Bring it in to your local auto parts store and they will test it for you for $0.
The relief vent in the radiator cap is not working, replace the radiator cap.
Check the following............................. 1. Cooling fan operation. 2. Radiator cap. 3. Thermostat.
Check coolant level Cooling fan working? Dirt or clogged radiator? Defective radiator cap?
Check coolant level Check to make sure cooling fan is working Radiator clogged? Radiator air flow restricted? Defective radiator cap? Water pump? Clutch Fan?
Bad seal Bad spring Bad neck on radiator
Check that the coolant fans are still working, then check out the water pump.
Check valve in radiator cap malfunction, replace radiator cap.
Your radiator cap is made of metal and rubber. The metal and rubber are reacting to the rust in your radiator. Rust and oxidation in your radiator will deteriorate the cap at an accelerated rate. I suggest flushing the cooling system and replacing the coolant and cap. If it persists after that you might have a heat problem that is cooking the rubber right off the radiator cap. If this is the case you should check your thermostat and heating Coil.
On a Marauder VZ800 (1998), remove the black cap (triangle shap) on the right side at the front. There you can fill radiator fluid.
Try replacing radiator cap Is cooling fan working? Make sure radiator is not plugged or dirty Check coolant level water pump
The radiator cap may be at fault.
Make sure coolant level is correct Check to see if cooling fan is working if so equipped Check radiator cap Radiator may be clogged Air flow through radiator may be restricted Water pump not working properly? Thernmostat not opening fully