: premium at the pump...or is it??

07-17-06, 10:04 AM
I had seen some show like dateline or 20/20 or something like that where the uncovered numerous gas stations that sell thier "premium" unleaded 93 and consumers are actually getting regular or "87" unleaded. The number they uncovered was pretty suprising. My question is, if this is the case does anyone use or recommend an octane booster? Any input would be appreciated.:stirpot:

07-17-06, 10:41 AM
Don't know much about octane boosters. Never use the stuff, but your car will run fine on 87.

07-17-06, 11:24 AM
When I switched from 87 to 93 my mpg went from 22 to 24.5 average city/hwy. So I guess my gas station has "real" premium.

Elmer Fudd
07-17-06, 11:24 AM
Don't know much about octane boosters. Never use the stuff, but your car will run fine on 87.

Yes, the service tech (who I have known for years) at the Caddy dealer told me I is ok to run regular (in fact my manual actually says that - even though it is a 1999) and the worst you may get is a little valve clatter. She owns a 99 herself and says she mixes 93, 89, and 87 octane all the time. If you get some little valve clatter and suspect that stuff you bought at Elmos Discount gas may not have been quite right, I would (and have) just wait until you get 1/4 tank of room and load up on BP/Amaco or Chevron 93. No need to risk adding snake oil boosters, who knows what they do.

Just my thinkin, doesn't mean its right......:bigroll:

07-17-06, 11:59 AM
As far as I know the N* doesn't require premium. However I will agree that I also got better fuel economy by using premium.

As far as octane boosters, I have used many over the years and then stopped when I stopped having hot rods. About a year ago I decided to try some again. After standing in the store for a while I chose the Dale Earnhardt one in the black bottle. At the time it was available from Wal-Mart.

I have to tell you that it's the only time I've added octane booster to a car and could say that I definitely noticed a performance gain. Shortly after that it disappeared form the selves and I haven't seen it since.

07-17-06, 01:06 PM
All Northstars up to and including 1999 require premium fuel. 2000 and up can use regular due to a lower compression ratio. In fact it says "Premium Fuel only" on the instrument panel of my 95.

Elmer Fudd
07-17-06, 01:35 PM
From Owners manual (1999 N* Councours 300hp)

"Use premium fuel rated at 91 octane or higher for best performance. You may use middle grade or regular unleaded gasolines, but your vehicle may not accelerate as well"

So "requires" is a relative term. I would never fill up with 87 since one of the reasons I got this car is that it accelerates like an F-15. However the thread started about what if you get 87 from an unscrupulous dealer --- should you add octane booster....the answer is there is no requirement to do that.

07-17-06, 01:50 PM
Well...... when it says, "USE PREMIUM FUEL ONLY", I take that as a requirement. But from the 1995 "Factory Service Manual", you know, the 2 big books. It says "This Vehicle REQUIRES 91 octane ([R+M]/2 meathod) in orde to ensure proper performance of the fuel control system". This is on page 6C-4 of volume one. So it's not relative for early N*'s. Perhaps since the Deville isn't as performance oriented as the Eldo or Seville they dont say that in the owners manual. Hold on, I'll go get my owners manual and see what it says.

07-17-06, 02:18 PM
OK, I'm back. From the "1995 Eldorado Owners Maual"

In the specifications section in the rear of the manual, page 6-72 it states, "fuel required" (there's that word again) Premium Unleaded (91 Octane OR Higher)

Let me look in the front of the manual.......OK page 6-3, I'll just skip to the good part, "Be sure the posted octane is AT LEAST 91. If the octane is less than 91, you may get a heavy knocking noise when you drive"

Now i've run 87, and no I didn't get a knocking noise, heavy or otherwise. My point is that it is required to run premium, (technically, according to GM) Now apparently GM is contradicting themselves in your case since 99's have the same compression ratio as 95's. I was just kidding about the performance thing. :stirpot:

Elmer Fudd
07-17-06, 02:54 PM
"Now apparently GM is contradicting themselves in your case since 99's have the same compression ratio as 95's. "

Compression ratio is only part of it. I don't know for sure, but I can only assume sometime between 95 and 99 they introduced detonation ("knock") sensors that cause the timing to automatically adjust to the fuel.

just guessing though :confused:

07-17-06, 02:58 PM
All Northstars have knock sensors.:thumbsup:

07-17-06, 03:07 PM
GM just put that "Premium Fuel Only" label on all their Northstars pre-2000 for $hits and giggles. They knew the Northstar would run fine on 87. But when you spend 50k on a car, you want to be able to put the good stuff in it to make you feel like you are putting something special in your special vehicle.

