What grade of gas do you typoically use and why? I am seeing all different opinions on the internet. How do I know what grade of gas my car calls for?
grades of gas
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homebrewz
Minister of Fire
87 Octane, because my vehicles don't require anything greater. Look in your owners manual for the lowest octane fuel you can use.
The only time you really need to switch to a higher octane fuel is if you are getting pre-detonation, usually heard as a pinging or
knocking sound, usually while going up hills. A higher octane fuel will have a higher combustion temperature and will help with this.
A local saw shop told me to use the highest octane fuel for my saw because it breaks down slower, for those times when you're not
cutting that much, and the fuel just sits around.
The only time you really need to switch to a higher octane fuel is if you are getting pre-detonation, usually heard as a pinging or
knocking sound, usually while going up hills. A higher octane fuel will have a higher combustion temperature and will help with this.
A local saw shop told me to use the highest octane fuel for my saw because it breaks down slower, for those times when you're not
cutting that much, and the fuel just sits around.
A fuels octane rating is its resistance to burn, basically. thats why higher octane fuel resists detonation, lower volitility, therefore more control on the burn rate. use what fuel your owners manual states to use.
chrisasst said:
What vehicle do you drive? Sports cars usually require high octane fuel which allows greater compression.
Highbeam
Minister of Fire
PINEBURNER said:
That's right. High octane fuel actually burns slower.
In my vehicles I use the lowest octane that the manual allows since it is the cheapest. I have no issues with sludge, water, pinging, or other often warned about fuel issues. Maybe back in the day vehicles with their emissions junk were more sensitive but modern auto engines can eat a very varied diet of fuel and run great the whole time.
A car that requires a high octane fuel is a car that the engineers screwed up on or one where they wanted to get a few more HP by upping the compression ratio as a cheap way to beat the competition at the expense of the car's future owner.
There is nothing magical about high octane fuel other than the octane rating.
webbie
Seasoned Moderator
I have a new Passat 2.0 Turbo.
It calls for higher octane - and owners have reported better MPG with high grades. They claim you are fooling yourself by using too low of a grade with this engine.
However, in my ultimate lack of wisdom, I am using mid-grade..around 90.
My excuse is this - I am very light on the gas and it is my understanding that the higher octane is more important when one is using the turbo on a more consistent basis. I suppose I will find out sooner or later if the MPG claim is correct. Right now it gets about 29 on the highway....still fairly new, though.
It calls for higher octane - and owners have reported better MPG with high grades. They claim you are fooling yourself by using too low of a grade with this engine.
However, in my ultimate lack of wisdom, I am using mid-grade..around 90.
My excuse is this - I am very light on the gas and it is my understanding that the higher octane is more important when one is using the turbo on a more consistent basis. I suppose I will find out sooner or later if the MPG claim is correct. Right now it gets about 29 on the highway....still fairly new, though.
Deere10
New Member
Autos will say in the owners manual. Most cars will be ok on 87 octane. My husky saw wants super the 92 or 93 octane. I wonder what the blocks per tank break down to in the saw as to mpg in a car???
Highbeam
Minister of Fire
Well a 50 cc saw compares pretty well to a 2000 cc car engine. That's 400 times the displacement. Or compared to to the 7300 cc engine in my ford pickup it would be like 1460 little chainsaw engines running along.
The turbo'd gas engine has a low compression when not under boost that won't need much octane at all. In fact a lower octane requirement than normal engines. When under boost and being crammed with fuel and air the compression ratio goes way up and demands the high octane to prevent preignition or pinging which will sound like a few pieces of pea gravel being shaken violenty in a pop can. Enough preignition in a modern car will cause the SES light to go on since the condition spews tons of unburnt fuel into the atmosphere.
They "could" design a turbo engine that doesn't require premium fuel but they can squeeze even more power out of it if they require premium and HP sells cars.
The turbo'd gas engine has a low compression when not under boost that won't need much octane at all. In fact a lower octane requirement than normal engines. When under boost and being crammed with fuel and air the compression ratio goes way up and demands the high octane to prevent preignition or pinging which will sound like a few pieces of pea gravel being shaken violenty in a pop can. Enough preignition in a modern car will cause the SES light to go on since the condition spews tons of unburnt fuel into the atmosphere.
They "could" design a turbo engine that doesn't require premium fuel but they can squeeze even more power out of it if they require premium and HP sells cars.
I have a 2000 pontiac montana. Just got it last week. It is getting exceptional gas mileage right now. I would like to keep it that way. I don't have a manual.
Gooserider
Mod Emeritus
chrisasst said:
Might be able to find it on line - check to see if it's available on the Government Motors website, or possibly look for an "enthusiast" site...
Gooserider
jabush
Feeling the Heat
chrisasst said:
If it's the 3800 v6 then all it needs is 87.
If it's the 3800 supercharged, then it calls for 91 octane. My wife's Pontiac Grand Prix has the 3800 supercharged engine in it. Damn thing is an absolute smile maker so I have no problems paying for the better fuel.
