Volkswagen Polo turning and turning and then misfireing not sure if its the coil packs or what it is the temp gauge not working and a small crack in the pipe thatson the airbreather

Why don,t you remove the plugs and check that your getting a good spark when cranking,bear in mind there could be fuel vapour around cylinders which can ignite ,so you have to cover the holes or displace the leads away from them

Notorious for engine coolant temp sensors failing .Replace or repair pipe/ hose .