This is a re-post from the GENERAL VEHICLE MODIFICATION forum, but as it may pertain specifically to a Nissan vehicle I chose to place it here as well.
I recently installed an auxiliary heater in the canopy of my 2010 Nissan Frontier. This is a simple coolant-type heater which is tied into the heater hose in the engine bay. As long as the engine is running at ~1800rpm or higher, there is excellent heat produced in both the cab and canopy. Unfortunately, when the engine idles there is not sufficient coolant flow to produce heat at either locations.
When installing the auxiliary unit, I was sure to include a bypass so I can isolate the original system from the additions. By using the bypass I get solid heat to the cab at all times - idle or high rpm. It is only when I add in the new system that I get a decrease in performance.
I assume this is due to the volume of coolant that the engine needs to circulate. Or is this caused by something else? Air lock? Restriction?
Any thoughts are appreciated. I have attached a diagram of the coolant system to assist those with questions.