Determining Model A Gas Mileage

[Ed in Maine]

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

[ryanheacox]

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.

[WHN]

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.

[Big hammer]

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

[Patrick L.]

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.

[Kurt in NJ]

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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

[Mister Moose]

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.

[Y-Blockhead]

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.

[30 Closed Cab PU]

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/

[KGBnut]

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).

[1931 flamingo]

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.
Paul in CT

[denis4x4]

Have my own 300 gallon gravity feed tank at the house with non-ethanol gas, so I really don’t care what mileage is!

[McMimmcs]

Originally Posted by Patrick L.

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 isn’t exactly rocket science !

[Kurt in NJ]

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

[gary678*]

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.

[KGBnut]

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.

[marc silva]

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��

[TerryO]

I get 100 smiles per gallon...
TOB

[whirnot]

Just fill it to whatever level you want, 8 or 10 times. Keep track of miles, and calculate it.

[TerryH]

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.

[al's28/33]

I've tracked my '28 Phaeton with double venturi carb and I get about 14 MPG, but that's all city driving, start, stop, start, stop all short trips. I'm sure those of you who do tours would have a better number probably closer to 20-25 is my guess.

[shew01]

Originally Posted by TerryH

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.

I agree. Closing up the GAV some will yield better mileage than leaving it mostly open. It reduces carbon on the plugs as well.


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[Mister Moose]

My car drives fine with the GAV closed. In the heat of summer, you barely need it open at all, in colder temps like the 40s it wants a 1/4 turn open for the first 5 minutes.

[shew01]

Originally Posted by Mister Moose

My car drives fine with the GAV closed. In the heat of summer, you barely need it open at all, in colder temps like the 40s it wants a 1/4 turn open for the first 5 minutes.

Yup. Pretty much the same for my car after the first few minutes.


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[31Abone]

10 mpg if you are lucky with wind at your back..

[Rusty30roadster]

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I downloaded a speedometer app on my iPhone that tracks current speed and keeps an odometer. Needed this when my Speedo did not work on my 60s car, I would prop my cell phone against the windshield right in front of my face. The app did all the work for me, fill up the tank full, drive for any period of time or distance, then do the simple math when I filled the tank back to fuel again. Good luck, J

[Synchro909]

Our club runs a regular economy run. The best I have done is 30.7 miles per (imperial gallon. That's 25.6 miles per US gallon over a 100 miles test.
On my current engine (6:1 head, modified B cam and Webber carburettor), I get 27 (22.5) mpg at 53 mph. Happy with that but my Tudor has been as low as 16 mpg (13.3). Not happy with that!
While towing a 1 (US) ton camper over an average 7,000 miles tour at 50 mph, I regularly turn in about 19 (15.8) mpg. It is what it is.

[gary678*]

The "eye test" which is eyeballing your gas gauge between fills is simply inaccurate. I have done 3 accurate tests for gas mileage by filling the tank, driving on trips of 100 to175 miles plus, then filing the tank to the exact pump "automatic shut-off spot", then doing the math. Results: 20.5-21.7 MPG. My car has the standard four cylinder, 3.74 rear end, 6.1 Snyder head, and a Borg/Warner 5 speed transmission. If the test is done correctly the results will be accurate. Do not be fooled by the"eye test" or a small sample size.

[nkaminar]

The only way to measure your mileage accurately is to keep a log. Fill it to the same level each time. An easy way to do that is to insert the nozzle into the tank the same way each time and fill until it clicks off. If you are worried about spills do not fill to the top. Keep notes of how you were driving and the ignition a GAV setting, for instance on level roads at 55. After 6 months you can say with some accuracy what your mileage is and under what conditions it was the best and the worse.

[Synchro909]

Originally Posted by nkaminar

The only way to measure your mileage accurately is to keep a log. Fill it to the same level each time. An easy way to do that is to insert the nozzle into the tank the same way each time and fill until it clicks off. If you are worried about spills do not fill to the top. Keep notes of how you were driving and the ignition a GAV setting, for instance on level roads at 55. After 6 months you can say with some accuracy what your mileage is and under what conditions it was the best and the worse.

Yup and the more miles the better.

[Bob Johnson]

Here is what I did. See link below.
Bob Johnson
http://www.modelahouse.com/mileage.htm

[Herb Concord Ca]

Remember using gas with ethanol in it reduces your gas mileage. The more ethanol the lower your mileage will be.

[nkaminar]

You will get terrible mileage with straight nitro methane. You have to drill out the jets to 1/4 inch. But the car will run like a scared rabbit, for about 1/4 mile.

[shew01]

I get about 15 mpg around town and 20-21 on the backroad “highways” with a Tremec T170 four spread transmission and overdrive.


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[Brendan]

i just get gas every 100 miles

[mrmoose]

Sometimes I get gas and haven't driven anywhere. This conversation is giving me some.

[dynaflash_8]

I drove my stock 30 coupe almost daily when I first bought it. My average was always around 16 mpg

[Ivan in southeast va.]

I always tell people yeah, it's a 4 cylinder but it has big pistons.

[ETAModel]

I am averaging almost 15 MPG, mostly in town and back country roads. I plan on a highway trip soon and see what happens. I keep a log, using a "clue book" and log every trip, conditions, performance, etc. Also use the Speedbot App, which shows my route, max speed, ave speed, distance, etc.

I recently read where when Ford did MPG test on Model A's at dealers the best mileage came at under 35 MPH. But few of us now can drive that slow and not get killed.