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98 Expedition heating system flow diagram #5163950 07/17/19 11:39 PM
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Fitz98 Online Content OP
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My 98 Expedition 5.4 had the heater core bypassed. I was curious if it matters which side of the heater cores the inlet and outlet hoses are connected to.
Does anyone have a diagram of the heating system flow? Looking for the hose connections from the waterpump pipe under the intake to the heater core to the aux heater pipe connections and the other hose connections from the aux heater core pipe to the front heater core to the intake.
Also looking to identify which pipes and tubes are considered inlets and outlets

Re: 98 Expedition heating system flow diagram [Re: Fitz98] #5164037 07/18/19 06:00 AM
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mk378 Offline
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Seeing a heater core bypassed you should assume that was done because the core leaks.

The hose that goes into the back of the water pump is on the suction side of the pump, it is the return from the heater core(s).

Last edited by mk378; 07/18/19 06:01 AM.
Re: 98 Expedition heating system flow diagram [Re: Fitz98] #5164042 07/18/19 06:04 AM
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Chris142 Offline
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The connection thats on the intake manifold,passenger side with the restrictor in it is the pressure side. The line going to the water pump is the suction


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Re: 98 Expedition heating system flow diagram [Re: mk378] #5164064 07/18/19 06:27 AM
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wag123 Offline
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Originally Posted by Fitz98
My 98 Expedition 5.4 had the heater core bypassed.
Originally Posted by mk378
Seeing a heater core bypassed you should assume that was done because the core leaks.
The more you dig into that rusty old Expedition, the more problems you are finding. I told you that this would happen Fitz. Good luck replacing the heater core, I think that the dash has to be removed to get to it.

Re: 98 Expedition heating system flow diagram [Re: wag123] #5164280 07/18/19 11:30 AM
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Fitz98 Online Content OP
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Originally Posted by wag123
Originally Posted by Fitz98
My 98 Expedition 5.4 had the heater core bypassed.
Originally Posted by mk378
Seeing a heater core bypassed you should assume that was done because the core leaks.
The more you dig into that rusty old Expedition, the more problems you are finding. I told you that this would happen Fitz. Good luck replacing the heater core, I think that the dash has to be removed to get to it.

I have already replaced the heater core...twice.
A huge PITA. Less of a PITA the 2nd time, since I knew the procedure, replaced all the cracked plastic dash parts while I was at it. Dash did have to come out . First time I cheaped out and used an aftermarket core. It got a pinhole leak at the tube. That is when it was bypassed by a mechanic. 2nd time was OEM and I just guessed which was inlet and outlet side. Since I am replacing the hose, I wanted to make sure I install it in the right position while it is easily accessible.
BTW, my Expedition is definitely old, but only a few rusty parts remain. Over the years, I have done minor body work, parts replacements and painting. A little at a time is easier for me financially.

Re: 98 Expedition heating system flow diagram [Re: mk378] #5164281 07/18/19 11:34 AM
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Fitz98 Online Content OP
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Originally Posted by mk378
Seeing a heater core bypassed you should assume that was done because the core leaks.

The hose that goes into the back of the water pump is on the suction side of the pump, it is the return from the heater core(s).

So would that return hose that goes to the back of the water pump also be called the outlet? The hoses online are referred as inlet and outlet.

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