Heater problem

Our heater works fine -- sometimes. It is erratic. Generally if we are driving 60 mph or less it is working; over 65 seldom and climbing a hill it often does not work. It seems to be rpm related and local mechanics have not been able to diagnose the problem. Has anyone out there experienced the same problem? Were you able to diagnose and fix the problem?

Parkman

You have a vaccuum leak! Usually, it is near the resivor under the hood mounted on the firewall. It could be the vacuum hose, check valve or the resivor itself. It is rpm related, because an engine pulls less vaccuum at higher rpm and under load conditions.