*just my two cents*

07-17-06, 03:16 PM
I agree, as I said, I ran 87. The car ran fine, but I do get more mpg with premium. From 22 to 24.5 is nothing to sneeze at, thats 50 more miles per tank. I get all kinds of shits and giggles with that at todays gas prices. Not only that, as mentioned they do have knock sensors. And if that's not enough for you,..... you can go into PCM overide (PS22) and manually retard the timing 1 to 4 degree's from the base timing of 10 deg BTDC. OK, this looks like another "Premium vs Regular" thread.

07-17-06, 04:56 PM
At some point GM went from Premium "Required" to "Recommended". I forget when. Point is, (per our old Guru) it will run just fine on 87. If you are going to race your buddy and want peak performance, use 92.

07-17-06, 05:05 PM
That's what we were missing,....... the voice of reason. Thanks Ranger

07-17-06, 08:14 PM
OK, this looks like another "Premium vs Regular" thread.

I agree. I think someone should add this type of thread to the Cadillac Technical Archive, so we can send people there for their answer.

07-17-06, 10:30 PM
it seems a simple point - certain cadillac years say use a certain octaine. gm recognised that at 2000 regular fuel was okay - they adjusted the compression ratio to accomodate this, for the consumer.

fact is the NorthStar has beeen set up to notice engine knock and make good on that by adjusting the timing to eliminate it.

think about that for a second....

okay, pretty smart system wouldn't you say.

well, as Ranger has pointed out - 87 octaine fuel will work just fine. as elmer_fudd points out mix it up. try to save $$'s and put fuel in the car. you wanna hi-performance vehicle swich it to nitro and slide in the dirt...

the NorthStar is a really smart engine that GM has totally scoped out. the design/performance has progressed in a consumer focused way [me thinks]. we see single year designs - works in progress. it is what it is - one of the best damned engines around and a high performance one to boot.

what more could you ask for???? gasitupandgo-like hell

07-18-06, 12:00 AM
one of the best damned engines around and a high performance one to boot.

what more could you ask for???? gasitupandgo-like hell

Good conclusion :thumbsup:. It doesnt matter what octane you put in it, whether it be 87,89,91,93.... just gas it up and enjoy a brilliant engine.

07-18-06, 12:48 AM
This is exactly why I go to reputable gas stations. Not a dingy one on the corner selling premium for 5 cents less...

07-18-06, 06:22 AM
thanks for the info....i did have some concerns about valve clatter. but i feel pretty confident that it's nothing to worry about. Anyway i do believe in the news show that this was on, they did point out that this was happening at your mobil stations exxon stations etc, i would hope the number is not high. But i just wanted to ask if it would be a considerable alternative to get 87 and add some octane booster to it. I think with the responses i seen i'll just leave well enough alone and just drive it, i love this car (98 Deville 60,000) and just didnt want to do anything to mess it up.

thanks again....

Elmer Fudd
07-18-06, 09:23 AM
Just a side note...what you really need to NOT do is get gas at a station when the tanker is there (or so I am told - and it makes sense to me). The turbulance in the tank stirs up all the crap that had settled and guess who gets it in their tank??

Also (and I did have my own bad experienec with this) never get gas at a new station for a few weeks. Let someone else get all the dirt, shavings, and dead rats in their cars......:eek:

07-20-06, 11:54 AM
What is this 'valve clatter' some of you are talking about??

BTW on my 95 I can watch it pull timing when I go WOT on 86 octane but at cruising speed and light accel it doesn't pull timing. Thus I get the same power output per unit of fuel, thus the same mileage on any gas.

07-22-06, 02:43 PM
I got a 93 N* and im not sure of the compression ratio, but the need to run 91-93 octane is based one the effeciency of the combustion chamber, piston design, need for total timing, and the material used in the heads. Also there is other factors such as cam duration and lift.

I have a SBC that has iron heads and about 9.2 compression and it HAS to have 93. The piston design is crap and the cam is stock, but the heads are very effeicent (vortecs) and it is running a bit too much timing.

There are too many factors involved to just claim one or another and just because you can hear it detonate doesnt mean that it isnt.

07-24-06, 02:55 AM
There are too many factors involved to just claim one or another and just because you can hear it detonate doesnt mean that it isnt.

