Having a few issues with my wagon in regards to refilling the tank and the fuel gauge being all over the place.

The fuel gauge goes all over the place when I'm driving around, when I've stopped the car it returns usually to about half full. I put in about 30 litres on top of about 15 when I first got the car and it was fine, stayed at 3/4 full on the gauge for about 200km but then all of a sudden dropped to 1/4 full in about a minute of driving. Any known fuel gauge problems I should know about?

Also I went to refill as I literally had no idea how much fuel I had and wanted to fill the tank to see what I could get out of it, as I'm filling up I'm not sure If the nozzle slipped but fuel started pissing out near the part where nozzle goes in (I paint cars, I don't know these things), as if it was too full? I really have no idea, It didn't click to tell me it was full and it was slightly worrying as half of the petrol station was closed as someone in a rental truck had put petrol in it instead of diesel. No fuel leaked out at all, just came right back up which was not a cool experience. The fuel gauge know reads over the F. Any ideas? or am I just really S***house at filling up cars?

Probably best to get a potentiometer (variable resistor), hook it up to the sender wire, and check the gauge readings from zero to full.

Resistance card in the tank might be worn, giving not consistant readings.

That sounds like a legit idea, cheers I'll give it a shot,

Well better to test the gauge first - pump is a bit more involved to get out.

Wagons are notoriously hard to fill. You MUST run the petrol in slowly otherwise it will blow back all the time

as are most 'modern' cars

Oh man I'm pretty sure it blew back pretty goddamn bad on me, i could hear it draining back in but almost overflowed I had to stop about 10 seconds before the tank was full.

most 'modern' cars have the fuel inlet to 'suit' the 'unleaded' fuel. this means the NECK/FILLER are NARROW as are the fuel pump nozzle hence slow filling