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Username Post: Heater core by pass        (Topic#355782)
gchemist 
Senior Chevytalk Moderator
Posts: 24893
gchemist
Loc: Austin, TX 78748
Reg: 05-09-00
03-26-19 01:38 PM - Post#2762952    

Anyone have their heater core by passed? I'm thinking of by passing mine. I don't need the heater heat very often. The cab sure does get HOT in Texas. However, I think the flap is partially open too. The lever won't go all the way left. A/C would work better too.

Anyone have a picture? There are several ways to by pass the core.

'83 Silverardo XST - ZZ4 powered
'95 Jimmy SLT (Bought @131,814)
'96 GMC Jimmy LS Ret. @236651 miles


 
Lead sled 
Frequent Contributor
Posts: 1945
Lead sled
Age: 59
Loc: Walton,NY.
Reg: 11-04-09
03-26-19 07:00 PM - Post#2762961    
    In response to gchemist

I just pulled the hoses off the heater core,then coupled them together with a nipple. Left the hoses connected to the water pump Worked for me

Late yr model (Dec. 51 BelAir/ 52 trim), with a basically stock 67 Camaro SS350/295hp Turbo Fire Edelbrock 1405, Saginaw 4spd/355 geared 55/6 Chevy rear.2,1st place,and 1 top five award trophies so far
http://www.picturetrail.com/bris51deluxe


 
gchemist 
Senior Chevytalk Moderator
Posts: 24893
gchemist
Loc: Austin, TX 78748
Reg: 05-09-00
03-27-19 04:17 AM - Post#2762981    
    In response to Lead sled

Yup, that works. Did the same bypass on my '96 Jimmy once. I towed an empty enclosed trailer several hundred miles to help a friend move. A day before coming back, the core leaked into the cab. Luckily, I had my trusty old metal Craftsman tool box. In it, I had a small pipe that fit both hoses perfectly. I connected them together and drove home with it bypassed.

How did you cover the core connections?

'83 Silverardo XST - ZZ4 powered
'95 Jimmy SLT (Bought @131,814)
'96 GMC Jimmy LS Ret. @236651 miles


 
Lead sled 
Frequent Contributor
Posts: 1945
Lead sled
Age: 59
Loc: Walton,NY.
Reg: 11-04-09
03-27-19 11:05 AM - Post#2763009    
    In response to gchemist

Good ol duct tape...What else?

Late yr model (Dec. 51 BelAir/ 52 trim), with a basically stock 67 Camaro SS350/295hp Turbo Fire Edelbrock 1405, Saginaw 4spd/355 geared 55/6 Chevy rear.2,1st place,and 1 top five award trophies so far
http://www.picturetrail.com/bris51deluxe


 
1983G20Van 
Super Senior Member
Posts: 3767

Loc: Bedford, Texas, USA
Reg: 11-13-02
04-01-19 03:43 PM - Post#2763425    
    In response to gchemist

Just put a ball valve in the inlet hose between the heater core and the intake manifold to shut off the hot water when you don't need heat. I have done that on practically every vehicle I have owned that did not have an actual heater shut-off valve. When you need heat to defog the windows its only a matter of popping the hood and twisting open the valve.

1983 G20 Van, 350 TPI, Ported 906 Vortecs, Edelbrock 3817 Base, ASM oversize runners. Reed Custom Roller cam, 700r4, 12 bolt with 3.08 gears, Doug Thorley Tri-Y headers, true duals


Edited by 1983G20Van on 04-01-19 03:43 PM. Reason for edit: No reason given.

 
gchemist 
Senior Chevytalk Moderator
Posts: 24893
gchemist
Loc: Austin, TX 78748
Reg: 05-09-00
04-02-19 04:31 AM - Post#2763467    
    In response to 1983G20Van

On my next run to HD, I'll look for a hot water ball valve.
Maybe two. Anyone remember the ID for hoses?

Needing defrost this morning, it took a long time for it to defrost a little frost. I need to check the flap cables. Something is not working right. Plus, I hear a vac leak behind the controls. Right now, BADBOW is my daily driver while I wait on an ECM for our Ram truck.

'83 Silverardo XST - ZZ4 powered
'95 Jimmy SLT (Bought @131,814)
'96 GMC Jimmy LS Ret. @236651 miles


 
454cid 
Valued Contributor
Posts: 3112

Age: 46
Loc: West Michigan
Reg: 02-18-12
04-10-19 12:19 PM - Post#2763968    
    In response to gchemist

  • gchemist Said:
On my next run to HD, I'll look for a hot water ball valve.
Maybe two. Anyone remember the ID for hoses?

Needing defrost this morning, it took a long time for it to defrost a little frost. I need to check the flap cables. Something is not working right. Plus, I hear a vac leak behind the controls. Right now, BADBOW is my daily driver while I wait on an ECM for our Ram truck.



