: New Northstar, Unleaded or Premium?



Slick Black Cadillac
06-28-04, 12:23 AM
Cadillac supposedly "re-designed" the Northstar in 2000 to run off of unleaded gas. After that conversion does it hurt the motor to continue to run premium in the Northstar (2000 DHS). I was under the impression that running premium would be better for the motor because it burns hotter and cleaner resulting less carbon build up. However, a few cars I have owned couldn't run premium because it damaged them. Just dont want to wreck my new Caddy.

BeelzeBob
06-28-04, 12:20 PM
Well.....I assume you mean regular vs. premium as all gasolines are unleaded these days...???


The 2000 and later Northstars are designed for optimum operation on regular (unleaded) fuel. They will run fine on it. The compression ratio of the 2000 and later engines was modified along with the combustion characteristics of the combustion chamber (new heads) as well as the EGR rates and spark timing in the PCM. Regular in the 2000 and later engines is perfectly fine and there is little or nothing to gain by running premium unless you are in a harsh environment (such as Death Valley in the summer....Phoenix city traffic when it is 110...etc...) where there might be some slight level of spark retard from the knock control system to prevent detonation on regular.

Regular fuel and premium fuel "burn" at the same rate and temperature....so there is nothing to the tale of running premium improving combustion or burning hotter or cleaner.....

What engine could be "damaged" by running premium fuel???

Premium fuel just resists spark knock or detonation better than regular fuel since it has a higher octane rating. Nothing in premium would damage an engine...but if the engine is tuned or designed to run on lower octane rated fuel then the use of premium is simply not necessary.

eldorado1
06-28-04, 02:08 PM
So what are 93-99 engines supposed to be run on? I don't have an owners manual or anything to reference... 91 octane?

lowscola
06-28-04, 02:12 PM
So what are 93-99 engines supposed to be run on? I don't have an owners manual or anything to reference... 91 octane?

You can find 93+ year owners manuals at: http://www.mygmlink.com/pdf/go2content/manual/US/en/cadillac/

eldorado1
06-28-04, 02:18 PM
You can find 93+ year owners manuals at: http://www.mygmlink.com/pdf/go2content/manual/US/en/cadillac/
For a second I thought that was a link to buy an owners manual... That's a handy resource there! Looks like it's 91 octane for me. Thanks,

BeelzeBob
06-28-04, 02:23 PM
So what are 93-99 engines supposed to be run on? I don't have an owners manual or anything to reference... 91 octane?

That generation of engine is optimized for premium fuel. Premium was "required" for the first few years of Northstar production. Around 1997 the fuel requirements were changed to premium "recommended" and premium was removed from the dash and filler cap.

Regular fuel will run fine in most all of the 93-99 engines under most conditions. The engines have a very effective knock control system that will protect the engine is lower octane fuels are used with little or no apparent driveability impact. So, using regular is fine in a 93-99 engine. If you notice degraded drivability (sags, hesitations, loss of power) on the regular octane fuel in hot, dry ambient conditions then you might want to try a better octane grade of fuel...but the engine will not be damaged nor care.

The 93-99 engines had a very tolerant combustion chamber that was fairly knock resistant and lost very little power or driveability when the knock control system retards the spark because of detonation. For this reason and sufficient field experience running on regular fuel the "premium only" requirement was dropped.

The 93-99 engines have more compression and are definitely tuned for premium and will not make full power nor get full fuel economy if a lesser octane fuel is used. But most all drivers will not notice the difference.

Use regular and try it. Unless you live and drive in Phoenix city traffic all the time in the summer or are planning on towing a trailer thru Death Valley in the summer regular fuel will be fine. If you are planning a track day with your STS or are racing your buddy for pinks then use premium for maximum power. Otherwise, a 93-99 will be fine on regular most all the time.


A 2000 and later Northstar engine will be fine on regular period as it was designed and tuned for regular from the beginning.

JohnnyO
07-04-04, 07:32 AM
:coolgleam Thanks bbob. My mom's '99 Eldorado calls for premium unleaded on the fuel gauge, my dad's '04 DeVille does not. I had wondered what the differences were.

BeelzeBob
07-04-04, 07:02 PM
Even the 99 Eldo will run fine on regular under most all conditions and it will certainly not harm the engine to run it on regular. The requirement for the premium fuel was dropped before 99 and the words "premium" fuel were eleminated from the fuel cap and dash cluster...on all but the Eldo. Since that car had a limited life span and was not planned on being retooled the dash was left alone so the words "premium" stayed there for a few years... It really isn't absolutely necessary unless it is an extreme climate (hot and dry) and/or you want to be absolutely sure of maximum power.




:coolgleam Thanks bbob. My mom's '99 Eldorado calls for premium unleaded on the fuel gauge, my dad's '04 DeVille does not. I had wondered what the differences were.

JimHare
07-06-04, 12:09 PM
BBO posted:

The requirement for the premium fuel was dropped before 99 and the words "premium" fuel were eleminated from the fuel cap and dash cluster...on all but the Eldo.


My 99 Deville still has "Premium Fuel Only" on the dash panel - not sure about the cap/filler door.

I've run Mobil Reg, Special and Premium, and Sunoco Super and Ultra, and not noticed a major difference. Have never heard a knock from the engine either, to the best of my knowledge. Drive the car medium-hard (old enough to know when it doesn't pay to drive like a fool, and young enough to want to drive fast so you young whippersnappers don't consider me an "old man" style driver.. lol..

BeelzeBob
07-06-04, 11:11 PM
Must be my memory. Maybe I'm thinking about the 2000 year model when the premium fuel was deleted from the dash on the cars except for the Eldo....duh...




BBO posted:

The requirement for the premium fuel was dropped before 99 and the words "premium" fuel were eleminated from the fuel cap and dash cluster...on all but the Eldo.


My 99 Deville still has "Premium Fuel Only" on the dash panel - not sure about the cap/filler door.

I've run Mobil Reg, Special and Premium, and Sunoco Super and Ultra, and not noticed a major difference. Have never heard a knock from the engine either, to the best of my knowledge. Drive the car medium-hard (old enough to know when it doesn't pay to drive like a fool, and young enough to want to drive fast so you young whippersnappers don't consider me an "old man" style driver.. lol..

JimHare
07-08-04, 11:26 AM
:worship:
BBob-
Considering the overwhelming amount of technical expertise and information you have disseminated, I would not consider it a major faux pas...

:)