[77newell]

On my 77 coach with 6V92 (original engine was Cummins 555) there is a single engine coolant loop that starts and returns to the engine through valves in the area of engine water pump. On mine the loop comes from the engine to the bedroom heater, then all the way to the heater at the front, then to the motoraid circuit in the hot water heater, then to water compartment heater and then back to the engine. Due to low heat availability in cold temperatures I added an electric boost pump to the circuit. Originally there was a 3-way valve just above the generator up front that could allow bypassing the from heater core in warm weather. I couldn't tell any difference from one position to the other in the summer so I eliminated it.

IN your case, since bypassing the bedroom heater resulted in better heat up front I'm guessing that there may be a restriction in or near that rear heater since that is all that changed from no heat to yes some heat. I'm guessing the rest of the circuit is fine because you were more or less satisfied after removing the rear heat core from the circuit, still I did find that the booster pump helped my coach.