indicator 30 with suitable markings 31 for determining the amount of coolant 13 in the tank 10 referring now to fig5 the vacuum switch 32 is shown in threaded engagement with the connector 33 and sealed against the connector 33 by the gasket 34 the switch 32 preferably of conventional design provides a warning by actuating an audio or video device not shown in the event of a malfunction such as excessive loss of coolant 13 the pressure relief valve 35 previously disclosed in my co pending application is depicted in detail in fig6 and 7 the valve preferably limits the system pressure to about 15 psig integral with the radiator cap 36 the valve 35 is actuated by a compression spring 37 when the system pressure reaches the pre set relief valve pressure in fig6 the relief valve 35 is shown in the normally closed operating condition the spring 37 is in an extended position and the seal 38 is tightly pressed against the seat 39 of the radiator 12 at the pre set relief pressure the spring 37 is compressed as shown in fig7 by pressure acting against the valve sleeve 40 and the seal 38 is displaced from the seat 39 allowing a flow.