Modern Vespa

I have searched but nothing jumping out to help me so....

Where exactly is the Vespa GTS 300 temperature switch for a 2017 ABS/ASR model that gets the fan running? Can one short the plug?

I have never heard the fan running but I do have a leg covering.
Radiators do heat up because it gets hot under the leg covering so I guess thermostat must be working.

Fan blades move.

Also the filler cap weeps a tiny amount of coolant that collects on a paper rag I put there.

On my car, using an ECU plugin - the temps tend to hover around 80c, and can go up to 90c in very heavy traffic. Only when the coolant reaches over 100c does the fan kick in, and it's extremely rare for this to happen.

With UK temps, and the fact it's only a 278cc, I wouldn't expect to see the fan on very often, if at all. In Italy, with 40c+ Summers, maybe the fan comes on a bit more...

Are you concerned the fan is broken, or are you looking to turn on the fan manually to heat your legs?

JakeM, Worried the fan is not coming on and maybe temp sensor is faulty.
Warm enough without the fan as Radiators are definitely radiating under the leg cover!

Have a read here. Seems it has to hit 105 Celsius before the fan activates, which takes 10-12 minutes of idling in the same position - so unlikely to happen! Vespa GTS 300 cooling fan question FIXED

The fan is more of an emergency fail safe, rather than a day to day function.

The Primavera / Sprint engines at 125cc and 155cc don't even have coolant and a radiator. They're solely air cooled.

Water cooling is perhaps a bit overkill on such a small unstressed engine.

I'm also a little concerned about the slight coolant leak at the filler cap. Its not a lot but as I said the paper rag gets moist.

No ideas on how to bypass to test the radiator fan to come on or to test temp sensor?

I don't believe Piaggio is using anything tricky like PWM for powering fans. You can probably unplug the connection from the thermo fan switch and jumper the two connectors. Fan should come on then.

For testing the fan switch, I'd measure resistance across the switch terminals with the engine cold, e.g. left overnight. Once you have the resistance value, fire it up and let it idle for 7-10 minutes. Measure resistance across the switch terminals then. Compare your observed resistance values with what the service manual lists. If it's out of range, drain the coolant and replace the thermo fan switch.

On the 300, there is no 'fan switch' - there is a relay, controlled by the ECU. There are two temperature sensors in the same 'package' - one feeds the ECU and thus the fan, the other just the gauge in the dash.

To test the fan, you can remove the fan relay, and short out 30 to 87. 30 is unswitched +12V, fed through fuse 5, which also feeds the saddle opener and the headlight relay.

Gotcha. I'll be mindful of that when I get to work on my GTS.

Is the sensor for the ECU is still a thermistor though?

Yes. The two sensors are identical.

Had to let my 2018 GTS idle a good 15-20 minutes in the sun on a warm day to get my cooling fan to come on (for testing purposes after changing coolant.)
Have had my GTS for almost a year, the cooling fan has came on only once organically, was a very hot day and was stuck in stop and go traffic.

Thanks jimc

Ok I removed relay shorted 30-87 and fan worked. Excellent. Next step....

Now I guess I need to swap relay from Fan to Headlight and see if headlight still works to rule out relay?

Then on to temperature sensor. Only thing is I cant seem to remove the connector!! Can I back probe or does connector need to be removed to test resistance? What resistance am I looking for cold and warmed up?

Same here 2013 GTS 300 and the only time the fan comes on is when changing coolant and testing/bleeding after , You really have to idle long time to force it to come on , In 10 years it's never come on in normal use !

I have to ask - have you any evidence at all of overheating? If the gauge hasn't ever neared the maximum, then the fan won't have ever come on anyway. It's very unlikely both temp sensors would have failed in the same way - and I've never heard of one actually failing anyway. If the temp gauge on the dash is operating normally then I'd very strongly suspect the sensor feeding the ECU is fine as well.

The filler cap weeping is almost certainly down to a raised seam on the tank or defective seal in the cap along with an over-filled tank - if it was a head gasket problem you'd have seen steam.

I generally don't hear the GTS fan under normal circumstances, especially in cooler weather. But I can reliably get it to come on by doing a long, multi-mile run at freeway speeds, and then exiting the freeway and idling. This usually happens at the first long stoplight after getting off the freeway.

At freeway speeds, there's plenty of air flowing through the radiators to keep the temperature down, but also plenty of heat saturation in the engine. Once you start idling with that much heat saturation (thus depriving the radiators of free air) the fan will switch on.

Hope that helps.

Okay thanks jimc. I'm going to remain cool-ant about the fan not coming on and let the radiators just radiate without the need for the fan. Appreciate everyone's comments.

yup abut heat soak and plenty of airflow at high speed

although the definition of normal circumstances is variable. some people will commute by hoping on a freeway for 30mins then get off into stop go traffic for another 20mins in mid summer -> maybe fan.

Yeah, and definitely depends how hard they are working the engine.

I tend to have the throttle pinned, so...

Like someone said. Let it tick over. For a while. Will come on

here is where the switch is : https://www.parts-piaggio.com/vespa-scooters/300-VESPA-SCOOTER/GTS/2017/GTS-300-ie-ABS-E4/Engine/Head-unit--Valve/1322/26/1022/2871