95 Deville Fuel - Regular or Premium

[RodJ44137]

My ex bought 95 Deville about a month ago w/ 134K miles. Her husbanc says local mechanic said it's alright to use regular (87 octane) fuel, but I read in the manual it has to be at least 91 octane (premium).

Does this engine REQUIRE premium fuel?

Thanks!

[Cadillac Jim]

The bottom line is that it is OK to run a 1995 Deville on 87 octane gas. I believe that you have the 200 hp 4.9 liter overhead valve engine, not the 300 hp Northstar (which the Concours has). The eights digit of your VIN will be a B if you have the 4.9 or a 9 if you have the 300 hp Northstar.

There has been a lot of discussion on the grade of gas here. A lot of people run the 1993-1999 Northstar on 87 octane, and I have had gas station attendants here tell me that most people run 87 octane in their older Cadillacs. I am careful to stipulate "93" when I buy gas because otherwise the attendant will put 87 in it.

Many say that it is OK to run 1993-1999 Northstars on 87 octane gas. I've never even tried it, in 10 years of owning my car and 130,000+ miles, so I would say to ask others about their experiences.

My take about running 87 versus top tier gasoline in a Northstar:

ADVANTAGES

• Cost.

DISADVANTAGES

• Lower performance.

• Less detergent additives -- more likely to need injectors cleaned, more susceptible to moisture in the fuel system.
• Lower gas mileage; you get slightly less miles per tank.

My take about running 93 octane gas in my 300 hp Northstar:

ADVANTAGES

• Performance. For me, you can stop there.

• Highest level of detergent and other additives. do a search here on "top tier gasoline" with the quotes and see what I mean.
• More miles per tank, particularly on the highway.

DISADVANTAGES

• NONE

Cost is equivalent, in my opinion. Many years ago I found that running high octane gas in my car, with the spark advance adjusted to take full advantage of the increased octane, I got better fuel economy that offset the added cost. I also found that this really old car ran cooler and, of course, it had added performance. Newer cars automatically adjust spark advance to account for fuel octane, and the Northstar certainly does that, although I'm not sure about cars designed for 87 octane taking advantage of 93 octane through their PCM adjustments and the knock sensor. At one point, someone on this forum did a calculation and showed that the slight increase in gas mileage offset the difference in cost, although others will disagree.

[Ranger]

'95 Deville has a 4.9. The 4.9 does not have a knock sensor so it is unlikely you'll get away with 87 octane without knocking. Maybe 89. Try it an see. If it knocks, go back to premium.