coolant diagram

jim_22

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I am looking for a coolant flow diagram for the 7.3 IDI. In particular, for the heater hose it appears to me that coolant flows though that hose, though the firewall even when the heater is off, is this true? Also which is the output from the block the higher up hose near the front (my guess) or the lower hose further back?
Thanks in advance,
Jim
 

The Warden

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This is for a 6.9l, but the flow is identical on a 7.3l. Please excuse the crudeness of the diagram, and unless you've installed one (which I would recommend), don't worry about the coolant filter shown in the diagram...your truck won't have that from the factory.

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Coolant flows from the engine block/cylinder head (the rear hose) through the heater core and back into the water pump (the front hose). And, yes, coolant DOES flow through the heater core at all times, even if the heater's off. The lever for the heater in the cab controls a flap...and there's insulation on the flap that's supposed to completely seal off the heater core if you don't want heat. However, this insulation gets old and brittle and ineffective after a while, so I would recommend installing a bypass valve on the heater hoses. The way I have mine set up, the valve will be closed if the selector lever's on "OFF" or "MAX AC", and the valve will be open at all other times.

Hope this helps some...good luck!
 

subliminal

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can you simply block off the hoses or do they have to loop around to cool the engine?
 

vegas39

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can you simply block off the hoses or do they have to loop around to cool the engine?

I think they need to loop back.
I went down to lowes last winter and spent 60 bucks on 3 brass valves and some brass plumbing and made my own bypass setup.
It's a big ugly setup but it takes care of the constant heat problem and I have ice cold a/c in the summer.
 

The Warden

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I think they need to loop back.
I went down to lowes last winter and spent 60 bucks on 3 brass valves and some brass plumbing and made my own bypass setup.
It's a big ugly setup but it takes care of the constant heat problem and I have ice cold a/c in the summer.
What he said...as I understand it, the coolant needs to loop back.

And, I have to ask...why'd you spend $60 on the manual valve setup? The vacuum-operated bypass is only about $20 at the dealer, and at least on my truck, it works VERY well...the heater hoses beyond the bypass valve are nice and cool, and I don't have to go under the hood to switch the valves when I do want heat..
 

subliminal

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on that bypass valve how does it work? where do you insert it in the system and where do you connect the vacuum? sorry for the questions im just trying to figure out an easy way to bypass the heater core. im thinking i may use 2 shutoffs and a bypass tube with 2 tees before the shutoff.
 

typ4

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you can plug the heater coolant passages. the heater just uses some coolant not all.
 

subliminal

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yea but i heard somewhere that the heads get their cooling through the heater hoses?
 

The Warden

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on that bypass valve how does it work? where do you insert it in the system and where do you connect the vacuum? sorry for the questions im just trying to figure out an easy way to bypass the heater core. im thinking i may use 2 shutoffs and a bypass tube with 2 tees before the shutoff.
On the bypass valve that I installed, it's a vacuum-operated butterfly valve. If you take a look at the crude diagram I attached to this message, you can get an idea of how it works. When the valve's in one position, coolant's routed from the bottom right to the top right and from the bottom left to the bottom right. When the valve's in the other position, coolant's routed from the bottom right to the bottom left, and from the top left to the top right.

I connected mine to the vacuum line that goes to the air recirculating door (which determines whether air's sucked from outside the truck or recirculated in the cab). I simply put in a T-fitting so that, whenever the door's closed (i.e. the system's OFF or in MAX A/C), the valve would also be closed, and the valve is open at all other times. I THINK the line's black with a white stripe, but I can't say for sure...it's right by the heater core fittings at the back of the engine compartment, and I think it's either the only vacuum line present in the area or, if not, it's the one furthest outboard.

As to whether coolant needs to loop...I quite highly doubt that simply shutting off coolant flow to the heater core will make the engine spontaneously explode ;) but I do recall some people saying in the past that it's better to let the coolant loop back to the water pump than not...and that it was under debate at the time and (AFAIK) never resolved. Frankly, I don't really know myself, but I figured it'd be better to be safe than sorry, and since the valve I used facilitated it as it was, no harm no foul, right? :) Russ is of course correct that the heads do NOT get their cooling from the heater core hoses...
 

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