Heater Core Bypass - Diesel Forum - TheDieselStop.com
'99 & up 7.3L Power Stroke Engine and Drivetrain Discussion of the '99 & up 7.3L Power Stroke diesel engine and drivetrain in the 1999-Up Super Duty trucks and Excursions. No gas engine discussion allowed except on transmissions and drivetrain that pertain to all models. Please confine discussion of topics in this forum to those items that are specific to the 7.3L Power Stroke engine.

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post #1 of 16 (permalink) Old 06-28-2005, 05:14 PM Thread Starter
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Heater Core Bypass

I have a 2001 and the a/c works very good on Max cool but not good at all on bilevel. From reading here I believe that the heater core flows all the time except for when in the Max Cool mode. If this is true is it alright to put a hand valve inline with the heater hose so I can keep it shut off during the hot months? If this is alright which hose should I put the valve on?

thanks for your help
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post #2 of 16 (permalink) Old 06-28-2005, 06:21 PM
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Re: Heater Core Bypass

You can put the valve in line on the hot side of the hose from the water pump. However you will defeat the purpose of the small amount of coolant that flows to the heater core when the heat is shut off. People complained loudly when the first cold snap hits and they turned the heat on only to find hot coolant all over the passenger floorboard leaking from the heater core that rotted out during the summer. The small constant flow keeps fresh coolant with the anti-corrosion additives moving through your heater.

The better solution is the automatic shutoff valve from a sponsor dieselsite.com (Bob Riley) that totally shuts off the water during the Max AC cycle for a quick cool down. When you set back the control to regular AC the coolant flow resumes saving your heater core. You won't spend much more money and you can install it and never touch it again. Imagine a cold morning and your halfway to work freezing from no heat because you forgot to open the manual valve before leaving home. [img]/ubbthreads/images/graemlins/laugh.gif[/img] [img]/ubbthreads/images/graemlins/laugh.gif[/img] [img]/ubbthreads/images/graemlins/laugh.gif[/img] [img]/ubbthreads/images/graemlins/laugh.gif[/img] [img]/ubbthreads/images/graemlins/laugh.gif[/img]


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post #3 of 16 (permalink) Old 06-28-2005, 10:32 PM
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Re: Heater Core Bypass

www.forgotton.net/diesel/heaterbypass/index.htm

Click that. Shows you the valve, and where to put it.

As to triggering it, You can "T" into the vacuum lines in the cab so that you can select when its on or off, or in my case, I just put a "T" in right off the vacuum bottle so its ALWAYS closed. Then, when it cools off, I'll put a cap on the line to OPEN it back up.

Lots of ways to do it, but the core piece is that vacuum actuated return valve.
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post #4 of 16 (permalink) Old 06-29-2005, 02:03 PM
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Re: Heater Core Bypass

Oliver,
I did the same as Ford-Forgotton but for the vacumn I tapped into the red vacumn line that's behind the glove box. The red line has vacumn in all control settings except for "floor", "floor/defrost" and "defrost". This way I only have heat from the floor and defrosters, the hot water is shut off to the heater core in all other positions. Best compromise I could find.

I think what Bulldog sez about the stagnat water in the core has some merit. I guess I should just turn the control to "floor" occasionaly and let some water churn thru the core. Maybe that would prevent the corrosion etc.

Jim

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post #5 of 16 (permalink) Old 06-29-2005, 02:57 PM
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Re: Heater Core Bypass

I think the coolant flows through the heater core all the time. It may have reduced flow depending on the temperature control position. I almost never take mine off of max A/C. If it's a little cool, I regulate it with the temperature control and it makes the air warm.

Ray

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post #6 of 16 (permalink) Old 06-29-2005, 03:20 PM
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Re: Heater Core Bypass

[ QUOTE ]
I think the coolant flows through the heater core all the time. It may have reduced flow depending on the temperature control position. I almost never take mine off of max A/C. If it's a little cool, I regulate it with the temperature control and it makes the air warm.

Ray

[/ QUOTE ]

The heater core DOES flow all the time, however there is a "blend door" that directs airflow thru the heater core before it reaches the cabin. In MAX AC, the blend door is mostly closed, however by adjusting the "heat" setting, you can get hot air, even in MAX AC mode.

The valve that I bought is not a 100% sealed cutoff. It does pass a VERY little bit of coolant even in bypass mode. However, not enough to warm the core up by any means.

Also, I believe our heater cores are Phenolic (spelling?) and I dont think the corrosion issue is as big a concern.
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post #7 of 16 (permalink) Old 06-29-2005, 03:30 PM
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Re: Heater Core Bypass

The stock heater valve has a small round hole in it(1/4" or so). When the valve is closed in the summer a small amount of coolant can flow through the heater core. The engineers at ford are trying to help the heater cores last longer with fresh fluid flowing constantly.

