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Old 11-20-2020, 09:03 AM   #1
Ed in Maine
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Default Determining Model A Gas Mileage

My car is running perfectly. It starts good, runs good and is a pleasure to drive. I decided that I was going study the gas mileage on my Victoria. It isn't as easy to do because you can't fill the Model A gas tank without the risk of spilling gas on the paint. There is also a significant fire risk to having the tank filled to the near top. I decided to use the gas tank from 1/4 to 3/4 of a full tank using the index marks on the gas gauge. While not an exact measuring tool, the errors can be averaged out with several trial runs. You can see a change in the index marks with just one or two miles of driving. I try to get the index marks perfectly adjacent to each other.


Then I went to the gas station when the tank was indicating less than 1/2 full. I added gas to the tank until the 1/2 full index marks were matched. I made note of what the gas pump starting point value was and then brought the tank up to 3/4 full with matching index marks. I recorded the amount of gas it took to go from 1/2 to 3/4. On my car (1931), the amount of gas added between 1/2 and 3/4 tank was 2.995 gallons. I would like to see if this amount of gas is the same as what you find on your cars. We might establish values for other Model A years.


Then, with the tank at an indicated 3/4 full, I drove the car as I normally do around town until the index marks matched at 1/2 full and took the miles driven and calculated my gas mileage. I was shocked! My car is only getting 7.1 miles per gallon. Next, I am going to check the tire pressures, try to be more diligent in adjusting the spark advance and use the Gas Adjusting Valve (GAV) at a more minimum setting. I will also check for any dragging brakes but I doubt this is a problem because my car starts to move on the slightest hill! Note that with the GAV open further than it needs to be, the carburetor is just dumping fuel out of the CAP Jet in the carburetor.


For those that are interested, I would like to see others report on the mileage of your cars. I would like to confirm the amount gas it takes to fill the tanks between 1/4 and 1/2, and between 1/2 and 3/4 full. What other steps can be taken to improve the mileage of our Model As. This low mileage is a nuisance on club tours. Thanks for your help, ED
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Old 11-20-2020, 09:21 AM   #2
ryanheacox
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Default Re: Determining Model A Gas Mileage

I have done the same thing but lining up the F mark on the gauge with the index mark. Ran it down to 1/4 and refilled to that same level. Mine averages between 14-18mpg it seems. I suppose it's not too bad for hilly terrain and high (45-50mph) speed driving with no O/D.


Another thought, are you sure your odometer is accurate? I know mine is very close so I'm confident in the numbers I get.
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Old 11-20-2020, 09:41 AM   #3
WHN
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Default Re: Determining Model A Gas Mileage

40 years of checking with the same car. I use a two gallon gas can.

Staying under 45 MPH, on local hilly roads, it’s always been 18-20 MPG.

Engine has less than 10,000 miles on it. Sport Coupe.

Enjoy.
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Old 11-20-2020, 10:26 AM   #4
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Default Re: Determining Model A Gas Mileage

I once got 65 mpg ! Not in an A, filled the tank at the highway, drove 90 miles, filled the tank, did the math, 65 mpg! I had a tail wind speed limit 55 mph, the cloud shadow’s where pasting me!
All auto’s get poor mileage when the engine is cold, thats one reason to have a thermostat! All auto’s get poor mileage running around town
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Old 11-20-2020, 10:58 AM   #5
Patrick L.
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Default Re: Determining Model A Gas Mileage

Figuring out fuel mileage ?

