Eldo Man
LVC Member
Does the northstar in a 93 and up eldorado require premium fuel?? or can you use regular and mid-grade?? please help me with this im trying to buy the car soon. :feedback
Northstar Decision?
- Thread starter Eldo Man
- Start date
Northstar and Premium Fuel
No, the Northstar engine is not required to use premium fuel. I use regular gas in my 94 N* without any problems. The N* has an anti-knock feature which adjusts the timing to prevent knocking. The 93-95 Northstars had the knock sensor on the outside of the block on the right hand side of the engine beside the trans. From 96 on the sensor is under the intake. Premium gas can be used if you notice knocking. Otherwise, regardless of the recommendation, you can use regular gas (87 Octane).
Below is information from a Cadillac engineer known as bbobysnki regarding regular v. premium fuel:
If the engine in question was designed and optimized for premium then using lower octane fuels will cause a loss in performance and fuel economy. If the engine in question has a knock sensor it can probably protect the engine in the event of spark knock but it does that by reducing the spark advance...causing a loss in performance and fuel economy.
The "computer" can only take evasive action to prevent or minimze spark knock.... It cannot improve the octane rating of the fuel. If the engine was optimized for maximum power on premium then the computer cannot correct for regular fuel, eliminate detonation and still deliver the same level of performance.
On certain engines, your mechanics recommendations are partially true.... Unfortunately, you do not have one of those engines. He should have picked up on this. A 4.9 does NOT have knock sensor and cannot detect knock or protect the engine against detonation. Having said that, if you try midgrade or regular and do not notice any detonation then it is fine. If you do notice detonation, then you can have your mechanic retard the spark advance several degrees on the 4.9 and that should enable the engine to run fine on regular with no spark knock...but it will not have quite as much performance (HP) and the fuel economy will suffer.
A Northstar engine has a very sophisticated knock control system and can tolerate regular fuel quite well. Due to the excellent combustion characteristics of the Northstar cylinder head and combustion chamber there is very little power loss and very little loss of driveability and fuel economy with the spark retard the system uses to prevent detonation. This is all in the characteristics designed into the engine and the combustion chamber and is different on all engines.
In Answer To A Question Regarding Premium Required & Recommended:
The 96/97 Northstars actually went from a "premium required" to a " premium recommmended" fuel requirement. The premium fuel "required" was eliminated from the dash and gas cap on the 97 models I think.... That was done purely because the 93/99 Northstar engines are very tolerant of mid grade and regular fuel under most all conditions. The engine compression ratio and combustion chamber was not modified in the least to do this. The engine is still optimized to make the most power on premium fuel. They will not necessarily make full power on lower octane fuels but they drive fine and will not be damaged at all.
The 2000 and later engines are completely redesigned and the combustion chamber and compression ratio were modified substantially to allow operation on regular fuel. Under some severe conditions (very hot , dry weater) the use of premium might add a little power but for most all of the people in most all of the driving conditions in the US the use of regular in the 2000 and later engines is fine.
Despite your observations there is no way that the use of regular fuel caused any damage to the spark plugs or wires. Both the earlier engines and the 2000 and later engines are tested on regular fuel for spark plug preignition resistence to make sure that nothing will be damaged by lower octane fuels. The quality of the fuel you bought may have had an effect on spark plug deposits or something...but that had nothing to do with the octane rating of the fuel.
Difference Between Pre-Ignition And Spark Detonation:
There is a big difference between a phenomenon called pre-ignition and another, related but different phenomenon called spark knock or detonation.
If the end gas in the chamber spontaneously combusts due to heat and compression from the normally burning mixture that is called detonation or spark knock. Key here is that it occurs AFTER the spark plug ignites the mixture normally. The mixture ignites, burns and if the end gas gets too hot or too compressed it spontaneously combusts. The octane rating of the fuel tells how well it resists this spontaneous combustion. Detonation or spark knock makes the characteristic "pinging" or "knocking" marbley noise from the engine.
If the fuel/air mixture ignites BEFORE the spark plug arcs as suggested then that is called preignition. The mixture will NOT just spontaneously combust under those conditions...it needs an ignition source such as an overheated spark plug electrode or glowing carbon deposits in the chamber to ignite it before the spark. There is simply not enough compression in a gasoline passenger car engine to spontaneously ignite or combust the mixture. Since the phenomenon of pre-ignition requires an alternate ignition source increasing the octane rating of the fuel will not prevent pre-igntion. Octane rating has virtually no affect on pure preignition. Also, you cannot hear pre-ignition and 9if preignition occurs it is almost a guaranteed engine destroying event. Holes in pistons most likely.
Diesel engines have enough compression to ignite the fuel (that is why they are called compression ignition engines), not "spark ignited" gasoline engines.
A Northstar engine will absolutely not be damaged by running it on regular fuel. If you are going to race thru Death Valley or tow trailers thru there in August I would recommend premium fuel for maximum performance but there won't be any engine damage if you use regular. A Northstar of any year will run forever on regular fuel with no damage.
