Modern Vespa

Started my GTS300HPE today and almost immediately I noticed smoke coming from below the seat. Pulled out the pet carrier and there was quite a bit of smoke coming from the front of the engine bay. I looked for fire but couldn't see anything, and after 90 seconds or so the smoke disappeared. I ran the engine for another couple of minutes but apart from one or two whisps the smoke didn't return. I'm guessing it was likely a fluid leak onto a part of the engine bay that smoked as it heated up?

What colour smoke?

I'm wondering if it's a coolant leak

Grey. Here's a video

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I checked my coolant a couple of months back and it was very low. Topped it up and checked again a couple of weeks later and it was still normal. Ill check it tomorrow.

Sounds like the wiring loom shorting.



GTS 300 wiring harness burnt...again

check all your earth points are grounded properly. it could be oil on the exhaust.

I have no idea what I'm looking for as far as earth points are concerned

The wires bolted to the body create an earth back to the battery, the negative off the battery will be bolted to the body as well undo them and clean the surface up with sand paper then bolt the eyelet back on.

What did the smoke smell like? If on the sweet side - a coolant leak. If like burnt plastic - a wiring short. If like burning oil, well then it is oil seeping from somewhere. Or it could have been something caught up under the engine from the road after your last ride.

EXACTLY! They all have a very distinctive and recognizable smell.

Great, thanks I'll check it out Good question. It definitely didn't smell like burning plastic so I'll rule that out.

That's good.

If the smoke was immediate, wouldn't the engine and exhaust still be cold? Hard to imagine anything liquid hitting it would get warm enough to evaporate.

I'd lean toward electrical....

The smoke probably started 30-45 seconds or so after I fired up the engine

I definitely have a coolant leak. Checked the level and it's quite low again. The earth points look in good shape.

Due for service next month so I'll book it in and get it checked

Drip some oil after checking it recently? Oil stick is not easy to reach.

That's plenty of time for the header pipe to get hot enough to burn oil. I'd bet you have an oil leak that's dripping on the header pipe.

After I do a coolant change and start the engine, it takes 30-45 seconds for my drips to start steaming. So it is quite possibly a coolant leak near the thermostat making your "smoke".

I'm thinking high probability of a lose hose clamp causing dripping coolant onto header. I've sent this before on a couple of gts.

The low coolant level pretty much confirms it's coolant and not oil

Leave it overnight and then inspect the exhaust header and underside of the cylinder and head for dampness. Use paper towel to pat it as the dampness can be hard to see

I'd see oil under the bike too though wouldn't I?

I had a good look underneath and found a damp spot at the seal here

Firstly use paper towel to check the colour of the dampness.

Secondly, good chance that's not the origin rather it is likely that it has dribbled down to there. Check further up, all the way to the hose coming out of the thermostat. Wrap the paper towel all around the end of each hose at the clamp to see if it's leaking

Also, it might only leak when the bike is warm, so start it and warm it up for a minute or two then leave it overnight. but i wouldn't recommend riding it for now

Continue to do this checking once a day as it might take a several iterations of letting it slowly leak and then checking to determine the origin

Also, don't tighten any hose clamps **yet**. Would be good to try and identify the origin first...