Modern Vespa

I just went for a ride and, when I stopped to turn back for home, noticed the temperature gauge was resting on the bottom and not moving.

...Le sigh. Any suggestions on where to start?
I've recently listed the scooter for sale (can't afford to keep two bikes) but I don't want to pass on a problem. I had gone down a gravel road earlier in the ride, but I've ridden plenty of bumpy roads before with no issues....
Help?

I did try searching here first, but I couldn't find anything. Links to threads found by those with stronger google fu than I are also appreciated.

First thing I might check is the wire to the sender. I'm not sure but think the sender should be close to the thermostat housing on top of the engine. Could possible have come loose on the rough road.

pop the carrier under the seat and have a look for a loose wire.

As best as I can tell, nothing's unattached.

This is where it gets hard to remotely diagnose a problem.

Maybe someone with experience knows of a simple check to see if the gauge itself is working. Often there is a simple test where one grounds a wire at the sender with key on and the gauge will go to the highest reading. I would hesitate to make a guess on someones scooter.

Two other thoughts are:

Is the engine really warm? My question is if the thermostat is working allowing engine to get up to normal temperature. One wa to know if if you could take a reading at the thermostat housing with somethnig like an infrared thermometer:

https://www.harborfreight.com/infrared-thermometer-93984.html

The other idea is if the engine is in fact getting up to normal temp and the gauge and wiring to it are good then the sender may be at fault.

Please note these are just thoughts and not saying what the actual problem might be.

As already eluded to above, it's usually the sender unit that's gone faulty (most likely cause) or the temp gauge itself. With the engine hot, you could try wiggling the cables to the sender unit whilst watching the temp gauge to see if it flickers into life! Even if your thermostat is jammed fully open, your temp gauge would register some heat, so that should be ok. You can test the resistance of your temp gauge and sender unit, info on that is in your workshop manual. But ultimately, you may have to replace something if something is dead. They are not expensive units to replace.

Umm. Most of this is unknown territory for me, so I'm going to assume that means it's time for a visit to the Vespa shop?

Thanks for the responses. I think it's getting up to temperature, as it's performance isn't changed. I am worried about overheating though, since the fan kicks on semi-regularly during the warmer months and it's been mid-80's this week. I tried wiggling things after letting it warm up for a few minutes and hitting the kill switch, but nothing I noticed.

Fortuitous timing! I just noticed that Charlotte has a Vespa dealership again! I was NOT looking forward to taking the GTS across state lines and/or ordering parts and trying to bumble through this myself.
It's a sign.
I'll take the F650 down for the grand opening and to schedule an appointment, just in case the fan's operation is affected.

...Would it be affected?

Hi Cheshire, yes if the temp sender unit is faulty the fan operation will be affected.

After 3 months in the shop, I can post an update. Long story short:
Turns out the connection on the back of the instrument cluster corroded. This is what made my low fuel light stop working and, a year later, my temperature gauge stop reading.
I'm not happy that the shop didn't put batteries in the new cluster's clock (I kinda used that...) and I now have an odo in a box that reads 18,589 and an odo newly installed that's back at zero.
On the bright side, my temperature gauge works again and I'm back to riding.

Result! Ride on...

Right on ride on! (Vespa multipass.)

I take it you've decided not to sell the scoot? Or is it just taking a while to move it.

I had listed it and no one was biting, then it went into the shop because it didn't feel right to hand off my problem to someone else. While it was in the shop, events made me realize that my F650GS is a bad fit for me because of my bad leg. I was taking it out of the garage and my ankle rolled (caused by the nerve damage), which ended up with me pinned under a 450lb bike and no one around. Took 15-20 minutes to get free. No damage to the bike and only a few scrapes on my dead leg, but it almost-happens more than I'm willing to risk anymore. It's something that never happens with the Vespa.
So the BMW is about to hit craigslist and the GTS is here to stay until I can't ride her anymore.

I noticed this spring that the right foot wants to crawl a bit more than last year. Riding the Rebel I was looking down to make sure it was close enough to get the brake peddle, which had me decide this would probably be the last summer I was safe on that shifty that I really did love.
A pal saw the ad for the GTS, I quickly sent a message, test rode it the next day, wrote check and came home with the keys...
A Buick and man with his mind on marriage problems in his house crossed that center line and changed my world and ended his.... 8+years later, I want to keep on living and riding.
I think you are making the best choice for your leg and riding and hope a good sale, for your price for the other ride. Sorry the Vespa spent so long in the shop.

About that odometer....

I use an app (Road Trip) to keep up with service records, expenses, and fuel use. I spent a fair amount of time preprogramming it with all the GTS's checks and intervals.
I just found a setting that adjusts for a replacement odometer. That's a big relief for me...and changes it from a big frustration to just a little sad that my full mileage isn't shown on the bike. That, I'll get over pretty quickly, along with the clock. :shrug:

Cheshire: Just caught up with this thread, and your ordeal with the F6: YIKES!

Glad you're good after that, and very glad to know your sorted stuff out with the GTS.