Solo Coolant Change


Solo Water Jacket

The Solo engine is possibly the only stock moped which came with a water cooled cylinder and head. It is a simple system with no radiator, no pump, no thermostat, and no hoses. It consists of a water jacket in the cylinder, a fill point, and a drain point. Without a radiator the cylinder and the head still have cooling fins. If not full of fresh coolant your engine will overheat and seize! It is difficult to get replacement parts for this motor. If you purchase a bike with this engine the first thing you should do is change this fluid.

Tools Required

  • 5mm Allen Key.
  • 4mm Allen Key.
  • A container to catch and store the old coolant.
  • Approximately 6 ounces of new, mixed coolant. Green automotive coolant works well. Mixed 50% coolant and 50% water (distilled water is recommended) for most climates.
  • A very small funnel.


  • First remove the fill plug with the 5mm Allen key. It's located on top of the cylinder head. Don't lose the copper washer! You might have to reuse it.
    Position of Fill Plug

Be aware that this may be the first time in 30 years this plug has been removed. You do not want to strip the head of this bolt. A spritz of penetrating lubricant may help. You may even have to remove the head to attack the plug from both ends with lubricant and or heat. If this is necessary you'll need to make both a new head gasket and a new base gasket. This is time consuming and if done incorrectly can result in engine damage.

  • The drain plug is located on the front of the cylinder below and to side of the exhaust. Position your container to catch the coolant once you remove the plug.
Position of Drain Plug
  • Remove the drain plug. Don't lose this copper washer either. Let the fluid drain.
  • Replace the drain plug with the copper washer. Using a new washer best. Most hardware store carry copper washers.
  • Place your funnel into the fill hole. If you can't find a funnel small enough a piece of paper rolled into a cone works.
  • Pour a little coolant into the funnel, let it drain in. Be patient. Rushing will just make a mess.
  • Continue filling until the fill plug hole stays filled. It only takes about 6 ounces. Provided you have your moped on a level surface you can't overfill it.
  • Replace the fill plug. Use a new copper washer if you can.
  • Clean up any spilled coolant. Make sure there is none left on your engine. It is extremely toxic. Some animals like the taste of coolant and will drink it if allowed! If you have to store new or used coolant make it is in a secure container.
  • Different regions have different laws regarding the disposal of coolant. Dispose of it properly.