1989 Century heater problem

[ltsnow]

My heater works intermittently. When I accelerate it is hot, but when I'm idling or cruising the temperature is only luke warm. Any suggestions.

[yogi_123rd]

Sounds like the water isn't circulating properly. Most likely there's a clog in the heater core requiring flushing the system out. A less likely possibility is that the water pump is failing.