling of water and gas mixes, because the engine isn't getting occasional chugs of water, but a constant stream of a tiny amount.

I've heard the higher octanes also burn slower than the lower in addition to resisting pre-det better. So maybe you are getting an incomplete burn in the lower compression.

Most ,if not all, of the newer preformance engines can adjust for lower octane fuel. They'll put out less power, but my parents seem to be getting EPA with regular in their Acura without trying.

Water is only bad when it's not mixed, ethanol holds very little in solution in gas only a couple of percent, that's where the trouble comes, because it continues to be hygroscopic and draws in moisture. If it was running with a high proportion of water held in solution, I'd expect better performance due to higher cylinder pressure. It's apparently possibly to run 120 proof alcohol in most motors, as long as you drain every last drop of gas first, because it's only when ethanol and gasoline mix there's a water problem.

Do you mean 200 proof? I suspect that the other 40% of volume in most 120 proof alcohols is mostly water...

Ah, I was thinking in the British proof rating and aiming to mean about 70% alcohol by volume, yes, the remaining volume would be water, that'd be 140-150 proof I guess, US rating..... and it will stay in solution unless it's mixed with gasoline or similar, which is where the trouble is. As far as I remember, it goes something like this ethanol 97%, methanol 93% isopropyl 68% for the amount of water if can keep in solution while in solution with gasoline.

Well the numbers is in... see gaslog, doesn't seem to have dinged me... but I was h8ing on it all the way... filled it a little early, but my "canary" station I see off the highway had it's price up, so figured I'd get gas tonight anyway and save $2.

Actually, it did seem to have improved the last two or three trips, since I had to go WOT to merge onto the highway, due to some octogenerian in a cadillac in front of me going 25mph down the on ramp...

Maybe if this premium has those (mythical?) extra detergents it dislodged some flakes of gum which was goobering up an injector until that blew it out.

exactly, higher octane lets you go up in compression thus = more power outa said engine.(hence why race engines use race fuel that is like 105 octane if not more)


i also concour the gas is bad, weiher it be water or dirt

I've never had premium give problems even on my 87 chevy s10. but then I run everything pretty advanced on the ignition.

bad gas gets my vote