[steve25]

I have seen this same thing, reason being pump pressure is being reduced on one bank of the motor to feed the core.

[HWYSTR455]

PSI in the heater core is the same as the rest of the system on the engine side of the t-stat.


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[HWYSTR455]

Let me rephrase, PSI will not exceed the PSI of the system on the engine side of the T-stat.

Flow is only restricted at times, if it has a cutoff valve.



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[zippy]

Originally Posted by steve25

I have seen this same thing, reason being pump pressure is being reduced on one bank of the motor to feed the core.

Pressure isn't being reduced, it's static throughout the whole system. But flow is greater in the pass head when running through the heater core. BUT, if not extracting any heat in the heater core, then the hot coolant just recirc's back to the pump inlet. Thus actually heating up, the incoming coolant from the radiator.
Hotter inlet coolant temp, will require hotter outlet coolant temp to open T stat more and flow more through the rad to counter act the heater core line heating.