All about the G10

external image G10Engine.jpg


The Geo Metro gets amazing gas mileage due in large part to its tiny 3 cylinder engine, known as the G10. Its name designates its 1.0 liter displacement. Metros in the US came standard with the G10 from 1989 until 1994. In 1995 they introduced the 4 cylinder G13 engine but the G10 was available until the end of production on 2 door models.


Standard G10s with throttle Body injection are rated 55hp, turbocharged models achieved 73 HP (designated G10T). The XFi was specially detuned for extra mileage, and was rated 49 HP..... (read more)

Except for some early models, all G10s share the same block and cylinder head. Sensors on the intake manifold and the thermostat housing changed for some generations. Early models were carbureted, but soon they upgraded to GM's throttle body injection (TBI), where one injector feeds all three cylinders. Some later models and sport models had multi-port injection (MPI), meaning one injector on each cylinder.


Most Japanese cars have interference designs, which calls for regular replacement of the timing belt to prevent costly engine damage. But the G10 valve-train is a non-interference design, which means that the open valves cannot ever hit the pistons. So if your timing belt breaks, the valves will stop but cannot come in contact with a moving piston. This prevents bent valves and damaged pistons.


These engines last a long time, and are simple to fix. When determining the health of a G10, the first order of business is a compression test. Think of this as a stethoscope for your engine. With high numbers across the board, you have a healthy engine. Any remaining problems will be related to fuel delivery or the electrical system. [is this a safe statement?] Low numbers in one or more cylinders indicates a specific problem, like a burnt valve. Low numbers across the board means the engine will need a rebuild soon.

The timing needs to be set properly - See how here.

If you have a pre-1996 Metro and the "Check Engine" light on and would like to find out why, you need to access your fuse panel and look for the diagnostic port. Insert a spare fuse into the port and then turn your key to the "ON" position. The check engine light will then blink a 2 digit code over and over. It may display more than one code also. Simply count the flashes for the code. See the codes here.

Because of its simplicity and small size, you can rebuild this engine very easily. Many of the members here have done this on their own, and there are how-to guides posted to make this even easier. It is very straightforward, even if you are not mechanically minded. We are here to help you. Here is a list of engine related threads.

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