is it necessary to run only premium fuel, or can regular unleaded be used?

premium fuel will give you the maximum horsepower and economy- if you don't use premium it will still run, but you won't get the most out of it, and if it knocks, go back to the premium- DON'T USE E85 (ETHANOL).

Some engines require premium to work properly. Check the manual or there could be a label inside the fuel trap. Modern engines have (knock) sensors that adjust to any type of fuel, so even though premium may be recomended, it will still run without problem on regular. As for performance and fuel economy, the extra cost of premium usually does not compensate for any savings in fuel economy (but! it has less emissions). Pperformance wise the difference is barely noticeable most of the time. You can also call a Cadillac dealer and ask.. its free.

high output engines like the north star V-8 are happyest with premium fuel .....period !

My husband once put regular in my 99 eldorado. You can really tell the difference. It doesn't run smoothly. The engine in that car is so smooth and powerful, it deserves the best. I use the highest octane I can get and she purrs.

I should have given you a better answer the first time. I have an 99 Eldorado and my husband has an 04 Seville. Both have almost the same 32 valve Northstar V-8. The eldorado takes premium and the seville takes regular. The ride in the seville is nice but it can't touch the performance of the eldorado. He tried the regular in the eldorado once because he thought same engine, same gas would be fine. The engine did not knock, but it didn't feel the same. I just use premium, a high performance engine is just that. You're talking about 20 - 40 cents a gallon. Enjoy the engine, you won't be sorry.

CHEERS RUBY !

Gasoline has the same burn rate whether it is 87 octane or 93 octane. The compression ratio of the engine will determine what type of fuel you should use which should be in the driver handbook for you automobile. Higher compression engines require a more stable fuel (Higher Octane) to prevent the fuel igniting uncontrolled. If your engine has a lower compression ratio and only requires 87 octane fuel, then you're wasting money on the premium fuel. You will not get more power out of your engine this way. However, If your engine requires 93 octane to prevent Knock (Which is ignition of the fuel before the spark does it) then this cost you power. The knock sensors retard the timing to allow for this fuel but at a loss of power meaning your mpg's will suffer because you have to push harder on the gas pedal to maintain the same speeds you would at the higher HP.

I should have made one more thing clear on the premium fuel. I said that engines with lower compression ratios requiring only 87 octane fuel wouldn't benefit from using premium. That isn't entirely true. Some premiums have additives that help clean your carbon buildup, etc. Those additives do help with those types of things but only for cleaning purposes, not more powerful fuel.

What?! You still have 87 and 93 octane fuel in the USA? It's strange... I live in europe, and here we only have 95 and higher! 95 is the lowest octane gasoline you can get here. It's pretty much the standard everywhere in europe. Wow!

I switched to regular for a few months - no knocking - BUT I SWITCHED BACK to 93 octane because the car wasn't performing as well as I had come to expect. 1994 deville 4.9 runs better and better mileage with 93 and I'd switch to 95 if I could get it

Many cars that say Premium only (such as most German cars) will run just fine on Mid-Grade which is 89 Octane. In many cases however, 87 octane will not run well in those cars. Regardless of Grade - try to stick with Tier 1 gasoline because it has more additives than the minimum required by EPA.

I just purchased a 1997 eldorado 57,400mi. Do I have to run premium

Cadoo, to get the full horsepower, yes, if that doesn't matter to you, then no.

Thanks Richard just saw post

Any thoughts on a 96’ Cadillac Deville? Im wondering if using regular gas would affect it, on the dash it reads “premium unleaded fuel only.”

I accidently put nearly 18 gallons (from E to F) of regular unleaded (87 octane??) in 95 eldorado instead of premium unleaded.To not take any chances of engine knocking/ping, I bought siphon pump at walmart but assuming caddy has anti-siphon baffle since it wouldnt suck any gas out. It's my mom's car.I'm female.Please help with suggestions.I only drove it 5 miles back home and it hasnt been driven since because dont want to take any chances. Dealership rep said it will be fine but friend did this to boyfriends car and ruined the engine.

got a 1996 devile it says premium only ,i been using 87 octane vales are clicking will the 93 octane stop the vales from pecking this has just started