So the jabsco stopped pulling water again. After emptying the filters and pulling a bit of crap out of the feed pipe it still wasn’t working. This time I was pretty sure that there was a hole in one of the hoses that meant the pump was pulling in air.
So we checked this in the most obvious and grim way you can: take it apart bit by bit and try to blow through it covering one end to see if it leaks. Cue mouth full of canal water and radiator rust. Yum. We also didn’t find a leak; all pipes were fine.
After establishing that the pump impeller was still whole (and then having a minor moment of despair: Oh Jabsco!! why why why?!), we decided to put the whole thing back together part by part checking the suction at each stage by running the engine quickly. This seemed to be going fine, leading me to hope for it to be miraculously solved, even if I never knew what was wrong. Then, when the whole thing was put back together, it wouldn’t pull any water again!! Argh!
By this point the boredom of failure was well entrenched, and we gave up on our mission and decided to drive back to where we started, just around the corner. We learnt two valuable lessons on the journey back: don’t rev up the engine needlessly when the cooling isn’t working properly (especially to pretend to crash into your friends), and don’t take off the radiator cap when its overheating. Rookie errors. We didn’t actually crash into the other boat and I didn’t actually sear my face off in a explosion of boiling water.