Boiling coolant out of storage

G'day Folks, I have a sick motor and wanted to gauge some advice before pulling it apart.
The Background is-
Its a 2004 American Rocket with circa 40k miles on the clock,
Has not been ridden much the last couple of years and after 12 months sat idle i've pulled it out, stuck a new battery on it, Rebuilt the front shocks to change the oil and seals (and slung some progressive springs in there), fixed the oil reservoir leak and changed the oil and filters. I also topped up the coolant which was a smidge below min.
All good there.
The issue is-
When started the reservoir starts boil out of the relief pipe under the engine at around 95deg (according to my obd2 reader and app)
I've tested the coolant switch and it shows 2.45kOhms @22 deg so ok at cooler temps
I've tested the relays and it works, also swapped it and it still works
The fan never cuts in when the bike is running and i've had it up to 106 deg today with no fan cutting in. However if I use tuneecu to run a fan test then the fan spins up just fine. There are no error codes reported or stored and the bike runs just fine.
All of the pipes get hot as does the radiator so i guess the thermostat is working fine. That said they get hot long before it hits 88 deg on my ecu scanner.

Short of pulling out the temp sensor then i'm not sure what to do next, can't take it for its MoT test if it boils because they won't run it on the emmissions test or rolling road brake test if its whizzing boiling fluid out of the bottom.

Any anecdotes, suggestions or advice would be most appreciated.

12 years of ownership in, this is my first real Rocket issue, i don't seem to be able to find anything similar on the forums.

Maybe faulty radiator cap .

kipper said:

Maybe faulty radiator cap .

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Good suggestion, thanks, i will try that.

I would agree - replace the cap and go again.

Makes sense for the early boil and the cap is original factory so has had a good life. But why would the fan not kick in when the temp sensor is at 101 deg? thats whats really bothering me. I have been through all of the connections that i took off to sort the oil reservoir but all are reconnected I believe. To test i disconnected the temp sensor and got the appropriate po118 code, which went away when reconnected.

Maybe an airlock in motor too. Maybe dump and rebleed coolant?

Hope so. I will do that. Thankyou

hoopsuk said:

I've tested the coolant switch and it shows 2.45kOhms @22 deg so ok at cooler temps
I've tested the relays and it works, also swapped it and it still works
The fan never cuts in when the bike is running and i've had it up to 106 deg today with no fan cutting in. However if I use tuneecu to run a fan test then the fan spins up just fine. There

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I'm confused by what you mean with the first statement. 2.45kOhms @22 deg??? How do you know that resistance value for that temp is good? Do you have some kind of legend you can reference?

The biggest issue I see is no rad fan function. You have to find out why. Obviously it functions since you can manually activate it. I'm not sure exactly how the fan is activated but I imagine the temp sensor is monitored by the ECM which appears to ground the fan relay, turning it on, when the 101c temp is reached. Since you already swapped fan relays, check that temp sensor closely (I'm guessing it is the problem). I'm assuming that the wiring and connectors are good and plugged in properly at the sensor, relay and ECM because you can manually turn the fan on with Tune ECU.

Gregger said:

I'm confused by what you mean with the first statement. 2.45kOhms @22 deg??? How do you know that resistance value for that temp is good? Do you have some kind of legend you can reference?

The biggest issue I see is no rad fan function. You have to find out why. Obviously it functions since you can manually activate it. I'm not sure exactly how the fan is activated but I imagine the temp sensor is monitored by the ECM which appears to ground the fan relay, turning it on, when the 101c temp is reached. Since you already swapped fan relays, check that temp sensor closely (I'm guessing it is the problem). I'm assuming that the wiring and connectors are good and plugged in properly at the sensor, relay and ECM because you can manually turn the fan on with Tune ECU.

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Don't want to eliminate anything at the moment, so the next thing i was going to do before the rad cap suggestion was drain the coolant, pull the temp switch and test it in the heated up scenario with some boiling water and a control thermomenter. But the reference from the manual is as below.

hoopsuk said:

Don't want to eliminate anything at the moment, so the next thing i was going to do before the rad cap suggestion was drain the coolant, pull the temp switch and test it in the heated up scenario with some boiling water and a control thermomenter. But the reference from the manual is as below.

Click to expand...

Ah, you are referencing the service manual.... I see says the blind man... You have a reference value for a cold engine which appears to be good. Not sure if this is easier but could you keep your ohm meter on the sensor and see if the value changes as the engine runs from cold to hot? If the value doesn't change or becomes funky, you know what the problem is. Probably set a code with the sensor disconnected.