: Gas Grades

01-11-03, 11:32 AM
I was wondering what kind of gas you put in your cadillacs. My grandpa has a fleetwood and he heard that if you dont put premium in it it wont run. I doubt thats completely true, but it may suffer performance/ economy problems. Which is the more economical approach? Premium gets better gas mileage, but it costs more. What do you all think

lux hauler
01-11-03, 12:53 PM

6.13 Can higher octane fuels give me more power?

On modern engines with sophisticated engine management systems, the engine can operate efficiently on fuels of a wider range of octane rating, but there remains an optimum octane for the engine under specific driving conditions. Older cars without such systems are more restricted in their choice of fuel, as the engine can not automatically adjust to accommodate lower octane fuel. Because knock is so destructive, owners of older cars must use fuel that will not knock under the most demanding conditions they encounter, and must continue to use that fuel, even if they only occasionally require the octane.

If you are already using the proper octane fuel, you will not obtain more power from higher octane fuels. The engine will be already operating at optimum settings, and a higher octane should have no effect on the management system. Your driveability and fuel economy will remain the same. The higher octane fuel costs more, so you are just throwing money away. If you are already using a fuel with an octane rating slightly below the optimum, then using a higher octane fuel will cause the engine management system to move to the optimum settings, possibly resulting in both increased power and improved fuel economy. You may be able to change octanes between seasons ( reduce octane in winter ) to obtain the most cost-effective fuel without loss of driveability.

Once you have identified the fuel that keeps the engine at optimum settings, there is no advantage in moving to an even higher octane fuel. The manufacturer's recommendation is conservative, so you may be able to carefully reduce the fuel octane. The penalty for getting it badly wrong, and not realising that you have, could be expensive engine damage.

lux hauler
01-11-03, 01:09 PM
Here's another link. It's not a car link but it has some pretty good info.
Click here (http://www.bajajusa.com/Who%20Needs%20High%20Octane%20Fuel.htm)

01-11-03, 01:16 PM
I only used 93 or 94 on my ETC. Even thought the new STS is fine with 87, I'll probably stick to the 93 anyways.. I always get better gas mileage when I do...

01-12-03, 06:19 PM
how are the older engines with 87? Like a 94-96? Or is just worth it to get the high grade?

Allante North *
01-12-03, 08:32 PM
I use 87 octane for casual driving, but switch to 93 when I feel the need for speed. I have never heard any knocks or pings, or gotten any codes when using 87. Many of the other Allante owners use 87, but most go with the recomendation from GM. Premimum Fuel Only. I think the Northstar runs fine on 87, but for best performance I use the 93.

I use 87 only on my Toyota 4Runners, and farm truck and tractor.


01-12-03, 09:06 PM
Is the gas mileage affected at all? Would you get better gas mileage if you just put the premium in? Would the decrease in gas mileage (using 87) offset the cost of putting in 93.

Also, i would like to know what you people use as far as gas additives, if any. Like injector cleaner, etc.

lux hauler
01-12-03, 09:53 PM
Also, i would like to know what you people use as far as gas additives, if any. Like injector cleaner, etc.
In my daily driver ('99 Ford Ranger), I use Lucas (http://www.lucasoil.com/Product_Details.cfm?Product_ID=9) injector cleaner. It seems to do a better job than any of the others that I've used.

01-12-03, 10:23 PM
I only use 89 octane on all cars I have ever own and will most likely use it on the Cadillac too.

01-14-03, 06:11 PM
Is the gas mileage affected at all? Would you get better gas mileage if you just put the premium in? Would the decrease in gas mileage (using 87) offset the cost of putting in 93.

01-14-03, 06:26 PM
I don't think the increase in gas mileage of 93 octane will offset the expense - BUT - I do think it's better for the car. So, instead of a noticable offset, I think there would be a small offset along with cleaner burning fuel..

Someone else chime in here. Maybe we don't have any good gasoline guru's here yet...

01-14-03, 07:27 PM
I suppose ill end up putting in 89- mid grade. Thats what i put, and have put in my GTP, and it seems to be fine.

01-14-03, 07:28 PM
Hey whats the differnet between regular gas and winter gas? Down here we only had this switch for 2 winters so far and not all the brands made the switch.

01-14-03, 07:40 PM
Winter gas is oxygenated - I believe.. I don't know about by you, Wes.. But by me in New York, 89 is a waste.. Here's the price structure:

87 octane $1.50
89 octane $1.85
93 octane $1.90

Can you see the problem here?

01-14-03, 07:43 PM
:shocked2: $1.50 for 87? Damn down here its only $1.35 for 87
$1.41 for 89 and $1.47 for 93.:banana: or maybe its 91 octane not sure but I'll check tomorrow when I fill up my truck.All 37 gallons:mad:

01-14-03, 08:11 PM
OK, i guess i dont really pay attention that much. Here in indiana, its usually about 10c difference between grades. But gas prices change daily. In my GTP, i dont pay for gas, and i am told to put in mid grade. But i suppose its a small price to pay to have a good running car.

01-15-03, 04:39 AM
Yeah, gas is expensive up here in New York.. The problem is, 89 is a waste.. For $1.50, you get 87 octane.. For $1.85 you go up 2 tiny little levels of octane.. For just 5 cents more, you move up 6 octane levels... Is this the way it is everywhere? Or just here in New York.. It seems the gas stations would rather you not use 89...

01-15-03, 03:45 PM
it would save alot of money if they just had regualr and premium. Its really weird, tuesday and wednesday are always the best days to get gas. On the weekend it goes up at least 10c/gal across the board.

It used to be 10c difference, but the companies arent selling the premium, so theyve been lowering the price on premium. I noticed you said the there was a 40c difference between 94 and 87. Thats crazy! Theres never more then 20c difference between them here.

So i guess you either put in regular or premium, cuz mid is a waste. Ive never understood why it goes up 2 octance, and then 4 octane. It still boggles my mind.

I have always heard that you get better mileage from premium, regardless of the Comp. ratio. Is that true? if so, by how much? It wouldnt seem to me that it could be too much, because 6 octane points cant do that much.

I know you may not know this, but do you have to put premium in a GTP. I mean, my parents think its a "high performance" engine, and it only has ~240hp. I know the general rule is if the compression ratio is about 10:1, then you should.

01-15-03, 04:53 PM
I'm no expert but I would put premium in the GTP...

01-19-03, 02:06 PM