Cadillac Owners Forum banner

1 - 20 of 43 Posts

·
Registered
Joined
·
12 Posts
Discussion Starter #1
I don't know how many of you have noticed this but the Premium gas in most parts of Texas has a very low octane rating usually 90. A mechanic once told me it was a waste of $$$ buying premium gas. He instead told me to use regular gas with octane booster addictive. Obviously I did not follow his shallow advice but it had me thinking. Why can't I use Super instead of Premium gas since the difference in octane rating between the two is almost insignificant.
Another question has anybody used Z-max (Oil Addictive)on their 4.9L and does it hurt to use it.??
 

·
Registered
2005 CTS-V, 1994 Infiniti Q45
Joined
·
7,658 Posts
PREMIUM!!!!!!!!!

You didnt buy a cadillac to be cheapened by cheap gas! And the additives add virtually nothing. Besides, premium is only 10-15c more expensive, and by buying 20 gallons you save 2-2.50. A bottle of octane boost may cost 5.
 

·
Registered
White Diamond 2001 STS
Joined
·
1,317 Posts
The octane rating in the southwest states is lower because it can be. Engines are less prone to knocking in dry air, and the octane rating is lower because of it. Octane is an anti-knock additive that is simply added to gasoline (to my understanding). In other words, a 93 octane rating in Florida is comparable to 90 octane in New Mexico, because of the differences in climate.

On the pre-2000 Northstar engines, the system is tuned for maximum power on premiun fuel. Premium fuel is recommended for these vehicles. You can run a cheaper grade of gasoline, and the knock sensor will notice any knocking as a result of it, and retard the ignition timing appropriately. You shouldn't be able to measure more than a 5hp or so decrease I wouldn't think, because of the retarded timing.

I'm surprised at the mechanic's recommendation for octane booster. It's full of MTBE that will coat your spark plugs and exhaust stream with a red coating that may damage/foul these devices. I wouldn't use any fuel additive in my Cadillac! Modern fuels are very capable of keeping the fuel system clean and free.
 

·
Watching the Watchers
Joined
·
5,959 Posts
jadcock said:
Octane is an anti-knock additive that is simply added to gasoline (to my understanding).
I dont beleive octane is a substance at all, it is a rating, and is derived using an eqaution. Much like farenheit is a rating not an actual THING. To my understanding the higher the octane rating the slower the burn rate of the fuel, thus a cooler burn, that does not promote knock as easily. I'm no expert here so i would be open to further explanation
 

·
Registered
1984 Fleetwood Brougham coupe
Joined
·
1,576 Posts
Originally posted by Qristofer
I don't know how many of you have noticed this but the Premium gas in most parts of Texas has a very low octane rating usually 90.
Most of Texas? I been to Austin Dallas and live in San Antonio and all the grades of gas that I have seen are 87,89,93.
 

·
Registered
'05 Expedition
Joined
·
7,651 Posts
I thought that the newest Northstars used regular unleaded? Can anyone clarify this for me?

I usually run 93 octane in my 4-cyl prelude. They recommend "high octane" fuel, but don't specify a number. A few weeks ago I ran 89 octane just to see what would happen. When I got down to about 1/2 tank, it started knocking under moderate acceleration. The problem gradually worsened. I ran the tank completely empty and filled up with 93 octane.

It CONTINUED to knock. Finally, after I had used about 1/4 tank, I figured out that I needed to re-set the ECU (computer). Problem solved. It probably would've cleared itself up with or without the re-set, I just speeded up the process by doing it manually.
 

·
Registered
White Diamond 2001 STS
Joined
·
1,317 Posts
Elvis said:
I thought that the newest Northstars used regular unleaded? Can anyone clarify this for me?
Yes. 2000 and later engines recommend regular unleaded, 87. There should be no advantage to using premium with these engines, since performance is already optimized for 87. It won't "advance" the timing or anything if you run high test. It has no way of knowing you're running high test because it won't knock on low test. :p
 

·
Registered
Joined
·
3,683 Posts
jadcock said:
Yes. 2000 and later engines recommend regular unleaded, 87. There should be no advantage to using premium with these engines, since performance is already optimized for 87. It won't "advance" the timing or anything if you run high test. It has no way of knowing you're running high test because it won't knock on low test. :p
IRC, new north* has little bit lower compression ratio and computer tuned to accept regular but premium is still recommended. Whereas pre-2k is required to put premium gas.
 

·
Registered
White Diamond 2001 STS
Joined
·
1,317 Posts
Devil_concours said:
IRC, new north* has little bit lower compression ratio and computer tuned to accept regular but premium is still recommended. Whereas pre-2k is required to put premium gas.
The newer engine has a 10.0:1 ratio versus the old engine's 10.3:1. It also has vastly redesigned "fast burn" combustion chambers. 87 is recommended for these.

1993-1995 engines technically were "premium required". After a length of time (I guess those two years), they decided that they'd accept regular fuel and it'd provide adequate performance for most climates, they officially changed it in 1996 to "premium recommended". The fuel gauge still says "premium required", but the engine runs fine on 87. I've ran mine on 87 many times. I really can't tell the difference in performance.
 

