referring to the drawings , wherein like reference numbers refer to like components , fig1 is a schematic perspective illustration of an engine assembly 10 that includes an internal combustion engine 11 and a chain driven component , i . e ., a balance shaft drive , indicated generally at 12 . an apparatus referred to as a chain drive tensioner assembly 14 tensions a drive chain 16 of the chain driven balance shaft drive 12 . the chain drive tensioner assembly 14 includes a tensioner body 18 and tensioner piston assembly 20 in contact with the drive chain 16 . it should be appreciated that , while the variable leakdown chain drive tensioner assembly 14 is applied to the chain driven balance shaft drive 12 , the variable leakdown chain drive tensioner assembly 14 may alternatively be applied to other chain driven components , which may include but are not limited to , chain drive components used to drive complex valve trains , oil pumps , high pressure fuel injection pumps and water pumps . fig2 is a schematic illustration of the chain drive tensioner assembly 14 of fig1 and tensioning chain 16 . the tensioner body 18 defines a bore 22 . the tensioner piston assembly 20 has a tensioner piston portion 24 and a tensioner shoe portion 26 . the bore 22 and a tensioner piston cavity 23 of the tensioner piston assembly 20 cooperate to form a hydraulic chamber 28 , which , as discussed further below , is substantially fluid - tight and , when filled with fluid ( also referred to herein as oil ), is characterized by a hydraulic stiffness that substantially prevents inward movement of the tensioner piston assembly 20 when under loading by the chain 16 . the tensioner piston portion 24 of the tensioner piston assembly 20 is installed within the bore 22 of the tensioner body 18 . a spring 30 connects the tensioner body 18 and the tensioner piston assembly 20 . hydraulic fluid is received within the chamber 28 of the tensioner body 18 from an oil supply 32 , overcoming a ball check valve 34 . when filled with hydraulic fluid , a hydraulic stiffness or tensioner reaction stiffness is created within the chamber 28 , which substantially prevents inward movement of the tensioner piston assembly 20 when under loading by the chain 16 . the oil supply 32 provides additional oil to the chamber 28 when chain loading lessens in order to replace oil that leaks from chamber 28 when under chain loading . the tensioner body 18 includes a first leakage passage 38 , also referred to as a first leakage path , in fluid communication with the chamber 28 . a leakdown disk 40 is disposed within the first leakage path 38 . the leakdown disk 40 is operable to regulate flow through the first leakage path 38 at a fixed flow rate based on pressure within the chamber 28 ( i . e ., dependent on the loading of the chain ). however , because viscosity of oil within the hydraulic chamber 28 decreases as oil temperature increases , a greater volume of oil will flow out of the first leakdown path 38 at a higher temperature ( and lower viscosity ) than at a lower temperature ( and higher viscosity ). in typical chain drive temperature assemblies having only one leakdown path , as the leakage increases , the tensioner reaction stiffness decreases and , conversely , as the leakage decreases the tensioner reaction stiffness increases . however , to compensate for the affect of increased leakage through the first leakage passage 38 as temperature increases , the valve body 18 defines a second passage 42 , also referred to as a variable flow passage or a selective leakdown path , in fluid communication with the chamber 28 . the second passage 42 is a selective leakdown path because an actuator 44 selectively blocks flow or permits flow through the second passage 42 as a function of temperature . specifically , in the chain drive tensioner assembly 14 , the actuator 44 is a thermal wax actuator that has thermal wax 46 confined within a piston cavity 48 . thermal wax motors or actuators are commercially available . the thermal wax 46 is selected based on its melting temperature in relation to the desired hydraulic stiffness of the chain drive tensioner assembly 14 . at relatively low temperatures below the thermal wax melting temperature , the thermal wax is in solid form , such as is illustrated in fig2 . thus , at a first oil temperature below the wax melting temperature , the thermal wax 46 occupies a relatively small space in the piston cavity 48 , and a movable piston 50 in contact with the wax is biased by spring 52 to a first position as shown in fig2 . in the first position of fig2 , a narrowed portion 54 of the piston 50 aligns with the second passage 42 to permit oil flow out of the chamber 28 past the piston 50 . thus , at the first oil temperature ( and at all oil temperatures below the thermal wax melting temperature ), oil leakage is permitted through both the first and second passages 38 , 42 . however , at relatively high temperatures at or above the thermal wax melting temperature , the thermal wax melts , indicated as 46 a in fig3 , expanding to occupy greater space within the piston cavity 48 and overcoming the bias of spring 52 to move the piston 50 such that the narrowed portion 54 is out of alignment with the second passage 42 and the piston 50 blocks oil flow out of the second passage 42 . thus , at a second oil temperature at or above the wax melting temperature , as indicated in fig3 , leakage is permitted only from the first passage 38 . referring to fig4 and 5 , a second embodiment of a chain drive tensioner assembly 14 a is illustrated . the chain drive tensioner assembly 14 a may be used in place of chain drive tensioner assembly 14 in the engine assembly 10 of fig1 . components of the chain drive tensioner assembly 14 a substantially identical to those of the chain drive tensioner assembly 14 are represented with identical reference numbers . in this embodiment , the actuator 44 a operable to move the piston 50 from the first position of fig4 to the second position of fig5 is a pulse width modulated actuator . the actuator 44 a is an electromechanical actuator , such as a solenoid , moving in response to an electronic control signal 56 sent along conductor wire 58 from an electronic controller 60 . the electronic controller 60 receives a sensor signal 62 from a temperature sensor 64 in communication with oil in the fluid supply 32 . the controller 60 processes the sensor signal 62 according to a stored algorithm and generates a control signal 56 corresponding to the sensed oil temperature . the sensor 64 is shown mounted in the oil supply 32 , but may be anywhere in the engine assembly where a temperature corresponding with oil temperature may be sensed , including within the chamber 28 . a power converter 68 utilizes power electronics to direct a pulse width modulated current or voltage corresponding to the control signal to a solenoid 66 within the actuator 44 a . the power electronics are connected with a power source , such as a battery ( not shown ), that supplies power converted to a pulse width modulated voltage or current by the power electronics . the solenoid 66 responds to the pulse width modulated voltage or current to cause linear movement of the piston 50 corresponding to the pulse width modulated current or voltage . the pulse width modulated actuator 44 a may be finely tuned to control movement of the piston 50 to multiple intermediate positions between the first position of fig4 and the second position of fig5 , where the thinned portion only partially aligns with the second passage 42 to control the passage 42 to partially open ( i . e ., partially blocked ) states between the open state of fig4 and the blocked ( i . e ., closed ) state of fig5 . thus , the leakage from the second passage 42 may be finely tuned in correlation with oil temperature over a range of temperatures . while the best modes for carrying out the invention have been described in detail , those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims .