octane rating?

I noticed already that a few of you are really insistent on the importance of using premium . You ask often if postees are using it.  I'm not saying it isn't a good idea but with gas sooo high I'm still not sold. Mostly  because i drove our last didco for 6 years on regular and never had a problem with the engine. I sold it with about 165k on it still ran very strong and had all the power of the 98 disco I just bought and am now runnng premium in.
Did any of you actually  get the extra 2mpg you say is possible on premium?
I'm just a car owner with just enough knowledge of engines to be dangerous. I'm curious as to what expertise some of the contributors have. this is not in any way a slam. Just wondering how much some of the free advice is worth.
Always open to new ideas.

I personally haven't done a mileage test with my Disco, but I know in my Cadillac (93 Octane rated) that has a mileage computer, there is a drop in fuel economy by going to regular. I think it was about 2 mpg. Plus it would ping like crazy, no power. When bought my 98 I was driving back from CA. I was initially using regular fuel (didn't have an owners manual at the time) and it was pretty doggy. I switched to Premium pretty quick and there was a noticable improvement in power/performance. I would have to imagine that means a jump in economy too. But I never checked the mileage. The manual on this thing says 90-92 octane, so I wonder what midgrade performance would be like?. 

I noticed a very big difference in power, and yes I got about 2 MPG extra (1.976 to be exact) Its up to you, but running regular causes carbon build up which could be deadly to your engine in the long run. You might have gotten lucky with your other disco, but I wouldn't advise running regular. I don't know if DI's can cope with regular better than DII's or not, and I have a DII so someone else might have to put more emphasis on that. Besides if you really look at how much more you pay with premium, its only about $5-$8, and that might be worth it when you don't have to replace half the parts in your engine.

Thats just my input!
Cameron

wow !
thanks for the scoop on premium. If you say it works I'll stick with it and just assume if you are getting 2more mpg then i will too.

Your 98 could handle a lower octane gas, it would get less mileage and actually they were know for severe carbon issues which was know to bend exhaust valves.
Bottom line it will cost you more in the long run if you run a lesser octane, and yes I have been in areas where while on the road I couldn't find supreme and ran on a lower octane, my mileage and power did suffer.

The owners manual says to use premium. Who knows better than the people who built the engine?
Using the $.10 spred which is common here in West MI. And buying 20 gal of gas...
$3.00=$60 (87 octane)
$3.10=$62 (89 octane)
$3.20=$64 (93 octane)
It is only $4.00 more for a tank of gas and when you get 2-4 mpg more you recupe your money and then some.
More power, better mpg and longer engine life. You can pay alittle now or alot later.

and premium is still less than diesel

Yes but coming from europe and the UK I can assure you that you get much better mileage from Diesel, I ran a 1995  Range rover and always returned 25 + but do prefer the petrol..............or did before gas prices climbed. We need to pressurize LR to give us the option, when I left the UK the diesel unit being used was a 5 cylinder BMW and it was so clean no catalyst was needed. Be assured LR USA are using mushroom management, keeping you in the dark and feeding you bull s..t. PS the diesel was also very quiet

True.

I don't know why any company would want to limit their sales.
If LR would bring all their line here (N.A.) I think LR would not be
up for sale yet again.

Well.... It does appear that  If the U.S. auto manufacturers finaly get it together and start offering small block deisel powered cars , the cost of diesel will be so high that it won't help the average driver save a buck. I noticed last week that diesel at our local cheapest gas station was 44 cents higher than reg.-  Whats up with that ? I can remember(just barely) when I started driving 40 years ago, reg gas was right around 23cents / gal at that time diesel was 10 cents! Les than half the cost of reg.! Its true!
Anyhow... I would love to find a way to have a nice 4 or 5 cylinder diesel in a disco even if I have to give up some power. I've looked into conversions. The disco is so nice to drive if we could just get some mileage.

I have read that by using lower octane fuel, your engine's cpu will detune and produce less horse power and lower your miles per gallon. It would be great if midgrade was 91 since premium is 93 at most stations around my area. True the difference is only a few dollars per tank, however in some places the credit card companys limit your amount you can spend....... 

Flame suit on.
 
I have only had my 98 Disco for about 6 months. With 87 octane I get
15.7 mpg consistently. I just ran  5 tanks of 91 octane and
had a best of 15.1 and averaged 14.6 mpg. I can tell no difference in
performance.
 
I wanted to run the comparison before I installed my new 8mm wires and
plugs.
 
