'83 300SD heater core backflush question
 

i've got low heat output on my '83 300SD. new OEM monovalve, heater regulates as it should according to the temp wheel, just doesn't get very warm for our arctic temp winters.


today i disconnected the heater hose on the right side of the block, injection pump side, which i understand is the 'send' to the core. also disconnected the hose at the steel pipe that goes to the water pump on the left side of motor.


engine off, key off-- pushing garden hose water thru the heater hose from the water pump side of the engine, i get high back pressure. as i understand the monovalve, it should be open to flow in a unpowered state. is there a reason for the high back pressure or is my core clogged?


-dan