Max AC is recirculated inside air. When the interior cools down I put mine back to normal AC to get fresh air coming into the cab plus the fan noise is quieter. At one time Ford had a warning in the owner's manual about leaving AC in the MAX position. As well when you park the truck the AC switch needs to be in the vent or normal AC position to allow the cab to "breath" as the cab heats and cools from the daily outside temp changes. I have read that in the desert heat you can break windows from the heat buildup and air expansion in the cab. [img]/ubbthreads/images/graemlins/eek.gif[/img] [img]/ubbthreads/images/graemlins/eek.gif[/img] [img]/ubbthreads/images/graemlins/eek.gif[/img]

Any you Arizona guys who can confirm this?


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post #8 of 16 (permalink) Old 06-29-2005, 03:51 PM
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Re: Heater Core Bypass

I've heard the same thing about putting the A/C control in normal or vent to keep temps down while the vehicle is sitting. I don't know if it's true or not because in FL it's pretty hot inside no matter what. I do put my A/C control in normal when I'm parked in the sun for an extended period; can't hurt.

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post #9 of 16 (permalink) Old 06-29-2005, 04:55 PM
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Re: Heater Core Bypass

Ford_Forgotten

I may be using some outdated information on this. I was describing systems I had worked on the past regarding the stock heater core coolant shutoff valve and the reasoning for such a design. I (thank God) have not pulled my heater core out. I went looking for the SD stock coolant valve but could not find one on the truck or in the parts breakdown. I found the blend air valve design in a parts breakdown. I've seen heater cores with plastic end caps like the radiator have but not plastic core elements. The old ones were brass/copper then aluminum then aluminum with plastic ends. I saw a new one on ebay for a 1999 F series that appeared to have brass ends and aluminum core. Things change though. Thanks for the update, you younger guys!

I do like Bob's heater core shutoff I've had mine on for several years now. They do work great! My Max AC can blow 36-38 degree air when it's near 90 as it has been lately. I keep a thermometer in my vent at all times so I can look at the temp. God I love gauges!


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post #10 of 16 (permalink) Old 06-30-2005, 04:48 PM Thread Starter
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Re: Heater Core Bypass

When my cab cools down with Max cool I will try to turn it to a/c or bi-level (which is what I prefer) and the cab warms back up pretty good. It seems to cool better in the non-max mode when I am sitting still or moving less than 60 to 70 mph. On Max the a/c seems really good but maybe it should work better than it is in a/c and bi-level even with the heater core flowing? So maybe there is a different problem?
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post #11 of 16 (permalink) Old 06-30-2005, 10:02 PM
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Re: Heater Core Bypass

[ QUOTE ]
I have read that in the desert heat you can break windows from the heat buildup and air expansion in the cab. [img]/ubbthreads/images/graemlins/eek.gif[/img] [img]/ubbthreads/images/graemlins/eek.gif[/img] [img]/ubbthreads/images/graemlins/eek.gif[/img]

Any you Arizona guys who can confirm this?

[/ QUOTE ]
Impossible. Two large air vents on the back of the cab.

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post #12 of 16 (permalink) Old 07-01-2005, 06:39 PM
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Re: Heater Core Bypass

[ QUOTE ]
[ QUOTE ]
I have read that in the desert heat you can break windows from the heat buildup and air expansion in the cab. [img]/ubbthreads/images/graemlins/eek.gif[/img] [img]/ubbthreads/images/graemlins/eek.gif[/img] [img]/ubbthreads/images/graemlins/eek.gif[/img]

Any you Arizona guys who can confirm this?

[/ QUOTE ]
Impossible. Two large air vents on the back of the cab.

[/ QUOTE ]

The air expansion doesnt break the glass.. its usually the heat expansion rate of the glass vs the steel if the glass is a little ill-fitting in the chassis.

The only other time I've seen glass break here is during the sand/dust storms during monsoon season from drastic barometric pressure changes and the wind from microbursts. Pretty wild.

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post #13 of 16 (permalink) Old 07-01-2005, 07:01 PM
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Re: Heater Core Bypass

I bought a shut off T from NAPA and was going to install it on the heater hose that comes off the head. I think that is the intake for the heater core

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post #14 of 16 (permalink) Old 07-01-2005, 07:07 PM
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Re: Heater Core Bypass

I did the brass "Ball valve", and have it installed right above the passenger side CAC tube.
I DID notice a difference with it off,,,for the AC. Thats for sure [img]/ubbthreads/images/graemlins/biggrin.gif[/img]

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post #15 of 16 (permalink) Old 07-02-2005, 10:12 PM
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Re: Heater Core Bypass

Change your coolant to waterless Evans and let all of your corrosion concerns go away along with stressing hoses and gaskets with high pressures. Just a thought.... [img]/ubbthreads/images/graemlins/smile.gif[/img]

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