·
Banned
Cadillac
Joined
·
16,105 Posts
Before I got the '91 Fleetwood 4.9 from my dad, it was knocking badly. I am happy there was no engine damage 'cause the car recommends premium! He didn't like to buy premium because it was close to a dollar a litre. Needless to say I will always use premium with this car. Question: I thought there was a power advantage to running prem. , and also doesn't it burn "cooler" or something, because they describe detonation as two flame-fronts colliding with each other which can cause spark plug or engine damage? The '91 was definetely "premium required" and I would be interested to find out if anyone ever had engine damage from using regular instead of premium.
 

·
Registered
2001 DHS, 1996 DeVille, 1993 Deville, 1989 Seville
Joined
·
46 Posts
I started to use reg 87 in my 93 (4.9) when the gas prices went through the roof a few years back, and I haven't noticed any problems, ie; knocking or pinging. The car still runs smooth, and the mileage is still average 20 mpg. I haven't had the courage to try this with my NS, I just don't drive it as often. (Premium is still over $2.00 in Phoenix!!!!)
 

·
Registered
Joined
·
6,471 Posts
Elvis said:
I thought that the newest Northstars used regular unleaded? Can anyone clarify this for me?

I usually run 93 octane in my 4-cyl prelude. They recommend "high octane" fuel, but don't specify a number. A few weeks ago I ran 89 octane just to see what would happen. When I got down to about 1/2 tank, it started knocking under moderate acceleration. The problem gradually worsened. I ran the tank completely empty and filled up with 93 octane.

It CONTINUED to knock. Finally, after I had used about 1/4 tank, I figured out that I needed to re-set the ECU (computer). Problem solved. It probably would've cleared itself up with or without the re-set, I just speeded up the process by doing it manually.
You're absolutely correct.
 

·
Registered
Joined
·
6,471 Posts
This is the way it works guys:
The original Northstars were determined to require premium. After a couple years, Cadillac distributed an internal memo (which of course I recieved) that indicated that the Northstar could in fact handle lower grades of fuel. In the memo, they stated that the only problem that would be encountered would be slightly lower MPG and 0-60 times. They even included the test results in the memo. Unfortunately, a couple weeks after the issuance of the memo, I sent a memo to Cadillac engineering stating that after a short time on mid-grade fuel (90 octane) our fleet cars had all experienced an engine knock that we had traced to a "carbon-knock" caused by heavy carbon deposits. A dose of top-engine-cleaner had cured the knock but I felt that the engines had undergone an unusual amount of wear due to the knocking prior to the top-engine-cleaner. Immediately, Cadillac issued another memo stating that the Northstar should use only "premium".

Unfortunately, due to factors such as "Octane Distribution" etc., the ACTUAL octane found in any car, at any given time may vary quite a bit. As you may know, the engine management system can compensate for "some degree" of octane variation by retarding ignition timing. Again unfortunately, by the time the computer "senses" the need to retard timing, there has already been some degree of engine knock occuring. Plus once the timing is decreased, the engine performance and MPG will suffer proportionately to the amount of "compensation" the management system initiates.
Due to the vast variation in "actual" octane at any pump, at anytime, and the variation in condition of anyone's engine and/or management system, I always recommend using AT LEAST the recommended octane in their car.
Perfect example would be me and my car. The recommendation is for regular but I ALWAYS run premium. It's just a cheap insurance policy to me.
Oh, and BTW, octane boosters are far from cost a effective way to "routinely" raise the octane in your fuel.
 

·
Registered
Joined
·
55 Posts
just one thing to say!
I know this for a fact, octain booster (MAY) increase the octain rating of gasoline, it also may not. Depends on the refining process on if you get a real 87 octain or a batch that reached 87 in one sample. The 93 octain rating of most premium gas is accurate. Thats why its more expensive. Another thing to consider is this. If you buy your gas from JOE BOBS country store you dont know what your getting or where its comming from. Most of the time its from the LOWEST BIDDER in turn equals more deposits and less additives. BUY from companys that have shown they dont cheat the consumer with thier gas. EXXON-MOBIL, CHEVRON, CITGO, ect ect. You wont be sorry. I've already had problems with the whole gas thing, trust me 700 for something I could have avoided by not buying the JOE BOBS gas!

George

my famous quote: IF YOUR GONNA BE DUMB YOU GOTTA BE TUFF
 

·
Banned
Cadillac
Joined
·
16,105 Posts
timber6860 said:
I started to use reg 87 in my 93 (4.9) when the gas prices went through the roof a few years back, and I haven't noticed any problems, ie; knocking or pinging. The car still runs smooth, and the mileage is still average 20 mpg. I haven't had the courage to try this with my NS, I just don't drive it as often. (Premium is still over $2.00 in Phoenix!!!!)
That's not too bad, that's per gallon. Where I am it's per litre!! I think 4.5 litres make up a gallon. PS I hate the metric system, if it is so good, then why didn't the U.S. adopt it.:banghead2
 

·
Registered
Joined
·
2,235 Posts
'Cause we started to.....And someone realized it was a stupid, worthless, expensive pain in the ass! So we stayed with what we had.
 
1 - 20 of 43 Posts
Top