Clutch material !
As long as your coolant is not dropping it sounds like its just clutch material. Time to change the clutch plates ! Pretty easy if your mechanically inclined and have the service manual.
OR
If you have to keep filling your radiator then water is getting in the oil. This can be caused by lots of things but more then likely you have a blown head gasket or warped head , this happens from over heating.
A 1967 VW beetle doesn't have a radiator you nit wit, ITS AND AIR COOLED ENGINE!!!!!!!!
lower radiator hose
Lower radiator hose.
If it is an air cooled engine then it will not have a radiator cap.
The old Beetles were air cooled, no radiator cap.
The inlet to the radiator. Hot water from the engine goes in to be cooled.
The Aprilia RS50 motorbike is a wonderful machine. It comes complete with a 50cc engine (two stroke, single cylinder, and liquid cooled). It also reaches speeds of 30MPH.
The Yamaha 850 XS is an air cooled bike. There is no radiator to fill.
The 2001 grizzly 600 ATV is "Air Cooled". There is no coolant. The little radiator in the front is an oil cooler.
I don't think this is a liquid cooled atv, meaning there will be no radiator.
A hot radiator releases excess coolant through the spring-loaded cap in to the reservoir, and when cooled the partial vacuum created by cooled radiator pulls it back in. A reservoir should be only about 1/4 full cold on a system that uses a radiator cap, some cars have a pressurized cap on reservoir and no cap on radiator
On cars that have them they are air cooled since there is no radiator.