Fill tank up where you're comfortable
note odometer reading
drive car
Refill tank at some time again to a point where you're comfortable which should close as to the beginning fill up.
Check odometer reading.
Figure number of gallons vs the miles driven. It'll be close enough for government work.
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Old 11-20-2020, 11:02 AM   #6
Kurt in NJ
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Default Re: Determining Model A Gas Mileage

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On a 3000 mile trip I kept records at speeds of 50-65 I averaged 23 mpg --stock rear stock head
Lately I don't really keep track, mix of parade and back road driving but usually 5 gallons gives me 100 miles, and most times I wait till it's real empty till I add --when the gauge stops moving laying on empty
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Old 11-20-2020, 11:18 AM   #7
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Default Re: Determining Model A Gas Mileage

3 gallons is really too small a sample to get an accurate estimate. Drive the car 100 or 200 miles, keeping track of all the gas you add. On the last fill, bring the gauge to the exact mark as when you started. Now you have a decent number to go on. Or use a finely calibrated dipstick, if you want even more accuracy. The odometer test could be as simple as driving ~10 miles in a modern car you know is fairly accurate, and noting the start stop landmarks. Drive the same course in your A and see what the mileage is. Or go with a GPS mileage if you trust that.

The one time I checked my mileage on a lot of short trips I got about 15.
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Old 11-20-2020, 11:22 AM   #8
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Default Re: Determining Model A Gas Mileage

I use one of those Gas Tank Extensions you see advertised in The Restorer so the gas station nozzle auto shut-off works properly. That is my 'Full' reference.
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Old 11-20-2020, 11:33 AM   #9
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Default Re: Determining Model A Gas Mileage

As mentioned above, check speedometer accuracy. I've check MPH via google maps, a free app on my cell phone, and one of the school zone radar signs. Am fast by 4mph at 40 mph - 10%. Have also driven a 1 hr loop (or so) in my other 2 vehicles and noted the millage. Repeated the loop resetting the trip meter on the A and noting the odometer reading, and was off the same amount - 10 %. The A was reading 10% high than actual



If your A is fast enough you could check your A on an Interstate using the mile markers, just do it when/where there is not a ton of traffic.


I've also drained my tank taking the gas line off, filled it a gallon at a time using a milk jug, and marked a stick at each gallon. The marks are not linear. Especially when the tank going from 1/8th tank to empty on the gauge.


With large bias ply 16s, I get about 15-16 mpg rural driving on my late 30 CCPU at 30 -45 mph, this is with the correction factor of 10% I have 3.54 rear end, running w18 plugs, 4000 miles on a fresh rebuild (standard head, compression at 65lbs.), rebuilt carb (Zenith and Marvel, both get about same MPG), no air filter, standard trans - no Mitchell or overdrive. At this point I believe the tires are causing the low MPG, am willing to live with it. But your 7 MPG seems low.


Once you are sure your Mph/odometer is correct, look at your plugs, checking them after running 30-40 mph for a good half hour, no low speed driving. Press in the clutch, turn off the ignition, coast into a parking lot or some where safe, pull the plugs and see what the center porcelain is like, should be a tan color. Running at idle /low speeds usually causes a slightly rich condition (especially at low idle of 375 - 550 rpm), and around town stop and go - the porcelain may blacken - this is normal.


If you get a ton of black powdery substance you may need to adjust your Gav, or may need to; clean or rebuild the carb, install Renners Corner Flow tested Jets, or may need to run hotter plugs. Most vendors and some carb re-builders do not use flow tested jets, which commonly causes carbs to run rich.


If you end up having the carb rebuilt, I recommend Jim Bullock Texas - https://jmacarbs.com/
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Old 11-20-2020, 01:16 PM   #10
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Default Re: Determining Model A Gas Mileage

I think that you have two problems.

1. I agree with Moose, you have much too small a sample size.

I would want to check it over at least a few hundred miles with a variety of driving conditions. (Depending on where you are in Maine, I am assuming that you have a lot of hills.)

2. Eyeballing it on the fuel gauge is just not accurate enough.

If you are reluctant to fill to the top, perhaps try some sort of dipstick that you could clearly see perhaps 3 inches from the top. The gauge has a long arm. A fair amount of movement only registers a little on the gauge.


