I have a 1992 Isuzu Amigo and the O2 sensor light has come on? The manual says if that happens it just needs to be replaced. I’m wondering if there is something more serious wrong because it seems to be eating up a lot of coolant?
That sounds like the engine may have an internal coolant leak, which gets burned, passes over the O2 sensor, and ruined it. Don’t put in a new O2 sensor until the coolant loss is fixed. To put one in without fixing the coolant leak would just ruin the new O2 sensor.
Forget the manual for a moment.
Go to an Autozone or someplace and have the code read and come back and tell us what the numbers are.
Eating up coolant?
You may have a head or intake manifold gasket leak.
Has the coolant been disappearing from the coolant reservoir steadily? If so, for how long now?