Thanks for directing me to that replacement article on the monovalve Mach I have one on order. You made a good point Hunter in that it is strange that it started acting up after I did a flush on the heater core going both directions with a garden hose yes it might have stirred some gunk up and partially blocked it. I do find it very strange that the last 3 trips I made with the car heat will be on for about 13 miles and then for the remainder of my trip about 37 miles the heat is off that happens with out touching the select temp. dial at all. Yes it seems like a 10-15 min. job I will pull it out as soon as I get a chance and will let everyone know the outcome. I did read where someone put a shut off valve on the hose going into the heater and that would guarantee no heat getting into the cabin in the summer. Seems like a good thing to install just in case of monovalve failure on a hot summer day. Thanks for the good ideas.