Question about 1985 Pontiac Grand Prix

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Gas mileage my car gets 16 mpg. people that have had a car like mine says they got 20-22 mpg. How can i get better.

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  • boog2277 Jun 16, 2008

    Most everything you suggested, I've already had done. I even took the catalytic converter off. That helped about 2 mpg. I'm going to change the transmission fluid to Amsoil. The motor uses too much oil or I'd change it too. The rear end is getting it also. I heard that driving 60mph helps, and it does. I just want more. I think I can get it if I keep trying. Thanks, Boog

  • boog2277 Jun 19, 2008

    The motor smokes every time I start it. I know the valves probably need fixed. Didn't know if that had anything to do with gas mileage. Boog

  • boog2277 Jun 20, 2008

    My car only has 117000 miles and the body is in good shape. No paint work has ever been done to it, a little surface rust on the quarters, so the car is worth spending money on. I have a body shop so I'm in hopes of painting it this winter. Thanks for everything. Boog

  • boog2277 Jun 20, 2008

    I live in Fairview, Ks. 60 miles north of Topeka, Ks.


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Hi Boog!

There are so many variables that affect fuel economy, we could go on for days, but let's check the basics.

I'll assume that you have had the engine properly tuned and that it is running good --- If not start with a good tune-up and oil/filter change.

Anything that increases rolling resistance will hurt fuel economy, such as:

  • Low tire inflation
  • Poor wheel alignment (front AND rear!)
  • Dragging brakes or improperly adjusted parking brakes.
  • Binding/Dragging wheel bearings
  • Bad CV joints
  • Transmission Binds
A chain is only as strong as it's weakest link, and in the case of fuel efficiency, the above links have a cumulative effect --- that is problems in two (or more) areas combine and add up to a bigger drag!

These same things come into play whe trying to improve drag racing performance, so a local racer/performance expert would not be a bad choice to consult with your problem.

Hope this helps, wish I had a magic button solution, but there just isn't one, let us know how it goes and good luck!


Posted on Jun 15, 2008

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  • Bill Bellomy
    Bill Bellomy Jun 19, 2008

    Hey Boog-

    Is the motor burning oil (smoking out the tailpipe), or is it leaking out the oil around gaskets and/or seals onto the ground??? If it is smoking, then your problem is simply worn-out motor... and you are looking at rebuild or replacement... Not much good news, I'm afraid. You COULD verify this by running a compression check or even better, a leakdown test. But new rings and a valve job would probably do wonders!!!



    Sorry I didn't respond to your comment sooner, but I was not e-mail notified of your comment like I should have been, and would not have noticed except for my looking back over my solutions and catching this!


  • Bill Bellomy
    Bill Bellomy Jun 19, 2008


    That is a direct indication of engine wear and efficiency!!! The smoke is from oil mixing into the air/fuel mixture and it adversely affects that mixture. There is an ideal ratio of air to fuel that burns most efficiently (called adiaptic) - this ideal mixture extracts the most energy practically available from a given amount of fuel, and deviations in either direction (rich or lean) result in incomplete combustion --- not all of the energy available in that given amount of fuel is extracted, but instead goes out the tailpipe as unburnt gas (and pollution!) Your car's computer continually tries to adjust the mixture and maps out ideal settings in its memory for different speeds, throttle positions, loads and environmental variables and it constantly readjusts these via feedback from the oxygen sensor, the primary sensor for determining whether an engine is running rich or lean. Since there is not a sensor for each cylinder, it adjusts for the best "average"... If all the cylinders are running close to the same mixture, this works well. But in a worn engine, such as yours, there is usually one or two cylinders that are down on compression or are having oil control issues, and their inability to burn efficiently skews the "average" in a direction away from ideal for the cylinders still trying to work well... and your gas mileage turns to cr*p!!!

    If you think the car is worth it (Still in good shape body and chassis wise) and you can afford it, I would recommend that you buy a rebuilt "short block" (engine block, crankshaft, rods, pistons, and rings) ( and possibly oil pump) preassembled and checked out. You would need to have the heads serviced (grind valves and seats, check springs and replace defectives, new valve guide seals, etc.) and the engine will have to be torn down to and reassembled from short block stage. This would be your most economical way to truly get the engine in shape...

    For more money, you can get a "long block (which is pretty much a complete engine minus accessories and manifolds) which would make the task less complicated... You would not have to go through a lot of complicated head bolt torqueing procedures, for one thing...

    Or as a third option, you can look in the wrecking yards for a good used engine out of a wreck... make sure you see and hear the engine run before spending the $$$!!! It'd be a shame to spend your hard earned money on an engine no better than the one you've got now!

    Hope this explains things in a way that makes sense to you, ...and hang in there!


  • Bill Bellomy
    Bill Bellomy Jun 20, 2008


    You are more than welcome! What part of the world are you in? I have friends all over, and I might be able recommend someone to take real-world look at your ride and perhaps give you a more accurate assessment!


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