Heater core Bypass...Looking for thoughts...
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Senior User
Joined: Mar 2020
Posts: 159
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From: Lodi, Ca
Heater core Bypass...Looking for thoughts...
I recently picked up a nice 95 f150 XLT extended can 4x4 pretty cheap....so far all issues turned our to be really simple and really cheap.
One of the issues that enabled me to negotiate a low price was that the AC was stuck on full blast cold. No heat whatsoever.
Once I bought her and got her home, I noted that the coolant line to the heater core was bypassed completely. This lead me to beleive the heater core was bad, or the blend door was bad and the bypass was a lazy way to solve the problem.
Well today, I dug in, couldn't find anything obviously wrong, so hooked the coolant lines to the heater core as they should be.
Guess what? Everything worked perfect. No leaks...all AC and Heater functions worked perfect.
So my question for all:
Why would you bypass the heater core when everything is working fine? I almost feel like thing are too good to be true with this truck...am I missing something?
Dan
One of the issues that enabled me to negotiate a low price was that the AC was stuck on full blast cold. No heat whatsoever.
Once I bought her and got her home, I noted that the coolant line to the heater core was bypassed completely. This lead me to beleive the heater core was bad, or the blend door was bad and the bypass was a lazy way to solve the problem.
Well today, I dug in, couldn't find anything obviously wrong, so hooked the coolant lines to the heater core as they should be.
Guess what? Everything worked perfect. No leaks...all AC and Heater functions worked perfect.
So my question for all:
Why would you bypass the heater core when everything is working fine? I almost feel like thing are too good to be true with this truck...am I missing something?
Dan
Lead Driver
Joined: Jul 2017
Posts: 9,600
Likes: 1,174
From: San Jose, CA
Great looking truck!
The only things that come to mind are that the PO thought there was a leak (maybe the windshield was leaking) and disconnected the heater hose to get rid of the leak without actually fixing it.
Or they did in fact fix the heater leak (did the core look new or old? Copper or aluminum?) and just never got around to re-connecting it.
Or the blend functions were not working right at one point so they were getting too much heat in the summer and no A/C maybe.
Other than that, it's just one of those mysteries!
But you'll take it, right?
Don't worry though. Something is bound to explode soon!
Paul
The only things that come to mind are that the PO thought there was a leak (maybe the windshield was leaking) and disconnected the heater hose to get rid of the leak without actually fixing it.
Or they did in fact fix the heater leak (did the core look new or old? Copper or aluminum?) and just never got around to re-connecting it.
Or the blend functions were not working right at one point so they were getting too much heat in the summer and no A/C maybe.
Other than that, it's just one of those mysteries!
But you'll take it, right?
Don't worry though. Something is bound to explode soon!
Paul
Hotshot
Joined: Jun 2015
Posts: 12,830
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Since you can replace the heater core in less than 30 minutes there really is no reason to bypass a leaking core. The blend door is operated by a cable behind the glove box. You can move the door by hand to see if it moves freely. Did you replace vacuum lines in the engine compartment? The white hose by the passenger hood hinge has been known to dry rot and crumble. That will cause issues with the system since the recirculation and air direction doors are vacuum operated.
FTE Legend
Joined: Nov 2015
Posts: 30,912
Likes: 4,123
From: Angier, NC
By blocking coolant flow to the core will make the AC colder.
I don't care how good that blend door closes off and now with years on the system any seals are gone heat still gets by.
This will make the AC work harder and not as cold.
On my 81 with AC, not working at this time, even with the temp to cold you can feel the air out the vents is warmer than the outside air.
So it has to be picking up heat from the core. This is also a known fact on the 80 - 86 trucks.
In the 80 - 86 truck area there was a post to use a vacuum bypass valve on the core so when the AC was on MAX AIR the bypass valve would bypass coolant to the core and make the AC colder.
I need to find that as this warm air is going to drive me out of the truck LOL
Nice looking truck
Dave ----
I don't care how good that blend door closes off and now with years on the system any seals are gone heat still gets by.
This will make the AC work harder and not as cold.
On my 81 with AC, not working at this time, even with the temp to cold you can feel the air out the vents is warmer than the outside air.
So it has to be picking up heat from the core. This is also a known fact on the 80 - 86 trucks.
In the 80 - 86 truck area there was a post to use a vacuum bypass valve on the core so when the AC was on MAX AIR the bypass valve would bypass coolant to the core and make the AC colder.
I need to find that as this warm air is going to drive me out of the truck LOL
Nice looking truck
Dave ----
Lead Driver
Joined: Feb 2013
Posts: 5,006
Likes: 72
From: Roseville, MN
By blocking coolant flow to the core will make the AC colder.
I don't care how good that blend door closes off and now with years on the system any seals are gone heat still gets by.
This will make the AC work harder and not as cold.
On my 81 with AC, not working at this time, even with the temp to cold you can feel the air out the vents is warmer than the outside air.
So it has to be picking up heat from the core. This is also a known fact on the 80 - 86 trucks.
In the 80 - 86 truck area there was a post to use a vacuum bypass valve on the core so when the AC was on MAX AIR the bypass valve would bypass coolant to the core and make the AC colder.
I need to find that as this warm air is going to drive me out of the truck LOL
Nice looking truck
Dave ----
I don't care how good that blend door closes off and now with years on the system any seals are gone heat still gets by.
This will make the AC work harder and not as cold.
On my 81 with AC, not working at this time, even with the temp to cold you can feel the air out the vents is warmer than the outside air.
So it has to be picking up heat from the core. This is also a known fact on the 80 - 86 trucks.
In the 80 - 86 truck area there was a post to use a vacuum bypass valve on the core so when the AC was on MAX AIR the bypass valve would bypass coolant to the core and make the AC colder.
I need to find that as this warm air is going to drive me out of the truck LOL
Nice looking truck
Dave ----
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Bypassing the heater core also allows you to not need the A/C as often because you can actually get outside temperature air through the vents instead of always heating it to some extent. It's a mod I've wanted to do to every truck I've ever owned, but I've just never got around to it. (Well, my '71 Bronco has a shut-off on the heater hose which is the stock way to regulate temp. It's a terrible way to regulate the temp, but it does let you get cool air out of the vents.)
FTE Legend
Joined: Nov 2015
Posts: 30,912
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From: Angier, NC
After being a little warmer here, windows open and the temp to low and it was blowing warm air it has to make a BIG difference.
Thing is I also use this water to heat the intake as I am running EFI exh. manifolds on my 300 so want by pass just the core not the intake.
Dave ----
Thing is I also use this water to heat the intake as I am running EFI exh. manifolds on my 300 so want by pass just the core not the intake.
Dave ----
Thread Starter
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Senior User
Joined: Mar 2020
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From: Lodi, Ca
The first thing I looked for was any sign of the core leaking inside the cab...No sign at all...
Lead Driver
Joined: Feb 2013
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From: Roseville, MN
Thread Starter
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Senior User
Joined: Mar 2020
Posts: 159
Likes: 6
From: Lodi, Ca
The only thing I actually did was peel pack the vacuum line to a good section, as the exposed section linked pretty flakey. Its possible that wasnt working, but I still don't see it moving...should you see it moving with the AC in different modes?
great responses that I appreciate! Stuff I never considered. I'm thinking of some sort of shut off valve on the coolant line for the hot summers here...anyone do that?
Dan
great responses that I appreciate! Stuff I never considered. I'm thinking of some sort of shut off valve on the coolant line for the hot summers here...anyone do that?
Dan
