Overheats blows steam through resevior

[Nuwanda]

So I rebuild my waterpump with a used pump awhile back and parked it only riding it a few miles here and there for over a year. It stopped the weep hole leak. Now that I want to ride ride, it overheats and blows steam into the resevior, pushing out its coolant and the system ends up low. Initially thought air pocket and I was jot rodding to soon before being sure coolant was correct. But even after repeatedly cycling the valve and refilling and putting around for awhile, no change.The fan is not coming on and I will check the circuit. But I know steam isn't hot enough to trip the switch. The gage gets close to red, but again steam is only 212° F. No sludge in oil. No steam or white smoke from pipes. I know how to use the drain valve. Haven't pressure tested yet but I'm thinking stuck thermostat. I thought I replaced it but maybe not. Upon review, I don't think it was possible to install the impeller backwards, but at this point I'm scratching my head. Does anyone have any ideas?

 

[Nuwanda]

Oh, and to be clear; the waterpump replacement had new seals, bushing and bearing. I just used the best other parts between mine and a used one I had bought. It's parts were fine other than a hole in the case that the seller didn't tell me about.

 

[02GF74]

Let's start with the easy things.

Does it overheat when moving or when stationary or both?

Have you checked the fan works? Can test it by grounding one of the pins (check wiring diagram)

Have you checked the fan switch works? Would need to remove it and put in a saucepan of water and heat it up. Contacts close before boiling

Next test the thermostat. Again as above. Sometimes it helps to drill a small hole 3 mm, so help prevent air lock and water circulation.

If the above check out, I would suggest looking into the water pump

 

[JMax92]

No expert here, just thinking about how this sounds like the normal pressure release/hold is not working and/or bypassed.
Did you by chance open the drain tap at the base of the radiator and forget to shut it off again?
On my Gen1, that circuit looks like it allows direct flow from the bottom of the cooling system, straight to the filler cap and reservoir. That is what I think is most likely as it matches your description of events.
Good luck

 

[sdt354]

I'd bypass the fan switch and see if that makes a difference. with it running hopefully. The factory fan switch comes on too late for my liking. I put a different one in, my fan runs a lot, but I never run hot. A different, earlier opening T-stat helps too. The purging of air from the system you mentioned, so I'm assuming all the air is out of the system?