MG T-ABC

So after a run up to the gas station. The water boiled. I've got a thermostat in the radiator cap that didn't indicate anything. It also didn't boil when it arrived at the station

New? If you overfill the radiator it will boil some out after it warms up and you shut off the engine, the first time. Quite often XPAG overheating caused by distributor advance not working right. Easy to check with a timing light.

If a bit of water spit out the overflow then that's normal. As the water expands from heat, some will escape especially when you first shut it down. Whatever level the water ends up at is as much as you will be able to keep in there. I'd you top it up, the same thing will happen next time. The only way to avoid this is by fitting a recovery tank, but it isn't really necessary. So long as the car stays cool you will be fine. If the water is literally boiling then you have a cooling issue. I agree with Duncan that timing and advance is the first place to look.