See, thing is, it has a sensor to do the hearing for you and adjust timing accordingly. You can even watch it pull timing on OBDI cars.

The compression ratio is 10.3:1, which is high, but it does have aluminum heads.

07-24-06, 09:13 AM
The following thread links to an article written by a GM Design engineer. It explaines detonation very well. It also discusses pre-ignition and the difference between the two:


You are right - NorthStar hears the knock. As it turns out it listens for a certain frequency - and adjusts accordingly. Humans find it very difficult to hear this - plus with all the other engine noises - it can be impossible.

I'm curious as to HOW do you set to OBDI on a 96DeVille to see the ignition changes. What group store/records that. I'm also interested in the fuel flow info at the injectors. Would be neat to watch.

Once watch the fuel guage banks on a passanger flight crossong the Atlantic. KLM student charter out of SU back in the 70's. Actually sat engineer seat for a few hours. No terrorists back then...

07-24-06, 03:05 PM
96 is OBD II.

07-24-06, 04:58 PM
yes - what do I look for?

07-25-06, 01:20 AM
You have to enter the perameters section of the onboard diagnostics (OBDI only). Can't do it on OBDII.

07-25-06, 06:24 AM
well that sucks

07-25-06, 11:59 AM

07-25-06, 02:57 PM
some how I thought OBDII was a bit more sofisticated than OBDI. are you guys sure?? what is the difference between them?

07-26-06, 12:09 AM
Yes it is a bit more sophisticated, but the Guru once said that what it does and how it does it is now mandated by the EPA so we lost all the good stuf it used to do. He always said, don't blame GM, blame the government.

07-26-06, 02:49 PM
Can the timing area be observed? I've got to dig out the shop manual. This has been on my mind for a while.

Problem is my smoker has develoed that summer urge for large pieces of pork and beef brisket!!!

That's not a problem - 14hrs tending a cooker give a guy plenty of time to catch up on his reading...

07-27-06, 12:45 AM
Not sure but I don't think so.

08-01-06, 12:33 AM
With gasoline 'sticker shock' these days, I notice the high cost when I fill up my GMC truck, with 30 gallons of regular. It doesn't seem as bad, when I use 91 in my STS, with a much smaller tank. I always use 91 in it.

By the way....I fill-up at Costco Gas Stations. Today, it was 305 regular, 320 high test. Cheap for California considering 65-85 cents a gal. tax added.

01-01-07, 06:18 PM
In my situation my Eldorado 95 starts acting weird when it has unleaded gas on it ,and i forget to fill up premium (in my town all gas stations have guy that fills up your tank,& unleaded is standard) i pour a octane booster, it fells almost the same but a little weir

01-02-07, 02:14 AM
You must live in Oregon where self-service stations are banned? That's insane.

01-02-07, 02:42 AM
You must live in Oregon where self-service stations are banned? That's insane.
Oregon, the Whackado State.

01-02-07, 05:01 AM
Around here most of the stations have "5 cents of Premium" some have 10 cent off days.

For example Sunoco around the corner has Super Tuesday and Ultra Wednesday. They have 4 levels of gas there, 91/94 for the discount days brings 91 down to 89. The Mobil has Super Monday which brings their 93 down to the price of their 89.

Cheap way to keep the car running at peak they way the factory designed it :)

01-03-07, 11:36 AM
You must live in Oregon where self-service stations are banned? That's insane.

Or New Jersey - we're the same here. AFAIK, we're the only two states to completely BAN self-serve gas pumps.

Although, it's not so bad. Where I am here, we're pretty close to some refineries - Sunoco's Eagle Point Refinery is about 12 miles up I-295. My nearest Sunoco is always 5-7 cents a gallon cheaper than the nearest Sunoco over the Del Memorial Bridge in New Castle, DE. So I can either let the pimple-faced kid pump it for $2.23, or drive an extra 24 miles (round trip) and pay the $3.00 bridge toll, to pump it myself for $2.30 per gallon.

Not a difficult choice.. :)

01-04-07, 12:41 AM
You can go across a city line and pay more for gas due to local taxes costs.

( watch what you vote for!! )

The formula for determining octane changed way back in the '80's.....91 is not real 91 anymore. Just as the "miles per gallon average" for highway driving is at 48.6 mph. So those hi-brids get a 'real-life' average of 60% of the Government test. ....stuff in real life is different than what the government claims.