Regarding MTBE & Fuel In General:
I honestly don't think you are going to see significant deposits caused by the fuel in either case. Some premium fuel, particularily fuel with MTBE, will leave yellowish or yellow-greenish deposits on the spark plugs...but it is more just coloration than real heavy deposits.
Fuels have changed significantly over the years as the change was made from carburetors to fuel injection and port fuel injection. There are detergents in fuel that prevent intake valve deposits, exhaust valve deposits, combustion chamber deposits, injector deposits, carb bowl deposits, etc...... These detergents have changed over the years in chemical makeup, concentration, etc. At one point in the mid 80's most of the oil companies eliminated the carb deposit detergents as they "weren't needed" since most all the new engines had fuel injection. Guess what that led to....the spate of injector tip deposits. At another point in the late 80's the detergents changed and intake valve deposits became a real issue as the intake deposit formation caused drivablitliy problems on many port fuel injected engines due to the deposits acting like a "sponge" on the intake and causing hesitations when accelerating.
A lot has been learned on this and the learning continues. I think that the injector designs and tolerance for intake deposits has been accounted for in engine design to some degree but the oil companies have also learned what detergents are important and include them to a majority degree. Obviously, in a given area, all the "gasoline" stock comes pretty much from the same terminal so the only difference is the additive package (including the detergents and solvents) added to the fuel. Cheap fuel at cheapie stations may be cheap for a reason....little or no additives or detergents.
There isn't anything inherent in the octane rating of the fuel itself that causes more or less deposits and it all burns at the same rate and temperature so deposit (soot) formation should be about the same regardless of octane rating.
Asuming, of course, that the fuel is all unleaded. LEADED premium, where more and more tetra-ethyl lead was added to the fuel to increase the octane rating, would certainly cause more deposits due to the lead. And the more lead, the more deposits. So maybe the old wives tale of premium and deposits stems back from the leaded fuel days.......hm......maybe another myth explained.
Eldo Man said:
No, the Northstar engine is not required to use premium fuel. I use regular gas in my 94 N* without any problems. The N* has an anti-knock feature which adjusts the timing to prevent knocking. The 93-95 Northstars had the knock sensor on the outside of the block on the right hand side of the engine beside the trans. From 96 on the sensor is under the intake. Premium gas can be used if you notice knocking. Otherwise, regardless of the recommendation, you can use regular gas (87 Octane).
Below is information from a Cadillac engineer known as bbobysnki regarding regular v. premium fuel:
If the engine in question was designed and optimized for premium then using lower octane fuels will cause a loss in performance and fuel economy. If the engine in question has a knock sensor it can probably protect the engine in the event of spark knock but it does that by reducing the spark advance...causing a loss in performance and fuel economy.
The "computer" can only take evasive action to prevent or minimze spark knock.... It cannot improve the octane rating of the fuel. If the engine was optimized for maximum power on premium then the computer cannot correct for regular fuel, eliminate detonation and still deliver the same level of performance.
On certain engines, your mechanics recommendations are partially true.... Unfortunately, you do not have one of those engines. He should have picked up on this. A 4.9 does NOT have knock sensor and cannot detect knock or protect the engine against detonation. Having said that, if you try midgrade or regular and do not notice any detonation then it is fine. If you do notice detonation, then you can have your mechanic retard the spark advance several degrees on the 4.9 and that should enable the engine to run fine on regular with no spark knock...but it will not have quite as much performance (HP) and the fuel economy will suffer.
A Northstar engine has a very sophisticated knock control system and can tolerate regular fuel quite well. Due to the excellent combustion characteristics of the Northstar cylinder head and combustion chamber there is very little power loss and very little loss of driveability and fuel economy with the spark retard the system uses to prevent detonation. This is all in the characteristics designed into the engine and the combustion chamber and is different on all engines.
In Answer To A Question Regarding Premium Required & Recommended:
The 96/97 Northstars actually went from a "premium required" to a " premium recommmended" fuel requirement. The premium fuel "required" was eliminated from the dash and gas cap on the 97 models I think.... That was done purely because the 93/99 Northstar engines are very tolerant of mid grade and regular fuel under most all conditions. The engine compression ratio and combustion chamber was not modified in the least to do this. The engine is still optimized to make the most power on premium fuel. They will not necessarily make full power on lower octane fuels but they drive fine and will not be damaged at all.
The 2000 and later engines are completely redesigned and the combustion chamber and compression ratio were modified substantially to allow operation on regular fuel. Under some severe conditions (very hot , dry weater) the use of premium might add a little power but for most all of the people in most all of the driving conditions in the US the use of regular in the 2000 and later engines is fine.
Despite your observations there is no way that the use of regular fuel caused any damage to the spark plugs or wires. Both the earlier engines and the 2000 and later engines are tested on regular fuel for spark plug preignition resistence to make sure that nothing will be damaged by lower octane fuels. The quality of the fuel you bought may have had an effect on spark plug deposits or something...but that had nothing to do with the octane rating of the fuel.
