Technical Why Is My MPG So Low?

sounds like the stupid modern way to me.... but I am good at math.

 

I didn't see it mentioned, but check your odometer.

Drive 20 or so miles on a road with mileposts, and compare your odometer reading to those.

A change in rear end ratio or tire size can make a significant difference from actual to indicated distance. Even a change in air pressure can make a difference, although it is very minor.

And guess I am in a minority, but MATH IS FUN! Even at my age!

Math and physics are a car enthusiast's two best friends, unless he/she is independently wealthy!

Jon

 

Pull the spark plugs, post pictures of the business end of the plugs.

 

Yes, it’s a Fordamatic.

 

The plugs have been replaced, but the engine has not had a compression test yet.

 

@'28phonebooth was asking to see the business end of the plugs to use them as a diagnostic tool, the condition of the plugs can highlight a number of engine running issues (lean, rich, poor oil sealing etc etc)

From your initial description it sounds at the very least it needs a tune up to baseline settings of ignition and carb, a compression test, then look into other areas of impact, such as poor transmission performance, dragging brakes or bearings etc.

I think expectations should be realistically set with the minding that its an old car, that could have led any sort of life before your ownership.

MPG figures whilst important to note if they suddenly change, on the whole aren't something a classic car owner should ever really be realistically concerned about. IMHO of course

 

That's assuming your odometer is accurate. If not, you can map our your route on Google maps nowadays to get a close approximation of the mileage.

 

Pencil and Paper are Traditional.

 

They are a record of the volume of fuel you purchased, important for determining mileage.

My smartphone is terrible at keeping up with my actual route unless it's active the entire time. Using an app like that could mean a low estimate on mileage.

Like you said, the MPG can indicate tuning issues or it not running as it should. While the absolute number isn't critical for a hobbyist, paying attention to it for someone less experienced can alert to when something isn't right.

It sounds like to me he has an 80-ish year old car that may not have had much engine work or maintenance. Are the rings sealing poorly? Is the thing badly in need of a tune? Can it be brought back to stock without major engine work, maybe not, but a tune and checkup on the engine might improve things or at least bring awareness to what's happening.

My cause of low fuel mileage on my cars is my foot.

 

Download a compression check app

 

I wanna like that more than just once......

 

I didn’t post this thread to be ridiculed.

 

please don't take our fun too seriously, we just like to have fun, but help folks at the same time.

 

Checked your brakes? A dragging brake plus a tired engine is a recipe for miserable fuel economy.

 

>>Download a compression check app>>
>>I didn’t post this thread to be ridiculed. >>>

No! No! It's a great idea. AliExpress has a sale on a compression check apparatus right now if you live in the US. 99¢ and free shipping. Even I can afford to get one now.

 

What is a good compression number on a flathead?

 

Funny you should ask. I just asked google's auto intelligence guy the same question. He claims "For a well-maintained, normally aspirated street flathead engine, a good compression reading should be around 130 PSI or higher per cylinder, with readings consistently within 20% of each other"

 

And when your battery dies?

 

It’s called humor.

and it helped my bumping the thread.


that’s how it works

 

I've never known how to get with the program. That's why I'm here. I prefer pre app stuff.
My dislike is based on fear and ignorance.
J/K, Jack.

 

You gotta have thick skin to hang around here brother. I’ve been insulted numerous times, but sometimes you just gotta consider the source. If you can weed through the bullshit, you will find some helpful information. Posted from my smart phone.

 

You have changed the plugs. That IS a tune up on a car with a non points distributor and no timing adjustment. A flathead with a fordomatic is NOT that.
Start with the basics. Do a full check and tuneup. This includes going into the distributor, compression check, dwell and timing set, carb adjustment and perhaps rebuild. This will confirm engine condition and optimum adjustment. Then check the rest of the drivetrain, brakes, alignment, tire pressures. All of this will affect MPG. Also understand that a 70 year old car was not designed for modern fuels, so some specs should be treated as suggestions, not absolutes. Each car will require different adjustments to run it's best due to wear, fuel, driving style and local conditions.


The reason for some humor is that this concern for MPG has been an issue for as long as people have had to pay money for fuel. It has been discussed, been the impetus for wild claims and snake oil hoaxes, been researched by DIY, independents, major manufacturers and legislated by government.

If you understand basic physics, you know that energy is used to move the vehicle and yourself, so using less to do more is a fundamental concept. Asking how is something that has been covered in the depression, during WWII with rationing, during the gas crisis, and at every time in between. It is a subject that has been covered more than the dangers of smoking. The answers are out there.

 

If you have to say it's humour, maybe it wasn't funny. That bump from 6-minutes earlier was a noble service you provided.

 

Need a humor app

 

I agree with jaracer that the centrifugal advance might not be working, especially the way the flathead distributors have the advance located under the points plate where the weights seldom get lubed, cleaned and sometimes won't move because of rust
The easy way to check is to connect a timing light to make sure timing advances during the change from low rpm to high rpm.

 

You don't need any devices other than a pencil & paper ... And your mind ..shouldn't have to hunt for that !

 

I think this car would have originally had a "Load-O-Matic" distributor. If it still does I don't think you'll find any advance weights below the breaker plate. Load-O-Matic distributors need to be used with a specific compatible carburetor that has a port that provides an air speed signal to the distributor to control ignition advance. Search the HAMB or the web for "Load-O-Matic" for more info and ways to update to a later model distributor with both mechanical and vacuum advance controls.

 

^^^^ This. The OP says the car is 'stock' but admits to not knowing much about it. An incorrect replacement carb, misconnection between the distributor and carb, there's multiple ways this could be wrong.

And I would be concerned about the poor mileage as running that rich can't be doing the rings any good with washing away the oil.

 

Could be a hundred things starting with
1) engine condition. Tune up starting with compression test. Bad compression and low oil pressure = worn out motor

2) Driving conditions

3) Your driving habits

4) General condition of car. Wheels out of line, low tire pressure, dragging brakes, and other things can drag down mileage but usually not that much.

Lots of advice in this thread, should keep you busy for a while. Hope everything works out for you.

 

If you need a bit more information about working with vintage ignition systems you might want to give this a look. Or two.


https://www.jalopyjournal.com/forum/threads/hot-rod-technical-library-basic-ignition-systems.983424/