• When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.

Horrible Mileage or ?

67Survivor!

Well-Known Member
Local time
8:11 AM
Joined
Dec 19, 2023
Messages
69
Reaction score
112
Location
Upstate NY
Happy Father's Day!
At first I thought my '67 GTX (stock 440/727) was just getting horrible mileage, right around 5Mpg. Now I'm not so sure. I stopped for fuel with the gauge reading 1/4 tank. Then I put 5 gallons in and the gauge went to 3/4. Bad sending unit giving erratic readings? :thankyou:
 
Happy Father's Day!
At first I thought my '67 GTX (stock 440/727) was just getting horrible mileage, right around 5Mpg. Now I'm not so sure. I stopped for fuel with the gauge reading 1/4 tank. Then I put 5 gallons in and the gauge went to 3/4. Bad sending unit giving erratic readings? :thankyou:
Well...sounds like it.
Simple math will solve the mpg issue....
BUT: As with Kalifornia...we have Oxygenated gasoline and it destroys naturally aspirated systems...(designed for Fuel /Injection systems) so check what type of fuel you use. And if sending unit is old..it could be faulty. You should be getting at least 12 mpg...
 
Repro Chinesium sending units do not read fuel level properly, especially in our irregularly shaped 1966-1967 tanks. The top 3/4 goes down really fast. I keep a small notebook in the console of my 1967 R/T, where I record odometer reading and gallon amount at each refill. I know that my car does about 15 mpg.(Can.), and has about a 15 gallon tank, giving me a range of 225 miles. When I hit 200 miles, I start looking for a gas station. Kind of a PITA, but I have not run out of fuel, yet.
 
Fill your tank carefully to really full, just don't over do it. Do a 50 mile no fun run then carefully refill. 66/67's are tough to fill the same amount. Dave6T4's is the best way, it removes some of the inconsistencies. Ts your speedo gears and rear gears matched.
 
Last edited:
Happy Father's Day!
At first I thought my '67 GTX (stock 440/727) was just getting horrible mileage, right around 5Mpg. Now I'm not so sure. I stopped for fuel with the gauge reading 1/4 tank. Then I put 5 gallons in and the gauge went to 3/4. Bad sending unit giving erratic readings? :thankyou:

I’m confused. Determining gas mileage has nothing to do with your sending unit.

Do what Fran said, but I’d go 150 miles. Take some spare gas with you if you think it’s a risk. 5 mpg is hard to imagine.
 
Last edited:
The fuel sending unit is supposed to measure the amount of fuel in the fuel tank and communicate the fuel level to the fuel gauge. After an approximate 50 drive, the fuel gauge showed that 1/2 tank was used. I just did the quick math, that's all. I had assumed the gauge was at least close to being accurate. I'm sure it's not.
 
The fuel sending unit is supposed to measure the amount of fuel in the fuel tank and communicate the fuel level to the fuel gauge. After an approximate 50 drive, the fuel gauge showed that 1/2 tank was used. I just did the quick math, that's all. I had assumed the gauge was at least close to being accurate. I'm sure it's not.
That whole premise is inaccurate.
Do a full- 100mi- full test.
That will tell you 3 things;
What the gauge reads at full,
What the gauge reads at 100 miles,
And what the actual fuel usage data is.
 
The only reason I keep track of my mileage is that my tank sending unit is so inaccurate. I know my car gets 15 mpg (Can.), and has a 15 Imp. Gal. tank, so I have a range of 225 miles. I have a log book where I record the fill-ups, so I will know when I have to look for a gas station. Small stretch from there to figure out mpg, after converting litres to gallons.
 
Happy Father's Day!
At first I thought my '67 GTX (stock 440/727) was just getting horrible mileage, right around 5Mpg. Now I'm not so sure. I stopped for fuel with the gauge reading 1/4 tank. Then I put 5 gallons in and the gauge went to 3/4. Bad sending unit giving erratic readings? :thankyou:
(Bypassing all the posts here) There is only one accurate way to check mileage. Fill the tank to the top and record the miles on the odometer. (make sure your speedo is accurate as well) Drive the car for X many miles, stop and fill it up to the top and record the miles on the odometer. Subtract the two for miles traveled and divide the gallons used into the miles traveled. Like, 100 miles traveled divided by 10 gallons used = 10 miles to the gallon.

If that's how you are checking your mileage, perfect. I like to see maximum mileage on mine so I fill up and head for the highway. Best mileage for me is around 55 mph and 2000rpm or less on the tach.
 
(Bypassing all the posts here) There is only one accurate way to check mileage. Fill the tank to the top and record the miles on the odometer. (make sure your speedo is accurate as well) Drive the car for X many miles, stop and fill it up to the top and record the miles on the odometer. Subtract the two for miles traveled and divide the gallons used into the miles traveled. Like, 100 miles traveled divided by 10 gallons used = 10 miles to the gallon.

If that's how you are checking your mileage, perfect. I like to see maximum mileage on mine so I fill up and head for the highway. Best mileage for me is around 55 mph and 2000rpm or less on the tach.
I haven't done the 55 mph deal since my honeymoon in 1977. Drove my first GTX from State College, PA to Myrtle Beach, S.C., and got 19 mpg. All interstate driving, 3:23 rear, Goodyear Polyglas F70x14 tires. Once we got to our destination, and saw stop and go driving, mileage turned to more realistic numbers. Consumer Reports tested a Dodge Charger R/T in 1968, and listed real world gas mileage at 9-15 mpg.
 
(Bypassing all the posts here) There is only one accurate way to check mileage. Fill the tank to the top and record the miles on the odometer. (make sure your speedo is accurate as well) Drive the car for X many miles, stop and fill it up to the top and record the miles on the odometer. Subtract the two for miles traveled and divide the gallons used into the miles traveled. Like, 100 miles traveled divided by 10 gallons used = 10 miles to the gallon.

If that's how you are checking your mileage, perfect. I like to see maximum mileage on mine so I fill up and head for the highway. Best mileage for me is around 55 mph and 2000rpm or less on the tach.
That is exactly the method I used for 300 miles.
 
Auto Transport Service
Back
Top