Zuma overheating

[Just B]

First time here, kind of up a creek and would greatly appreciate any help. I have a 2018 Zuma 50 that I bought new 2 years ago from a Yamaha dealer. About a month ago the temperature light started coming on after about 2 miles or 5 minutes of around town riding at 25-30mph, which was really limiting where I can ride to obviously. I know that heat can really kill an engine and so far I’m pulling onto my street when the light comes so it’s only on for seconds but it’s every damn time, and now I've stopped completely to be safe. Here’s what I’ve done so far:

Replaced the air filter
Added just a little coolant to the overflow tank (wasn’t below the low mark to begin with)
Replaced the coolant (old coolant was clean and looked just fine)
Idled the engine with the rad cap off and burped some air bubbles out until the engine got hot then turned it off. Did this 3 separate times and by the third time there were no more bubbles.

None of that worked and I’m too far from the dealer to ride it there, plus I’d rather do it myself anyway. Some more info now – once the engine light comes on both the rad and the cap are cool to the touch, but the thermostat cover is very hot. So based on that and what I’ve read online I’m wondering is my thermostat stuck closed? I know I can get a new thermostat online and I think I’m handy enough to swap it out, but I know it could probably be other things instead or maybe in addition. If anyone has any guidance I'd love to hear it. Thanks.

[Just B]

So I took the old thermostat out and tested it and it was definitely bad. I changed that, definitely helped but the temp light still came on just took longer. Then changed the radiator cap and that make no difference. Then removed the radiator to overflow tank hose to make sure that was clear and it was. I can feel the fan running so that's not it. Starting to run out of ideas.

[sc00ter]

I'm not super liquid cooled skilled, as all the liquid cooled vehicles I've owned have been bullet proof. I would say to bring it to the dealership. They should have a flat rate for that service diagnostic. It could be a leak in the radiator not allowing it to build proper pressure. Could also be a pump failing? Radiator cap not sealing 100%? Radiator close collapsing? I'm not aware of any know issues with the Zuma 50cc 4-stroke motor. Does the oil look clean? No clouds from liquid contamination? What does the service manual suggest?

Topping up the anti-freeze a tad as you described seems o.k. to me. Wish I could have been more helpful as I came very close to buying a 50cc 4 stroke Zuma brand new. No one I know with a Honda Ruckus (another liquid cooled 4 stroke) has had cooling issues. Let us know what you find out.

[Just B]

Thanks for replying. The oil does look clean, the coolant looks clean when I'm burping bubbles out of it and no cloudiness, the radiator cap sure feels ok and I just replaced it. I actually don't have a service manual - I swear the first time I looked online I couldn't find one even for sale, though today I found a PDF at least. I'll probably do that next. I didn't have time last weekend to do anything but tomorrow I'm going to do one more round of bubble purging. I have a little hope because it definitely seemed to take a lot longer for the temp light to come on once I replaced the thermostat, so maybe now it's just air in the system? Yeah I'm a little surprised and disappointed that I'm just over 500 miles and I have all these problems.

[Just B]

So I had my scooter trucked to the dealer. Turns out the problem was a complete blockage of crystallized coolant right at the water pump, which was where I drew the line on what I thought I might be capable of doing myself. The guy said it was so bad he had to drill it out. Though I can't prove anything I guess, it's frustrating because this sure sounds to me like it was a corrosion issue caused by putting the wrong coolant in, or mixing incompatible coolants. I had the problem long before I ever added a drop of anything to the system, and even then it was just a few ounces of distilled water, followed by a full flush later on.

In total (the tow and the repair) it was about $400 for a 2 year old scooter which is aggravating. I'm just glad it's finally over and now I just hope that it's not going to be a recurring problem.

[sc00ter]

I hear ya on being unhappy at the 2 year mark! I know Honda calls for a special anti-freeze in their scooters and motorcycles, and I wonder if Yamaha does as well? I might pick-up a Honda Ruckus or a Genuine Rough House for a back-up vehicle. I'm torn between the more complicated but efficient Ruckus motor vs. the simple stinky 2-stroke. Honda will get dealer serviced, Genuine by me. And you want a good blockage story? I had a 2000 Ford Ranger, the 3.0 turtle six. Loved and looked after it since new. At 90,000 miles I started getting weird running hot issues. Had a oil change place do a Bilstein flush on the block. It clogged their filter 3 times! Inside of the block was solid rust and gunk. Ran fine after the flush but I ended up selling it. Still have no idea what caused it but I think the wrong coolant was used. I also know someone who has 60,000-I'm not kidding-miles on a Honda Metro. He has never changed the anti-freeze in it. Runs great and never gives him any issues. Glad you got the Zuma sorted out!