Modern Vespa

So I've got a strange leak that only sometimes occurs after some rides. I can't find the reason. I don't think it's oil. Here are some pics of where it's falling. I can't see where it's coming from underneath.

Any help with diagnosing would be great!!

Actually I just looked at some of the pics I took blindly with my camera pointing up and I think I can see the source of the leak. What part is this leaking?? I circled it in red

The only liquids it could be are oil, gas, coolant and final drive oil. If it isn't sweet, doesn't smell like gas and is coming from the center of the bike, my vote is for oil.

You're breaking my heart!!!!

This already feels expensive

Time to weep into my empty wallet I think.

The first two pictures look more like coolant than oil to me. See if you can catch that drip in the third picture with a clean paper towel. If it's a brown color it's oil. If it's coolant it might just be a matter of tightening or replacing a hose clamp, if you're lucky.

Ok I will do, that's good advice!!

Look for coolant leaks around the hoses where they're attached to the water pump. And look for oil dripping under the oil filter. Those places are common sources of leaks, and they're relatively easy to get to.

And check the oil and coolant levels. They may be low if the leak has been going on a long time. Even if they're not low, now you'll have a baseline in case the leaks get worse.

OK I'll try to get it on a lift or something.

You can probably see the water pump and the oil filter if you lay down on the floor.

My last picture with the red circle… what's that I'm looking at with the drip?

I'm not sure but I think it's the bottom of the engine case. The drip is probably coming from higher up. That's why I suggested looking at the water pump and oil filter first.

Search for "GTS coolant leak" and "GTS oil leak". You'll find some pictures of leaks that should help guide you.

Here's one result from searching "GTS hose clamps" that shows a leak at the water pump, and how to fix it: Question on replacing the three hose clamps

That's pretty far back and centered... that would make for a strange coolant leak.

Leaks from under the floorboard or near the radiator will come out the holes up forward on either side of the center hump. Leaks from the water pump will come out the hose connections or seals there at the pump. Leaks from the hose at the thermostat will drip through the middle of the engine and can be confusing.

Ive had all of those leaks, but yours is too far back and centered.

My guess is oil.

I stuff paper towels all around the engine (radiator hose and base gasket) as well as underneath. See what comes up wet...

Probably head gasket considering the third pic, unless it's draining there from somewhere else…

Taste it to tell if it's coolant or oil.

That. If it tastes sweet, it's coolant.

Please don't swallow

Don't forget brake fluid.

But that won't be the case here, looking at the position.

I knew someone was gonna catch that! I realized my omission right after I posted my comments.

You missed blinker fluid as well.

Place you're bets, I'm going weeping cylinder gasket, engine out.

that's likely a cylinder head or base gasket.

however, sometimes a small leak at the thermostat housing will drip down the side of the barrel and down creating the same effect. so, check the top of the motor first-- especially the hose clamp that is a known offender.

Going weeping gasket, no fluid showing other than lowest point.

while the initial does suggest a head gasket, better to inspect and evaluate.

note the witness marks from something leaking higher up. it's stained both the alum and the barrel.

two seconds and $5 for a clamp vs pulling an engine for a head gasket is a path that I'm willing to investigate.

One thing that comes to mind, should this be the head gasket at fault is that its an indication the head could be warped, don't just change the gasket without having the integrity of the head checked out.
The indication of the staining on the head has this dried due to the cylinder head temperature when run?, so why hasn't the wet patch, or has this evolved when stood, hence the patch on the floor. 🤔Interesting.
Also where the wet patch is would be down wind when the scooter is in motion so is the staining due to this ?, A small amount of oil/fluid leaking from the underneath of an engine when the vehicle is in motion spreads faster than nappy rash on a baby's butt. good luck with it😉👍.

My money is on the tstat hose. A small dribble will look like a head gasket leak.

Sprinkle some baby powder around after drying it well. The wet spot will tell the story.