how to increase mpg

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Bock120

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Have a 63 valiant with 170 slant 6 and getting about 10 mpg. Anything I can do to increase the mpg? looking for easy and inexpensive fixes.
 
You need to diagnose what's wrong. It should be getting right about twice that. Do you have a factory service manual for the car? That's the first thing I would get. FACTORY, not Haynes or Chiltons or anything else. You can find them on Ebay. I would check things like tune up, and the general well being of the engine through a compression test. Check the air cleaner to make sure it is good and clean. Check the exhaust system to make sure it's not restricted by a collapsed pipe or stopped up muffler. Look at the plugs. Are they fresh? What color are they? If they are a dry sooty black, that indicates a rich mixture such as carburetor problems. Does it still have a point type ignition? They can be a source of contention if they are left unattended for long periods. They run very well if they are maintained, but over time if they are neglected, they can become out of adjustment since the points actually burn up slowly over a long period and the points rubbing block wears. All of this will cause changes in ignition timing and certainly cause bad mileage.
 
Yeah, you ougtha be getting close to 23-25 easily driving on the highway at 60 mph.

Are you lead footing it? (just asking) It this an auto or manual trans? Do the brakes work well or is there any thing weird feeling in their action?

How does the car run in general while cruising? Smooth or rough? How does it idle? Smooth or rough?

Most likely issue (but not the only possible issue) is that the carb is flooding partially and dumping a lot of excess fuel in the intake. After warming up, take off the air cleaner, shut the engine off, and look down the carb throat and see if gas is dripping into the throat (and listen for it dripping too).

Check the plugs as above for fluffy carbon, which is a sign that there is excess fuel (running rich).

Have you rebuilt a carburetor, or do you have the skills and tools to think you can tackle that?
 
serious problems at 10mpgs.

step 1, complete tune up. air and fuel filter, Plugs, wires, points, rotor cap, timing, valve adjustment, carb tune, compression test, check for any vacuum leaks, etc. your car will love this anyway. Do the oil while youre at it.

reevaluate

step 2 rebuild your carb. its cheap and easy.

reevaluate

step 3 check out the tranny. it MAY be slipping.

10MPG is acceptable if you had a 440.
 
are you always driving up hill in a head wind?

members have given you great suggestions, you need to figure out the health of your car right now-- what timing is running, are the valves adjusted, is the carb functional, exhaust leak? Heck are your tires low on air pressure-- that can cause major MPG loss.

do these things before spending $$ on parts--- get a base line for your ride-- then replace the worn parts with good new ones(there are some really crappy parts out there).

Lawrence
 
I used to get 20 MPG with a worn out 170 slant....
 
here is my idea. if MPG is down the first thing to check is the distributor vacuum advance. second check the cap, wires, plugs. if the cap has a vent hole next to the center tower. plug the hole with JB-weld.
 
After driving check the rims for excessive heat. Would indicate dragging brakes
Jack the car up and check to see if the wheels spin easily.
Look for uneven tread wear.
 
I think I'm getting better than that with my 360 that I'm still tuning! Something isn't quite right.
 
Sounds like you might want to do a "coast down" test to see if you have some excessive drag somewhere. Maybe get a friend to go out on a flat country road and hit 50-60 side by side then hit neutral together and see what happens. If he is behind you when you accellerate and loses sight for the smoke, maybe the choke is stuck closed. A /6 should do much better than 10 MPG.

Do you have enough air pressure in the tires? Oboma said if you properly inflate them you can get 50 MPG. LOL.
 
10 mpg is reasonable if you live in the mountains. I got 22 mpg average hwy in my 69 Dart slant for decades, in flat land. The best way to get mileage is to never use the brakes. Everytime you brake, you waste energy. Ride a bicycle and you will appreciate. The 70's "gas crisis" recommendations to "accelerate like an egg is under the pedal" is only partly true. A gas engine is actually more efficient at WOT, but when the carb starts enriching the mixture (max power), efficiency drops. Thus, OK (even optimal) to accelerate briskly as long as you don't floor it and go rich. Also, don't accelerate hard just to brake at the next red light or traffic jam (obviously stupid).

If really motivated, install a wide-band O2 sensor in the exhaust, or even a simpler rich/lean indicator. Without that, you are "flying blind", unless you regularly remove the spark plugs to try to discern rich/lean and that isn't even in the same ballpark. Hardest part is welding a bung in the exhaust, though that isn't hard when reworking the exhaust. I always install 2 bungs so I can use an on/off O2 sensor to verify the wideband sensor.
 
Nah, I have lived in mountains all my life and 10 mpg is not anywhere near normal for a /6. Typical mileage drops versus the flat lands of the midwest is about 2 mpg average for mixed rural highway and interstate driving. City driving will drop it more than mountain driving.
 
It sounds like you have one major thing wrong, and one minor. The minor is that the plugs will now be all goofed up. The major is that way to much fuel is getting thru or no where near enough air. The plugs could be the cause and the symptom, but no use changing them until you know or you will have too change them again. You just need to figure out which. Start with stuff that isn't affected by lots of other things, like the air cleaner. make sure you have good clean gas, check plug wires for crossfire, if hard to start warm look to the carb. make sure you are in high gear. Check trans fluid. Feel wheels for dragging brakes. Make sure parking brake is released completely. Use a gauge to determine your vacuum, you could have a leak. Like I said though, with mileage as drastic as that you should be able to isolate the main culprit. I will assume you don't have a dozen big block heads a few brake drums and your mother in law in the trunk.
 
As stated above, check the vacumn advance for a leaky advance diaphram. When they get old they leak and don't provide any vacumn advance thus giving you poor gas mileage and performance.
 
I have barely ant vacuum on the timing side. hose looks good but not positive. any other areas to look at for the lack of vacuum? and should it be the same reading as the other side? 17-18 hg?
 
When gas in the U.S. first approached $4.00/gal my Dad
asked my parents very elderly Florida neighbor lady:

"Does the high price of gas bother you?"

and she replied:

"No......I just buy $10.00 worth....same as always".
 
Don't hook up the vacuum guage to the vacuum line to the distributor advance; that is called 'ported vacuum' and is near zero at idle. You need to chekc what is called manifold vacuum; there is usually a port on the back intake manifold runner with a hose going through the firewall; disconnect that hose and connect you vacuum guage there.
 
My 68 dart gets 21-23 mpg going 80 mph down the interstate, with 10-11 hg on the vaccum guage. It got 15 with a worn out oil burner before I did a rebuild. Is your odometer reading right?
 
Here is another question in a totally different direction. Is your speedometer accurate?
 
moe7404 said:
here is my idea. if MPG is down the first thing to check is the distributor vacuum advance. second check the cap, wires, plugs. if the cap has a vent hole next to the center tower. plug the hole with JB-weld.
Click to expand...

Explain plugging the vent hole in the cap...........
Never had an issue with that
 
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