Coolant Flow Thru Heater Core

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May 10, 2005
Toronto, Canada
The heater core in my truck has coolant flowing thru it constantly since cabin heat is regulated by a trap door in the heater case. Does it help to install a ball valve in the heater core supply hose to turn off all coolant flow thru the heater core(or at least restrict the flow)during the summer months when I don't need the flow? Some heater cores are eaten away from the inside due to erosion caused by high flow. Will shutting of the flow cause problems with the circulation of coolant thru the engine?
It shouldnt, but this concern is new to me? If you flush the heater core when you flush the coolant, you should be ok. Im not certain it will "eat away the heater core" though i AM familiar with older cars that have very HOT heat from their original heater cores.. moreso than new cars.. and i do not know why that is 2cents
Many newer engines like my Jeep and the Taurus use the heater as a coolant bypass.Your 4.3 has a coolant bypass hose so blocking a heater hose wont effect coolant flow inside the engine. I do not know what effects this may have on the coolant thats sitting in the heater core.
Here is a photo of the heater hose quick-connect fittings It is in the centre of the photo, with one of the fittings being beige in color. Which leads me to ask - why do manufacturers use these troublesome fittings? These fittings have been also used on radiators, engine oil coolers and tranny coolers. The OE fittings are expensive and the cheaper aftermarket ones(like the ones that come with aftermarket rads)tend to leak. They want you to replace the o-rings in the fittings every time they are disconnected. Many fittings have come apart and blown engine oil/ ATF/coolant all over. It is so much more straight forward to just have barbs at the heater core inlet/outlet and then no new parts are needed when you disconnect the fittings. I am going to be opening up the cooling system to install a spin-on coolant filter and this is a good time to install a ball valve. I will keep it open ever so slightly in the summertime to keep the coolant fresh in the heater core.
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They use those quick connects because they go together very fast and easy on the assembly line. Taking them off later on is a different matter. I wouldn't worry about coolant flow through the heater. I think if you have no air and especially cold air blowing over the heater core, the flow through it is lower as there is less of a pressure differential between the inlet and outlet.
Here is a photo of the coolant bypass hose The bypass hose is the one partly hidden by the heater return hose. Small dia hose, I suppose not much flow is needed when the engine is still warming up.
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