I keep track of the fuel mileage in every vehicle I own, at every fill up. In her car, I find that with NORMAL fuel (no ethanol) 87 octane definitely reduces fuel mileage (as much as 2mpg) and the car definitely feels like it's timing is being retarded. However, I notice no diference between mid grade (89 octane) and high test (92 octane).
When it comes to filling that car up with fuel that is 10% ethanol, I get about a 2.5 mpg drop unless I use the highest test available. Then I still come in about 1mpg under the norm for non-ethanol fuels.
Other factors can be winter versus summer blend fuels. I can get the log book out of my chevy colorado and tell you the week that they switch fuel blends from summer to winter since 2005 in my part of the state. Reason I can tell is I instantly lose 2 mpg, regardless of what the weather is. For some reason, the truck prefers the summer blend fuels with more anti-smog additives in it. For that truck too, it's fuel mileage is not dependent upon grade. I've tried all grades in all seasons and that truck just doesn't care. Ethanol blends drop the truck's mileage about 1.5mpg.
In my 96 F-150, so long as I keep it full with something better than water, it just plain doesn't care.
So, at the end of my long post, I suggest that you do the same as I have (if you really are an ultimate nerd who just MUST know) and keep a log for a while. In about a year or so, you'll be able to make an educated assessment of your vehicles fuel demands.
pen
I'm fortunate, I have two gas stations that sell ethanol free fuel. I try to run that in my saws, etc; when I can. Usually premium. Best thing I've ever used as a fuel additive is "Sea Foam". Have had fuel sit in a string trimmer all winter, come summer, shook up the tank, and it started right up and ran fine. I've never had a carb or fuel problem with anything , thats had seafoam in . Even running the ethanol fuels. And I've been using seafoam for the last 10 years. Good stuff
mayhem
Minister of Fire
According to Edmunds, the only engine in the 2000 Montana was the 3.4 liter v-6. Regualr 87 gas is just fine.
I second the seafoam treatment. Use it as recommended and it'll help keep your fuel, combustion and air intake systems operating properly. Well worth the $9 a can.
This gets the idea across, but I don't think its really correct. A fuel's octane rating is really just a measure of that fuel's resistance to heat-ignition...basically raises the flash point of the fuel. I think you know that, I'm just being anal about the workding. Sorry, can't help it.
I second the seafoam treatment. Use it as recommended and it'll help keep your fuel, combustion and air intake systems operating properly. Well worth the $9 a can.
This gets the idea across, but I don't think its really correct. A fuel's octane rating is really just a measure of that fuel's resistance to heat-ignition...basically raises the flash point of the fuel. I think you know that, I'm just being anal about the workding. Sorry, can't help it.
jharkin
Minister of Fire
Webmaster said:
If you are light enough on the gas to stay off the boost then yes you probably can safely get away with the lower octane. Being on boost has the same effect generally speaking of running higher compression and thus requiring higher octane. (Which is why turbo motors often run lower base compression ratios than their NA coutnerparts - more headroom for boost)
On most all modern cars that require high octane, you can usually get away with running lower octane. The ECU typically has a knock sensor that will detect the onset of pre-ignition and retard the ignition timing to compensate. In turbo motors the ECU can often limit boost as well to compensate for lower octane. The downside is that your gas mileage is reduced and wear and tear on the engine is increased so you are not saving as much as you think.
My car calls for 91 (11-1 compression ratio). The owners manual states something like "if 91 octane or greater is not available, 87 may be used temporarily but performance and gas mileage will be somewhat reduced"
Later
New Member
- Jan 30, 2009
- 456
The computer systems on newer cars monitor for detonation and retard the timing to prevent it. Many times you'll see a drop in mileage when switching to a lower octane fuel - caused by the retarded timing.
I should read the posts better - sorry for the duplicate information.
I should read the posts better - sorry for the duplicate information.
jharkin
Minister of Fire
Highbeam said:
But what would be the point? The reason for turbos, high compression ratios, and high RPMs is to get more power out of smaller displacement. This increases your efficiency as the engine is lighter and more compact so you are using less fuel just to move the weight of the engine. When the engine is lighter the vehicle size and structure can also be smaller and lighter, compounding the savnings. In addition, for a lot of reasons, gasoline engines are much more efficient when working hard under load than when loafing along just above idle (reduced pumping losses etc).
Its true that HP sells cars, but that is not the sole reason for high compressions and premium fuel. Car makers could easily just put the same old big iron in and save the considerable cost of R&D for new engine designs if it was only about the power.....
berlin
New Member
Hi octane fuel is only necessary if your vehicle requires it. Lower octane fuel actually contains more energy per gallon and on vehicles that allow it's use will actually give you better mileage and performance. If your vehicle requires higher octane- use it. On modern higher compression vehicles that require higher octane fuel using a lower octane fuel may actually give you lower mpg and likely won't knock. This is because all modern cars- esp. higher performance/boosted engines have knock sensors that will will retard timing/change air/fuel ratio to prevent pre-detonation. On vehicles with turbos/supercharges it can also change when your wastegate opens and reduce max boost. In short, if your car requires it, use it, if not don't; doing the reverse in either case will cause a decrease in performance and fuel economy.
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