Hello
For my experience of magnets I use the motorcycle (K75 BMW, 750cc and 75 CV). I see a drop of 5 to 10% after 5 km. With my daily journey of 000 times 2 km urban (about 22 to 50 km / h on average, maximum speed 60 km / h) I went from 130 L / 5,5 km (sometimes up to 100 L) to 6 L / 5 km regular or even 100 L. Manufacturer's consumption 4,9 L at 4,2 km / h and 90 L at 5,6 km / h.
But to measure consumption is ultimately quite difficult it takes the same weather conditions, the same fuel, the same speed and the same driving, the same weight etc ... It will be necessary that I remove it one day to compare .
Note that I did a little "cleaning" of the supply circuit with twice a small dose of acetone and it seems that it has given a little more economy since.
For Neodymium magnets they hold well on the motorcycle, we are probably quite far from 80 ° C (this is not the curie temperature but the threshold from which they begin to permanently lose part of their magnetization). Note that there are Neodymium grades that hold more than 80 ° C, otherwise there is the Samarium Cobalt but it is much more expensive.
Assembly with stainless steel tube (0,5mm thick) air gap of about 1 mm and closing of the field to have maximum flow like André.
Michel