The Stovebolt Site Forums The Shop Area Engine Shop Could a heater shut off valve overheat head?

This may be a silly question, but I've decided to bypass my damaged stock heater (coolant) valve with a cable operated one. I noticed the new one is a 100% shut off. Is it safe to cut off flow to the head until the thermostat opens? I know from experience that they like to crack.

"Is it safe to cut off flow to the head until the thermostat opens?"

What year & type engine?

If it is a 216/235/261, there is normally no flow to/through the head until the thermostat starts to open (unless you drill a hole through the thermostat plate.

Not exactly sure what you are asking. There is a hose that comes from a hot source on block/manifold and goes thru the heater core (radiates heat) and a hose back to water pump. Has nothing to do with interfering with motor/head water flow/cooling. You are not shutting off flow to the motor unless you are doing something really funky. Especially when closed 100%. It does not take very much volume away from cooling system. So, yes, it's safe and done all the time. The original valve shuts off 100% too doesn't it?

You may have been told this before but: ALWAYS say what truck, what year, what motor...........no matter what the question is.

AMEN, Hallelujah, PRAISE THE LORD (sorry about the blasphemy).

If bypassing the heater core causes overheating, something else in the heating system ain’t right.

I believe that principle would apply to nearly all years/ models/ motors.

Heaters were optional for many years. If not having coolant flowing to a heater core was damaging there would be a lot of old Chevys dead in the ditch by now.

There may be more to the OP question then most would think.
It was not until 1948 that Chevrolet introduce a bypass path in there engines to keep water flowing when the thermostat is closed.
If you look at the front of the block where the pump mounts, you will see, besides the main water transfer holes, an extra hole which only goes into the block a short distance, then turns up through the head gasket and into the head water jacket. This circulated water just through the engine and head when the thermostat was closed.
Of course this is only important on heater delete vehicles, which a lot were in those days.
Chevrolet must have added this bypass for some reason...
I do not know if an original 1947 or earlier thermostat had a small bypass designed into it, but it may have, which would accomplish the same thing.

"Of course this is only important on heater delete vehicles."

"delete"?

Since heaters were optional/accessory equipment, what was the standard "path" on standard equipment trucks in those years?

Tim, I would guess that the thermostat housing would be plugged, as well as the water pump fitting. I swear that I overheated my stovebolt on the initial startup by routing the the heater water outlet on the thermostat housing directly into the water pump housing fitting, thereby recirculating hot water from the head/block right back into the water pump inlet- not a good idea...

I could be wrong on this - but wouldn't be the first time.
I believe the heater shut off valve was used with heaters that did not have a heater control valve. The temperature was controlled by opening or closing the outlet door.
My 55 Grumman is that way and so is the 59 Bus. I realize both are "commercial" vehicles, but both operate in this manner. The only way to change the temperature is to increase/decrease fan speed and/or open or close the door.
Consequently, in order to stop hot water flowing through your heater on a hot summer day, is to use your shut off valve.

This passage gets plugged solid on some of the engines I've torn down.
Not too sure the older flapper valve thermostat sealed closed tight enough to be an issue of no built in by pass.