The sea strainer can be above the water line, BUT there are issues, just as you noted with bad things happening going astern. The real key is entrained air in any high spot in the system, the worst being the rubber impeller pump.
We had, new from builder, a fridge cooling pump that worked fine, until running hard and surfing the boat, the air bubbles would accumulate at the high spot, the jabsco pump, the pump would air lock and the high pressure shutdown would stop the compressor.
I fixed my issue by making a alu mount that re-oriented the pump 90 degrees, so that the discharge was higher than the intake, and lead the discharge hose away with a rise so that the air bubbles harmlessly went through the pump and have surfed the boat in big waves over 18 knots without any problems....
In your case, the plastic exhaust parts melted. Take a careful look at all the hose runs, especially if you have changed things recently, with an eye to insuring there are no 'loops' to accumulate air and airlock the system, and many jabsco type pumps have symetrical mounts (2 bolts or 4 bolts) that would allow you to adjust the pump orientation to align the discharge upward (best) or at least horizontally to shed air, and your problem astern should be solved.
Another thing you might want to consider is a no flow alarm for the engine, we have them on both the main and genset, so we get visual and audible warning if water flow is impeded (plastic bag, jellyfish, kelp knob....ask me why I know this.....)
a very solvable problem, even if you need to temporarily put clear hose on the system so that you can see what is going on
very best of luck...
Originally Posted by seaescape
Hi guys. I've had a look at my strainer as osirissailing mentioned. The water doesn't come into the boat as the strainer is about 12 inches or more above the water line.
Is this correct or should the strainer be on the water line?
It seems to me that if it was lower the pump would always have a head of water to draw on and if the intake hosing from the thru hull is clear I should never have this problem.
On the Muir. I contacted them and I can buy any part of the motor or gearbox I need but they haven't gave me any pricing as yet. So I hope to repair it and still have some change in my pocket.