Terrible mpg 77 Aspen 318

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Slanty

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I just got a 77 Aspen with a 318,2bbl,It runs great but is only getting about 5 mpg,what gives?
 
When you state runs great, how is the acceleration? idle/ cold start? Any trans slippage? Does it have an airconditioning compressor that looks like a V twin? You may be dragging an anchor somewhere. I had a waterpump fan that put a bunch of drag on my 76 and my dads 83 5th did the same. How is your timing set?

Now the easy part: is the gas gauge accurate? Stuck float or sending unit. You should be getting 15 mpg if you are driving conservatively. That means no faster than 55 mph and stayoff the hard accelerations. These non overdrive cars are not like modern 4, 5 or 6 speeds. If you trans is winding out between gears, you are throwing gas right out the exhaust and not to the tires
 
Another thing to consider is your universal joints.
The one's on my Fifth were almost seized...
I got them replaced and my gas mileage almost doubled.
And like Billy said....how well is it running in all the aspects he mentioned?
When is the last time it had a full tune up?
 
Are the brakes dragging? Lift the vehicle & spin each wheel by hand. That will aid in finding any binding elsewhere on the vehicle
 
dont forget something as simple as the front wheel bearings could be bad or to tight causing a ton of drag just like the brakes can
 
there is a long list of things that can cause poor milage as listed before.. a dirty air filter, draging a/c or alt can bog engine down. timing can be off. i got a free 5th ave from my father in law and it got maybe 5 mpg. give it a good oil change and change plugs, i use champions gapped at .045 and check your timing, you cant always go by the timing marks on old engines, i adjusted timing by advanceing a bit at a time till it ran the best with out pinging-knocking. i found that my engine likes the timing advanced far enough that the housing is turned fully advanced ,it cant turn any farther. does your 318 have leanburn? if so ,maybe there is problems with the puter and or carb-dist. best thing to do is check everything that you can do to your car to optimize the running, brakes-driveline- transmission, change fluid and filter not forgetting to adjust bands to factory service manual specs. my car now gets 12 to 14 on the hiway, could be better but ill give her more care as soon as winter gets done freezing us out,lol
 
Well if you say it's running great I would guess no pinging, brakes not dragging cause you would smell them and feel the drag (most likely). Have you checked for fuel leaking when running? I would think you'd smell that too, but depends on whether you park outside or in a garage. That's just so low it makes me think you are losing it to a leak or syphoners.
 
LSM360 said:
Well if you say it's running great I would guess no pinging, brakes not dragging cause you would smell them and feel the drag (most likely). Have you checked for fuel leaking when running? I would think you'd smell that too, but depends on whether you park outside or in a garage. That's just so low it makes me think you are losing it to a leak or syphoners.
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It's definitely something cause that's brutal mileage....
 
alf44 said:
dont forget something as simple as the front wheel bearings could be bad or to tight causing a ton of drag just like the brakes can
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That'd what I meant by binding elsewhere. I guess I should've said it. Thanks, Larry
 
My imp said:
That'd what I meant by binding elsewhere. I guess I should've said it. Thanks, Larry
Click to expand...

That's also why I mentioned U joints.
Could hardly notice how bad mine were till they started squeaking.
Like I said....after I changed them my mileage almost doubled.
 
Hey Slanty, make sure you let us know what you find. Don't leave us hanging. You may find something we've never seen before, & that's how we exchange info here. Thanks, Larry
 
Yea man, our sick minds want to know. Even if you just have a 500 pound right foot as the problem all along, that's cool, we all on here have that same issue with our right foot.... IT's OK, everything will be OK. Bad right foot, bad right foot! Ain't it terrible when a right foot has a heavy addiction. We can get you through this.
 
Somethings either leaking or rubbing.....or yeah..you have no police there and you just have a lead foot. :glasses2:
 
even treating the gas pedal like there is a egg under it, we still end up with scrambled eggs,lmao
 
The fan clutch seemed to be sticking so I took The fan off,and adjusted the timing,now I'm getting 12.
 
i need to swap the clutch fan on mine for a fixed fan to see if that helps me
 
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