Can I Use 87 Or Do I Have To Use Premium Fuel In My 99 Seville STS ? -NEW DRIVER PLEASE HELP !


Asked by CadillacLivin Apr 14, 2013 at 03:11 PM about the 1999 Cadillac Seville STS

Question type: General

5 Answers


You can use 87. The knock sensor will retard the ignition if it's not good enough and you will have less power and worse MPG's. Run two or three tank fulls, write down the gallons and mileage to determine your MPG's. Run two or three tanks of the next grade up and do the same. If you are getting better MPG's, use the higher grade gas. It costs less per mile and it's better for your engine. Keep track of your numbers at

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Okay , Thank You Soo Much ! :) Appreciate It .


the car will tell you right on the dash board to use premium if it does then that's what you use

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Best Answer

tenspeed is correct. Most any GM car will run on 87 Octane. It should be less power and mileage - but depending how you drive, you may not notice it. IF you get pinging or knocking on acceleration - then move up to the next Octane level. Sticking with a good brand of gas is important. Try to avoid the 'no-name' stations whenever possible. Their prices are usually lower because their gas is 'older' or has less cleaning additives.


I bought a 99 sts with 200 k then found this 4.6 has over 10:1 compression. DO NOT run anything less than premium! Dont rely on knock sensors. The reason these engines crap out head gaskets is people try running regular 87. When u hear a ping or knock, what is actually happening is an uncontrolled combustion process. This results in way higher cylinder pressures which strip the head bolts (which are too small to tolerate it) out of the block! Hence your head gasket didnt fail, your bolts did! Ive put 50 k on my caddy in 6 months. It see's routine w.o.t.up the b.c. mountains and its performed way past the so called "head gasket" expiry date with out issue!

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