Mike

Octane is a measure of gasoline's volatility. Higher octane means it is more stable, combusts best at higher compression, and is less prone to premature detonation under pressure (pinging), all things being equal. Your engine is designed to operate most effeciently at a specific octane level (determined primarily by its compression ratio), so in general you should always use what the manual calls for. Conversely, using high octane fuel in engines designed for lower octanes can create drivability problems associated with incomplete combustion because the engine creates less pressure than the fuel requires. Of course, some newer vehicles are engineered with knock sensors and can actively adjust the timing to compensate for reduced octane. In those vehicles in some cases, it is permissable to use a lower octane as stipulted in the owners manual, however, generally perrformance is sacrificed. Also note that octane rating at the pump is an average of two different methods of determing octane. One is research octane, and the other is motor octane. If you look for it, the next time you're pumping gas, you'll notice R+M/2 on the octane rating sticker. This means it is possible that two different gasolines with the same octane rating, may have significantly different research and motor octane measurements, and can perform differently in your vehicle. Unfortunately, the majority of the damaging pinging that occurs is inaudible, so choose your source wisely, and pay attention to how your vehicle feels and sounds under load and during acceleration to prevent carbon build up and premature failure.

whew! you said a mouthful Jigray3! Sounds like you know what you're talking about. How do you figure Sooners gets worse mileage on the higher octane?
Oh well. I'l run the mileage tests on my 98 and see how I do.

My book says 90-92 Octane. That's Mid-grade in some areas, isn't it? Premium is 93 Octane in our area. So, theoretically, mid grade, which is cheaper than Premium should work just fine, right?
 
Mark G

quote:

ORIGINAL: Sooners

Flame suit on.

I have only had my 98 Disco for about 6 months. With 87 octane I get
15.7 mpg consistently. I just ran  5 tanks of 91 octane and
had a best of 15.1 and averaged 14.6 mpg. I can tell no difference in
performance.

I wanted to run the comparison before I installed my new 8mm wires and
plugs.

Mike

LOL! You need the flame suit. This is one tough room to convince using the lower oct. brew
 
Having said that, right now I am running my own test using 91 oct. (highest I can find here in So.Cal)
 

quote:

ORIGINAL: b c

Well.... It does appear that  If the U.S. auto manufacturers finaly get it together and start offering small block deisel powered cars , the cost of diesel will be so high that it won't help the average driver save a buck. I noticed last week that diesel at our local cheapest gas station was 44 cents higher than reg.-  Whats up with that ? I can remember(just barely) when I started driving 40 years ago, reg gas was right around 23cents / gal at that time diesel was 10 cents! Les than half the cost of reg.! Its true!
Anyhow... I would love to find a way to have a nice 4 or 5 cylinder diesel in a disco even if I have to give up some power. I've looked into conversions. The disco is so nice to drive if we could just get some mileage.

Keep in mind diesel engines were originally designed to run on peanut oil.  The advantage of  a diesel is the option to be 60% petroleum free during the winter, and 100% petroleum free during warmer months (depending on your local climate). 

If you're not aware of how this is a national security concern and the fact it has not been made a top priority by various North American governments you'll need to catch up a bit.  The other major advantage is a significant reduction in toxic emissions, about 95-99% depending on the toxin when switching off petroleum based fuels.

This is why not having diesel engines available is so infuriating, it removes the option of not contributing to the above issues. 

quote:

ORIGINAL: jigray3

Octane is a measure of gasoline's volatility. Higher octane means it is more stable, combusts best at higher compression, and is less prone to premature detonation under pressure (pinging), all things being equal. Your engine is designed to operate most effeciently at a specific octane level (determined primarily by its compression ratio), so in general you should always use what the manual calls for. Conversely, using high octane fuel in engines designed for lower octanes can create drivability problems associated with incomplete combustion because the engine creates less pressure than the fuel requires. Of course, some newer vehicles are engineered with knock sensors and can actively adjust the timing to compensate for reduced octane. In those vehicles in some cases, it is permissable to use a lower octane as stipulted in the owners manual, however, generally perrformance is sacrificed. Also note that octane rating at the pump is an average of two different methods of determing octane. One is research octane, and the other is motor octane. If you look for it, the next time you're pumping gas, you'll notice R+M/2 on the octane rating sticker. This means it is possible that two different gasolines with the same octane rating, may have significantly different research and motor octane measurements, and can perform differently in your vehicle. Unfortunately, the majority of the damaging pinging that occurs is inaudible, so choose your source wisely, and pay attention to how your vehicle feels and sounds under load and during acceleration to prevent carbon build up and premature failure.

 
 
Well said.
If you are getting the same mpg on lower octane are you sure
that its not the same fuel.
Some people will sell 87 as 92 and most people will never
know.
Always use a national brand as they have oversight on whats in the tanks.
You can use what you want or use what your LR calls for.

quote:

ORIGINAL: b c

whew! you said a mouthful Jigray3! Sounds like you know what you're talking about. How do you figure Sooners gets worse mileage on the higher octane?
Oh well. I'l run the mileage tests on my 98 and see how I do.

He is taking advantage of the the lower octane fuel's higher volatility, getting a bit of a free ride, but this works both ways. The higher volatility (lower octane) fuel in a high compression engine means the fuel begins to combust on its own under load, or in the presence of heated deposits, or simply due to residual heat from a spark plug before the piston reaches the top of its stroke. This means the piston is trying to compress the explosion already occurring in the cylinder. If you want to kill an engine prematurely, this will do it.

I hate it when people know more than me.Sounds like you've done your homework on this stuff.thanks