Modern Vespa

Ok so I have posted before about my gtv. We have been through a lot together and I know all of you can appreciate that.

So I would like to ask your help with a problem I am having. My fan does not kick on.

Fuses all good

Fan was replaced (probably unnecessarily)

The scooter ran with LOTS of air in coolant system for approx nine months.

When I disconnect the green temp reader/sensor the fan does not kick on like it should.

Bike is constantly overheating...

My hair is falling out.

Please let me in on any brainstorming ideas that you may be having at this moment.

Thanking you in advance

JJ

Check the fan relay is working first, and has power available to both the coil (red-white) and the contacts (grey wire). If there's power there, disconnect the blue/yellow wire from the relay coil and short that coil connection to ground. The fan should run. If it does, re-connect that wire and check what it does when the scoot is overheating - it should go to 0V - if it doesn't check at the ECU end of it.

JJ
I'm not a mechanic but if it were me, I'd do the following things.

The cooling system consist of 5 components:
1. Radiator
2. Coolant
3. Water pump
4. Thermostat
5. Fan

Make sure the coolant is full. I'd probably just use water for the first step because you may have to empty it all later if the pump and/or radiator needs service. Don't forget to put coolant in later if you fix it.

If it still overheats, I'd check the fan by connecting 12V directly to it to see if it runs.

If the fan works and it still overheats, I'd likely replace the thermostat.

If it still overheats, its either the radiator or the water pump and at that point, I'd likely take it to the dealer and let them fix it since that's more work that I'd want to do but you might want to dig in further.

Also, since you coolant dropped so low, I wonder if you have a coolant leak somewhere.

Hopefully, someone more knowledgeable than me can offer more advice.
Best
Miguel

[edit: Jimc posted while I was typing]

Thank you guys very much. Both responses were very insightful...