Last month I flew out to IL to pickup my first 60. '83, 4 speed, 149K, original owner, original motor, in excellent shape. I drove it back to Utah, 1800 miles, in 3 days, and it was glorious. It runs and drives great. However, the mpg has dropped significantly since I picked it up. What started up around 12 mpg now averages 5mpg. The last fill up was 3.2 mpg over 19 gallons. Thoughts? I'm not leaking anything, stock tire size, pretty standard mix of highway and city driving. Elevation is about 3K' higher than where it grew up. Also, it got pretty hot on the first couple of tanks of gas. I pressure washed the radiator to clean it out and the temp is always on the bottom third of the gauge.
MPG is dropping fast...3.2mpg
- Thread starter Manchild
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Have you calibrated the odometer?
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- #3
Negative
break out your cell phone and get one of the apps that is a gps speedometer....fill tank and drive over a known measure course....fill back up. Make sure you know what size tires you have...etc.
Old school carb fed truck...benefits from tune-ups, new wires, new plugs, rebuilt carb, new fuel filter....new air filter.
Old school carb fed truck...benefits from tune-ups, new wires, new plugs, rebuilt carb, new fuel filter....new air filter.
While the odometer is critical to get accurate MPG results, I wouldn't expect it to be so erratic to cause the differences in MPGs observed. So I would suspect either engine malfunction (but you say it runs great), or fuel loss (leaking or stealing!) or drastically different driving conditions (I get much lower MPG when driving off road compared to high way driving).
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- #6
Driving conditions for the last 3 tanks have been comparable. It is parked in my garage at night, and outside my office window in the day so I'm not worried about a syphon thief. There is the occasional oil drip but no other leaks that I can see on the garage floor.
As for tracking the mileage via gps, I recorded the trip from IL and the gps only registered a +-1% variance between gps and odometer. I'm going to do a compression test and then put it up on the rack to see if anything else is going on underneath. Any other suggestions of things to check or look for? Thanks!
Check for leaks when it is running. Could there be a pin-hole leak somewhere that only leaks when pressurized? I had something like that under a strap on my fuel tank and didn't notice the leak at first. I did notice the rubber under the strap being slightly warped.
Something has to be seriously wrong for you to get 3.2mpg. Even SOA on 35s I couldn't get the fuel economy that low.
Are you sure that she runs well? That there are no issues decelerating or idling? Does the truck ever buck or seem intermittently low on power?
Check the fuel lines for leaks, from the tank all the way to the motor. In addition, take off the passenger side rear quarter trim panel (cargo area trim panel) and smell for gas inside the quarter.
Are you sure that she runs well? That there are no issues decelerating or idling? Does the truck ever buck or seem intermittently low on power?
Check the fuel lines for leaks, from the tank all the way to the motor. In addition, take off the passenger side rear quarter trim panel (cargo area trim panel) and smell for gas inside the quarter.
We recently had a fellow club member with a SBC FJ40 that had a carb issue that allowed the engine to completely fill with fuel as it sat in his garage at night. Can't remember if it was a float issue or possibly an electronic pump that wouldn't quit pumping.
This is why you should check your oil level and smell the dipstick for gas. If it reads high and smells gassy, you found your problem.
This is why you should check your oil level and smell the dipstick for gas. If it reads high and smells gassy, you found your problem.
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- #12
She runs well enough. No issues decelerating or idling. Takes a few pumps of the accelerator when starting. Nothing seems to be unusual. Power wise, I would compare it to climb hills like my 89 Toyota Pickup with a 22RE, pretty weak.
^ Or you could just clean EGR and put it back on. Clutch slipping, brakes dragging? Something is radically wrong, for sure, to get 3 MPG.
Report back with that compression test.
Report back with that compression test.
Something not right for sure. SOA on 35's with stock 3FE and I get 10ish.
You could have bought an F-16 and got that mileage....it's even a little quicker.
You're dumping fuel somewhere. How's the tailpipe look?. Are the plugs fouled rich? I'm pretty sure that situation is mechanically impossible
and still have the truck run "normal". I mean running smooth, no coughing, sputtering, lurching, hesitating, bogging, etc..?
10-14mpg and you're running a good lean to perfect mix depending on load and conditions. 3.5 MPG should give you vertical take off capabilities
You're dumping fuel somewhere. How's the tailpipe look?. Are the plugs fouled rich? I'm pretty sure that situation is mechanically impossible
and still have the truck run "normal". I mean running smooth, no coughing, sputtering, lurching, hesitating, bogging, etc..?
10-14mpg and you're running a good lean to perfect mix depending on load and conditions. 3.5 MPG should give you vertical take off capabilities
Wasn't there a thread about the mechanical fuel pump diaphragm possibly going bad and allowing fuel to leak into the crankcase - possibly a note in the FSM about such as well? Same diagnostic process that roadstr6 gave; check oil level for intermixing of fuel. Good luck, let us know what you come up with.
yes...mechanical fuel pumps can fail and dump fuel into the engine. If the fuel mileage is accurate...as described then I agree you are dumping fuel somewhere and the truck should not be running good at all. should be some obvious symptoms of running rich or fuel leaks or something at the mpg posted.