'96 DeVille Fuel Economy
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Cadillac DeVille 1985 to 2005 including:
1985-1992 Fleetwood, 1993 Sixty Special, All FWD Forum Discussion, '96 DeVille Fuel Economy in Past Cadillac Vehicle Discussion; Hi I am a new Cady owner and so far i am loving it. One thing though: fuel economy is ...
  1. #1
    Keli is offline Cadillac Owners Member
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    '96 DeVille Fuel Economy

    Hi I am a new Cady owner and so far i am loving it. One thing though: fuel economy is kindda bad. 12 mpg in city. I changed the o2 sensors and still nothing. Could anyone help me? The engine has only 77k on it.

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  3. #2
    rubberbandman's Avatar
    rubberbandman is offline Cadillac Owners Member
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    Re: '96 DeVille Fuel Economy

    I have a 95 Deville and I am also getting horrible gas milage. Is this something that just occured? How is your history with gas milage?

  4. #3
    Eric2203 is offline Cadillac Owners Fanatic
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    Re: '96 DeVille Fuel Economy

    I have a 96 DeVille and I average 21 to 22 mpg. But don't jump to conclusions. I mostly drive on a highway and a reasonably clear road with no stop lights. As soon I use the car for something else, it drops back down a bit.

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    Keli is offline Cadillac Owners Member
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    Re: '96 DeVille Fuel Economy

    That has been the mpg since I bought it. I changed the o2 sensors, had the fuel rail changed, injectors, nothing works. According to Cadillac I should be getting 17 mpg in the city and anywhere between 25-30 on the highway. Instead I am getting 12. Hopefully someone here will know what to do.

  6. #5
    cadillacthrills is offline Cadillac Owners Member
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    Re: '96 DeVille Fuel Economy

    You should be getting around 17city / 22hwy. At 77k your northstar may be due to have its original pugs and wires changed. Be sure to use platinum tip plugs and don't skimp on the wires (if you plan on keeping the car). Replacing the air filter will also help. Do you know if the previous owner used the recommended 90+ octane fuel? Low quality fuel has a dirtying effect on intricate engines like the Northstar. If you are thinking about additives, I have seen improvements with Seafoam in the older 4.9L V8. I have not yet used Seafoam in my Northstar.

  7. #6
    Keli is offline Cadillac Owners Member
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    Re: '96 DeVille Fuel Economy

    Yes the fuel has always been 90+. I`ll ask my mechanic about the plugs and wires. I have always used 90+ gas but a mechanic tld me that car manuals and recommendations are written by company laywers instead of mechanics, so they say used the high octane so they wont be sued. I dont know, but in some level it makes sense.
    Thanks for the tips
    Another thing. Apparently there is a leak in the coolant steel lines that run behind the engine. I can't find that part in the internet. Anybody has any ideas?

  8. #7
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: '96 DeVille Fuel Economy

    Check the FPR. It is located on the right bank fuel rail (firewall side). With the engine running, pull the vacuum hose off and look for fuel leaking out of the nipple. If there is any fuel leaking replace it. If it is leaking you should also be experiencing hard hot starts.

    BTW, the Northstar will run just fine on 87 octane. I have been using it for 2 years now with no effect on fuel milage, I'm averaging 23 MPG (mostly highway). Check the archives, you'll find lots of info on it.

  9. #8
    cadillacthrills is offline Cadillac Owners Member
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    Re: '96 DeVille Fuel Economy

    Quote Originally Posted by Keli
    Another thing. Apparently there is a leak in the coolant steel lines that run behind the engine. I can't find that part in the internet. Anybody has any ideas?
    Don't worry about the coolant leak. The early northstars had them since new. I had to roll my eyes when I read the maintenance tag attached to the radiator shroud cover of a 1996 Concours. It says to add two tablets of stop leak to the lower radiator hose each time the coolant is changed. It says to buy the OEM coolant tablets from cadillac, but you can use Bars Leak from a auto parts store. My Caddy had the same leak and the bars leak fixed it. Try the stop leak. If it doesn't stop the coolant leak try newgmparts.com for replacement parts.

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