Difference Between Pre-Ignition And Spark Detonation:
There is a big difference between a phenomenon called pre-ignition and another, related but different phenomenon called spark knock or detonation.
If the end gas in the chamber spontaneously combusts due to heat and compression from the normally burning mixture that is called detonation or spark knock. Key here is that it occurs AFTER the spark plug ignites the mixture normally. The mixture ignites, burns and if the end gas gets too hot or too compressed it spontaneously combusts. The octane rating of the fuel tells how well it resists this spontaneous combustion. Detonation or spark knock makes the characteristic "pinging" or "knocking" marbley noise from the engine.
If the fuel/air mixture ignites BEFORE the spark plug arcs as suggested then that is called preignition. The mixture will NOT just spontaneously combust under those conditions...it needs an ignition source such as an overheated spark plug electrode or glowing carbon deposits in the chamber to ignite it before the spark. There is simply not enough compression in a gasoline passenger car engine to spontaneously ignite or combust the mixture. Since the phenomenon of pre-ignition requires an alternate ignition source increasing the octane rating of the fuel will not prevent pre-igntion. Octane rating has virtually no affect on pure preignition. Also, you cannot hear pre-ignition and 9if preignition occurs it is almost a guaranteed engine destroying event. Holes in pistons most likely.
Diesel engines have enough compression to ignite the fuel (that is why they are called compression ignition engines), not "spark ignited" gasoline engines.
A Northstar engine will absolutely not be damaged by running it on regular fuel. If you are going to race thru Death Valley or tow trailers thru there in August I would recommend premium fuel for maximum performance but there won't be any engine damage if you use regular. A Northstar of any year will run forever on regular fuel with no damage.
Regarding MTBE & Fuel In General:
I honestly don't think you are going to see significant deposits caused by the fuel in either case. Some premium fuel, particularily fuel with MTBE, will leave yellowish or yellow-greenish deposits on the spark plugs...but it is more just coloration than real heavy deposits.
Fuels have changed significantly over the years as the change was made from carburetors to fuel injection and port fuel injection. There are detergents in fuel that prevent intake valve deposits, exhaust valve deposits, combustion chamber deposits, injector deposits, carb bowl deposits, etc...... These detergents have changed over the years in chemical makeup, concentration, etc. At one point in the mid 80's most of the oil companies eliminated the carb deposit detergents as they "weren't needed" since most all the new engines had fuel injection. Guess what that led to....the spate of injector tip deposits. At another point in the late 80's the detergents changed and intake valve deposits became a real issue as the intake deposit formation caused drivablitliy problems on many port fuel injected engines due to the deposits acting like a "sponge" on the intake and causing hesitations when accelerating.
A lot has been learned on this and the learning continues. I think that the injector designs and tolerance for intake deposits has been accounted for in engine design to some degree but the oil companies have also learned what detergents are important and include them to a majority degree. Obviously, in a given area, all the "gasoline" stock comes pretty much from the same terminal so the only difference is the additive package (including the detergents and solvents) added to the fuel. Cheap fuel at cheapie stations may be cheap for a reason....little or no additives or detergents.
There isn't anything inherent in the octane rating of the fuel itself that causes more or less deposits and it all burns at the same rate and temperature so deposit (soot) formation should be about the same regardless of octane rating.
Asuming, of course, that the fuel is all unleaded. LEADED premium, where more and more tetra-ethyl lead was added to the fuel to increase the octane rating, would certainly cause more deposits due to the lead. And the more lead, the more deposits. So maybe the old wives tale of premium and deposits stems back from the leaded fuel days.......hm......maybe another myth explained.
esperman
New LVC Member
the 97 have premium required. it wasnt until a mild redesin in 2000 where the 4.6 went recommended. stay with premium..especially if its not Shell or BP...the heads WILL carbon up. If you can afford a northstar..you can afford premium.
Nakoa
Well-Known LVC Member
esperman said:
then explain all the broke ass g dogs with a caddy they picked up for 2000. hahaha
hottweelz
Dedicated LVC Member
Less then 93 Octane and mine pings. Period.
As Mac1 has stated your Caddy can run on regular gas and not have a problem. My 96ESC has received regular gas after I read numerous post on the Caddy forum. This subject had been beat to death. Don't let the company recommends premium gas guys affect your decision. It has been stated many many times the N* has a anti-knock feature that will correct this, but if you have the extra 20cent per gallon to spare go right ahead.
natural gas
LVC Member
For 4 or 5 bucks more a fill up, I burn only Shell 93 V power for my sweet 94 Eldo. Case closed for me.:C
MediumD
Dedicated LVC Member
If you feel the need to throw away $.20 per gallon you burn, or if your car has a malfunction, go ahead and run premium. As for me, I run premium when I go to the track and for the occasional night of street racing.
taylor414ce2003
Dedicated LVC Member
my 1999 recomends premium fuel only-
MediumD
Dedicated LVC Member
We know. All the 99 and older say that. But in reality, they do not (or at least should not if they are in proper working order, period.)