Moss Motors, Ltd

Not getting any hot water flow through the heater core.  Flushed and back flushed numerous times and the flow is good and clear.  I temporarily replaced the heater hoses with clear reinforced hose to see what the water flow was doing; there was no flow!  The temp valve is functional.  Pulled the hose off the steel line which runs to the front of the motor - when running there is flow coming out of the core from the valve side, AND FLOW FROM THE STEEL PIPE!  It appears that there is a standoff within my heater core with waterflow coming in from both sides!

I've never been confronted with this issue before.  Any insight would be most appreciated.

 Thanks in advance! 

The water pump is suposed to suck water from the water valve through the heater core back to pump. Remove the water valve and make sure it is not resticting the water fllow and if it is ok there must be a pump problem.Good luck.

So as I understand your response the water flows into the core from the steel pipe (lower hose) originating at the waterpump housing, through the core and into the water valve?  Please confirm.  Water valve was removed (it was a new Moss part I replaced during the rebuild) and checked for flow - no apparent issues or restrictions.  Similar with water pump, which was also replaced as a preventative step about a year ago.  Your information on the proper direction of waterflow is valuable as there is no clear reference in the Bentley Manual which side pushes and which side pulls.  Again, if you could clarify if the water valve serves as the feed to the core or as the return, it would be helpful.  The hose from the watervalve to the core is hot when the engine is up to temperature and the hose from the core to the pipe remains cold as does the steel pipe all the way back to the waterpump housing.  I obviously have a backflow issue through one side or the other.  Any further insight?

 Many thanks! 

Not able to face the prospect of being defeated by a tractor motor I continued to work on the issue today and was successful!  Out of desperation I removed the by-pass hose at the water pump housing and discovered it was plugged solid.  What was happening was that with the by-pass plugged, rather than the heater pipe operating by venturi force and drawing water out of the heater core it was effectively functioning as a by-pass and pushing coolant to the heater core.  Only to be met by the coolant being fed through the heater valve. Stand-off solved! 

Just wanted to share the solution for the next person confronted by this problem and to thank you Tom for your quick response!