I think what the OP was trying to convey is that the readout went from 40 MPG to 10 MPG, not miles. Otherwise, the post makes no sense.
And we still donât know how much fuel the person had to put in the tank unless I missed that .
It filled up 10 gallons so it did actually need the gas
You had to add 10 gallons each time after a 65 mile trip ? Then this thing needs to be in a shop .
I donât believe that it is possible for the engine to consume 3 to 4 times the normal amount of fuel without the check engine light illuminating.
Something is not being figured correctly. There simply is no way for this car to get roughly 6 MPG without belching smoke, fouling plugs, and illuminating the CEL; along with polluting the O2 sensors and converter and creating a stink at the tailpipe.
If there was a fuel leak that bad then that too should be very noticeable.