Ok, I'm a heating an air conditioning guy for buildings, but I am not mechanic (although, I try really hard). Can someone tell me how the coolant flow works? By that I mean, does it always flow through the heater core? And thus, when you spin the dial to some variable of heat it uses a damper to change the flow of air so that it hits the heater? Or, is that dial opening a valve that makes coolant flow through the heater core? If this was water flowing through your office building, I would have it licked; I just don't have the knowledge of how this works...unfortunately.

 

I'll start at the water pump:

Pump discharges to 3 parallel circuits: left (driver's side) bank, right (passenger side) bank, and oil cooler/EGR cooler. The oil cooler and EGR cooler are plumbed in series. All circuits come back to the crossover integral to the top of the front cover. The heater is supplied from the passenger side of the crossover, the thermostat is at the driver's side.

The heater return is T'd into the degas bottle return -- there is no check valve there.

When the thermostat is closed, the coolant travels though the bypass passage within the front cover back to the w/p inlet. When the thermostat is open, this passage is closed and coolant goes to the radiator. There is a small line off the radiator that goes to the degas bottle, the degas bottle return is back to the w/p inlet along with the heater return (see above).

The heater circuit is in parallel with the thermostat/radiator circuit. They both return to the w/p inlet, and the cycle starts again.

Some common cooling system myths:

- The water pump makes pressure. Nope. It makes flow. The resistance to that flow is what produces pressure.

- The water pump is responsible for the system pressurizing. Nope. The pressure rise measured across the pump is equal to the pressure drop of all the circuits between the pump discharge and the pump inlet. System pressure is primarily a result of thermal expansion of the coolant.

- The thermostat controls coolant temperature. Nope. It's not really a thermostat like the one on the wall of your house, it's a thermally-controlled flow distribution valve. Between its start-to-open (STO) temperature, 89C/192F on a 6L, and its full-open temperature (about 202-205F), it is true that flow is proportionally divided between the bypass and the radiator, but the actual stablilized temperature of the system is reached when the heat flux in (from engine and EGR) equals heat flux out (via radiator and heater) (Q-dot in = Q-dot out). This depends on coolant flow rate, engine load, airflow rate, and ambient temperature and the thermostat doesn't enter into it.
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i credit "autojim" from the dieselsite for this info i copied. even though i would love to look this knowledgeable

 

Good information there Raptor, to answer some of the other questions, unless you have a water control valve that is vacuum operated to block flow to the heater core(usually only found in cold climates), coolant is always flowing through the heater core. A blend door is used to direct the air flow over the heater core to create heat in the passenger area. It is easier mechanically cable controlled or vacuum actuated.

 

Thanks for the info guys.