Modern Vespa

I just bought a GTS300 ABS and while riding it, I noticed that sometimes there is water on the floor, but I'm not sure where it comes from.
English is not my native language, I use goolge translation, sorry

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Remove the cap when it is full. Make sure the level is NOT above the top max line. Re-install the cap, and be sure it is tight. Let us know how full the level is. If it is above the max, siphon some off. Where is your temperature gauge on a long ride? Any drops on the garage floor once parked?

The fluid level is at max. I originally found that it was higher than Max, so I removed some of it. It doesn't leak when riding short distances, and it doesn't leak when parked. I don't have a water temperature meter installed, so I can't tell you the exact temperature. By the way, do you have any recommended water temperature meters?

The fluid level is at max. I originally found that it was higher than Max, so I removed some of it. It doesn't leak when riding short distances, and it doesn't leak when parked. I don't have a water temperature meter installed, so I can't tell you the exact temperature. By the way, do you have any recommended water temperature meters?

I would suggest to check the mating surfaces between the cap and the reservoir. Either there is a nick or other sort of damage (or missing o-ring in the cap), or you aren't tightening the cap enough.

Thank you, I will check if it is not tightened. I remember that the o-ring is there. I wonder if the o-ring can be replaced?

Dry everything surrounding off, and run it without the knee pad installed. Be sure the cap is tight. Keep a dry tissue in your pocket and drag it around when you stop to see if any moisture shows up. Might have been as simple as a little overfilled and the cap not perfectly tight. Leave the knee pad off until you determine beyond any doubt there is no active seepage / leak.

Thank you sir, I will try it

I know it has been a few months but damn if I didn't have this SAME problem just today. I was getting ready for a road trip and checked the fluid via looking down into the reservoir at the markings inside. I filled it to MAX, went for a ride and got the leak. Took some out, an ounce or two, then used the markings on the OUTSIDE of the reservoir, the ones that face forward to get the level a little below halfway between min/max. Cleaned everything and no leaks. A Robot trick of shining a flashlight into the opening makes it much easier to see the level. I think looking down into the inner markings made it easy to over fill.

The cap is designed to blow off at 0.9Bar/13psi and burp coolant if things get too hot and pressurized in the cooling system. Many other motorcycle systems are designed with secondary overflow bootle that catches and allows burped coolant to be sucked back in. But not on Vespas. Once in a blue moon if stuck in traffic is ok, but often I'd attribute to leaking head gasket.

Right on. Good info, thanks! My GTV and GTS are my first liquid cooled bikes so still on my learning curve

I find that in my MP3 500 the best level is at the minimum mark, at most a couple of extra millimeters. If I fill more it usually leaks some coolant (a pain in the a$$ to clean because it gets under the floorboard). Never have temperature problems and drive regularly in temperatures of 75-90 F and heavy traffic situations.

My 2012 GTV has no coolant gauge and was my first water cooled bike despite riding for 45 years! I bought it almost 2 years ago. My 2024 GTS has the gauge and here in San Diego, on the freeway, I have been one bar below the red with the fan blowing in the summer so I was a tad concerned. It does seem though that a hair over min, when over night cool, is going to be the sweet spot. That was where it was when I "topped it off" and ended up with the burping extra fluid into and onto the glovebox and floorboards. I'm headed out on my first "long distance" trip up to Big Bear tomorrow and back the next day. Keep fingers crossed for me