Um, 'cuz the heater core is on the passenger side?

 

Heads are universal aren't they?

 

What do you mean by that? All 7.3 Powerstroke have the return line from the heater core to the passenger head, and the pressure line coming directly from the water pump. Why would there be a line coming from the driver side is your truck plumbed like that? If so post pics I'm interested in how your engine is set up

 

I don't think anyone has a hose in the driver's side unless it's aftermarket. Both my engines just have the 1/2 plug in the driver's side head where the coolant spigot is on the passenger head.

I suppose that head could also be set up to have coolant flow through that spot. Maybe for an extra coolant filter setup or something?

 

I think what Knottyrope is saying is that you can take the passenger head off and out it on the drivers side. That heater hose connection has to go somewhere if you switch heads. That being said, it does seem a bit odd that shutting the valve off would make abig difference because the drivers side head doesn't have anything coming out of it.

Red

 

you get what I am saying

 

That was my thought.