Coolant Flow through Heater Core

[SR77]

Does coolant always flow through the heater core or is it only when the heater switch is turned on? If it doesn't always flow through, where does it get bypassed at so it doesn't flow to the heater core?

One of the reasons I am asking is because I am gonna do a complete flush of the coolant(dump the radiator and block drains) soon, but my heater is currently not working so i can't(yet) turn the heater on to flush all the coolant out. Just wondering if coolant is always flowing through the heater core, then even thought my heater is not working, this coolant will still get flushed out. thanks

 

[BarkerMan]

Some cars have the heater core active all the time, some don't. I think that most modern cars do. You will have to check with a service manual or call your dealer. Don't depend on you're dealer's answer because the people that answer the phones often don't know what's under the hood or how anything works, try several.

 

[Drew99GT]

Look at the cooling system. There's a valve on one of the heater hoses on my car that controls flow through the heater core.

 

[Kestas]

Another way to tell on a warmed-up engine is by putting your hand on each coolant hose with the heat off. If you have such a valve, one (or both) hose(s) will be cool.

 

[benjamming]

What vehicle? It does on my '94 Grand Am.

 

[artificialist]

A car can run coolant through the heater core constantly if the heat is only controlled by the blend door. Otherwise, there is a valve that varies the flow of coolant. Keep in mind that it could be hidden behinds the firewall.

 

[SR77]

thanks for the replies.

I was asking as a general question for all vehicles not knowing if all where the same, but the first car I am changing out is a 1969 Camaro. I will try the heater hose trick and if they remain cold then i am going have to find where it bypasses at. thanks

 

[Gary Allan]

Just look at the water pump. If you've got anything other than a heater hose and rad hoses attached to it, then that's the bypass hose (should be fairly short). Most SBC that I've seen have the heater hose take off of the water pump and a return to the intake somewhere (in whatever direction the flow is). You should be able to see any valve by just following the hoses to the firewall. They would probably be cabled in a 69 version of anything ..I would think. The heater core nipples stick through the firewall ..so there's typically nothing valved (besides air handling) inside.

 

[Kestas]

I suspect the heater valve to be easy to find on a 69 Camaro. One of the heater core hoses should have a small unit with a diaphragm and vacuum line coming from it. This is typical of the design for that era.