Should a Dodge slant six 225 cubic inch engine get only 10.5 miles per gallon after tuneup?

No, a properly tuned Dodge slant six 225 cubic inch engine should get significantly better fuel economy than 10.5 MPG. Even considering age and condition, that's very low. A well-maintained example, even an older one, should achieve at least 15-20 MPG on the highway, and possibly more depending on driving style and vehicle weight.

10.5 MPG suggests a problem *even after* a tune-up. Possible causes include:

* Incorrect carburetor adjustment: Even after a tune-up, the carburetor might be improperly adjusted, leading to a rich fuel mixture.

* Vacuum leaks: Leaks in the intake manifold or vacuum lines can drastically affect fuel consumption.

* Ignition system problems: A faulty distributor, ignition coil, or spark plugs can cause incomplete combustion and poor fuel economy.

* Transmission issues: Problems with the transmission, such as slipping, can significantly reduce fuel efficiency.

* Faulty oxygen sensor (if equipped): If the vehicle has an oxygen sensor (less likely on older slant sixes, but possible on later models), a malfunctioning sensor can lead to poor fuel economy.

* Blocked Catalytic Converter (if equipped): A blocked catalytic converter can restrict exhaust flow, reducing engine efficiency and increasing fuel consumption.

* Driving habits: Aggressive driving (rapid acceleration, hard braking) will significantly reduce fuel economy.

A thorough inspection by a mechanic is needed to diagnose the problem. The tune-up itself might have missed something crucial, or another issue altogether is affecting the fuel economy.