I have written down nearly every fill up for the last 11,000 miles (because I'm nuts). I now keep a spreadsheet on my phone. Over 11,286.4 miles I have averaged 12.30 MPG and $0.279 per mile (I told you I was nuts). My car is bone stock. The engine looks like it was rebuilt in the 50s or 60s. The head looks like it has been milled (to flatten it) just a little bit, so it is slightly higher than original compression. I do not have overdrive...but I don't know which rear end it has (one of these days I will jack it up and figure it out).
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Old 11-20-2020, 02:52 PM   #11
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Default Re: Determining Model A Gas Mileage

In the 9 plus years I had my A I never worried about mileage, when it got down to about a quarter I put another 10$ in along with a glug' glug of MMO. The 40 is a different story, dual 97's and Hi-comp heads, haven't checked but it sure uses a lot, the Chrysler hemi gets about 8 around town, 18-19 hi-way.
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Old 11-20-2020, 03:04 PM   #12
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Default Re: Determining Model A Gas Mileage

Have my own 300 gallon gravity feed tank at the house with non-ethanol gas, so I really don’t care what mileage is!
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Old 11-20-2020, 03:07 PM   #13
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Default Re: Determining Model A Gas Mileage

Quote:
Originally Posted by Patrick L. View Post
Figuring out fuel mileage ?

Fill tank up where you're comfortable
note odometer reading
drive car
Refill tank at some time again to a point where you're comfortable which should close as to the beginning fill up.
Check odometer reading.
Figure number of gallons vs the miles driven. It'll be close enough for government work.
This is about as simple as you can get! The check isnít exactly rocket science !
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Old 11-20-2020, 04:31 PM   #14
Kurt in NJ
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Default Re: Determining Model A Gas Mileage

I know many say they don't care about the mileage, that fuel cost is not the largest cost, but if the mileage is proper then the mixture and engine are properly working, low fuel mileage with too much gas in the cylinders washes lubricant from the cylinder walls, and dilute the oil reducing it's lubricating propertys
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Old 11-20-2020, 07:29 PM   #15
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Default Re: Determining Model A Gas Mileage

Using the "eye" method on the gauge is only a guess at best. I've checked mine several times with an appropriate sample size filling the tank to the brim, then refilling to the brim. On a round trip to Vermont and back on rural highways the MPG was 21+(350 miles). Locally it gets 16-17 MPG. I should also add that I have a T5 transmission and a 5.5 head.
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Old 11-20-2020, 08:14 PM   #16
KGBnut
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Default Re: Determining Model A Gas Mileage

One of the reasons that I keep track of my mileage so closely (on all my vehicles) is that a notable change in mileage will tell you that something needs attention.

I'm less concern what my mileage is...rather that it is consistent.
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Old 11-20-2020, 09:04 PM   #17
marc silva
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Default Re: Determining Model A Gas Mileage

It’s like my hot rod boat, I fill it and drive it because I love it ! If I started worrying about fuel efficiency it would spoil my enjoyment. Of course it gets me when we go on a tour and we start talking mileage and motometer temps. How do I know my motometer or yours is really accurate and as far as mileage that is what it is. Everyone has a different foot weight!��. Enjoy them for what pleasure they bring you. Just worry when your mug or wine glass or ice tea is empty��
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Old 11-20-2020, 09:16 PM   #18
TerryO
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Default Re: Determining Model A Gas Mileage

I get 100 smiles per gallon...
TOB
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Old 11-20-2020, 10:55 PM   #19
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Default Re: Determining Model A Gas Mileage

Just fill it to whatever level you want, 8 or 10 times. Keep track of miles, and calculate it.
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Old 11-21-2020, 10:38 PM   #20
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Default Re: Determining Model A Gas Mileage

I have a Town Sedan, HC head, stock tires, and a Mitchell od. Freeway driving on tours, at 60 mph, yields about 21 mpg. It town, with lots of stop and go, it drops down to around 14. I’ve found it makes a significant difference how the GAV is set. I had been leaving it 1/4 turn open, found it runs just fine at 1/8, with noticeably better mileage.
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