Having problems with my 420 overheating and then shutting off. Fan doesn’t come on, temp light doesn’t come on. It happened to me this spring and I changed the thermostat and all was good. Then my rings wore out so, I put a new piston and rings in, found a crack on the headpipe exhaust bolt hole, so changed the cylinder head with a spare that I had, I transferred the thermostat from the old head to the new, now I have great compression but the bike shuts down when it gets hot and the fan won’t come on again. Tried 2different thermostats(all used but were working in the bikes they came out of), same thing. Tested the thermostats in boiling water and it opens just fine, so I thought airlock? burped and bled the system several times to no avail. Took the water pump cover off and checked it, it turns just like it should, changed the temp sensor, now I’m frustrated and don’t know what else to check. Could all 3 thermostats be bad somehow? What are the odds of that happening? I’ve got a new one on order but maybe someone will read this and know what’s going on.