On my truck, the supply hose is 3/4" (1/2" pipe thread) and the return hose is 5/8". I have a GMT-400, but I kind of assume that was standard GM, so your Squarebody may be the same. I don't think you'll find 5/8" hose barbs in the plumbing department.

I've recently being thinking about doing this very thing again. I've got the valve, but wasn't able to mount it where I wanted and then sort of lost interested in doing it. I really don't need 200F coolant circulating into the cab, during the summer, even if I'm not pushing air through it.


99 K3500 RCLB


 
gchemist 
Senior Chevytalk Moderator
Posts: 24893
gchemist
Loc: Austin, TX 78748
Reg: 05-09-00
04-10-19 03:32 PM - Post#2763987    
    In response to 454cid

Thanks for posting sizes. I'm sure they are same size. The return is larger to prevent pressure build up. I remember seeing a four connection setup available for recreational vehicles. It connected hoses on both sides. By closing the valves, the water returned without going through the core. I have searched for pictures and have not found it again. Someone posted. Maybe a history search here might bring it up.

'83 Silverardo XST - ZZ4 powered
'95 Jimmy SLT (Bought @131,814)
'96 GMC Jimmy LS Ret. @236651 miles


 
454cid 
Valued Contributor
Posts: 3112

Age: 46
Loc: West Michigan
Reg: 02-18-12
04-12-19 05:48 AM - Post#2764093    
    In response to gchemist

  • gchemist Said:
Thanks for posting sizes. I'm sure they are same size. The return is larger to prevent pressure build up.



On my truck it's the supply hose that's larger... definitely 3/4" from the manifold, and 5/8th's to the radiator. The quick-misconnect on the intake manifold would have been pretty restrictive, Though. I just have a brass barb, now.

  • Quote:

I remember seeing a four connection setup available for recreational vehicles. It connected hoses on both sides. By closing the valves, the water returned without going through the core. I have searched for pictures and have not found it again. Someone posted. Maybe a history search here might bring it up.



Rockauto has two listed for my truck, but very few trucks (GMT-400) actually used them.

https://www.rockauto.com/en/moreinfo.php?pk=815526...

They're vacuum operated, but you can probably find a cable operated version if you dig... if you need that. GMT-400's have electric HVAC controls so the trucks/SUVs that used the valve also had a electric to vacuum conversion thing in there, too.


99 K3500 RCLB


 
gchemist 
Senior Chevytalk Moderator
Posts: 24893
gchemist
Loc: Austin, TX 78748
Reg: 05-09-00
04-12-19 06:43 AM - Post#2764096    
    In response to 454cid

Thanks 454cid.
I did find that part number. I also found another, AC Delco 15-5675. I ordered it locally. Once I receive it, I'll post a picture.
I did find the RV bypass valve. $400?? No way!

'83 Silverardo XST - ZZ4 powered
'95 Jimmy SLT (Bought @131,814)
'96 GMC Jimmy LS Ret. @236651 miles


 
VanLife 
Contributor
Posts: 149

Reg: 03-20-18
04-12-19 02:33 PM - Post#2764132    
    In response to gchemist

I believe its partially open on purpose. its part of the condensation removal system when running internal air?


when asking Questions its related to van I own: 1987 GMC 3/4 ton G2500 vandura, V6, No AC, standard length. 3speed trans(no overdrive).


 
VanLife 
Contributor
Posts: 149

Reg: 03-20-18
04-12-19 02:41 PM - Post#2764134    
    In response to 1983G20Van

I don't think its a good idea to block off the flow to the heater core using a ball valve. you could inadvertently also block the cooling for a portion of the engine block leading to over heating along the area where that coolant is flowing that goes to the heater core. The heater core in a way acts as a secondary radiator as well.

when asking Questions its related to van I own: 1987 GMC 3/4 ton G2500 vandura, V6, No AC, standard length. 3speed trans(no overdrive).


 
454cid 
Valued Contributor
Posts: 3112

Age: 46
Loc: West Michigan
Reg: 02-18-12
04-13-19 01:07 AM - Post#2764154    
    In response to VanLife

  • VanLife Said:
I don't think its a good idea to block off the flow to the heater core using a ball valve. you could inadvertently also block the cooling for a portion of the engine block leading to over heating along the area where that coolant is flowing that goes to the heater core. The heater core in a way acts as a secondary radiator as well.



We already have thermostat bypasses. I believe the heater circuit fills that function on some engines, but not ours. Our radiators should be plenty big enough to handle the cooling of the engine... just think how little cooling the heater core contributes during the hottest part of the year, when the air is bypassing the heater core.


99 K3500 RCLB


 
75gmck25 
Contributor
Posts: 386

Loc: Alexandria, VA
Reg: 12-25-07
04-14-19 06:37 AM - Post#2764199    
    In response to 454cid

Another simple check of the heater.
- Remove the glove box door
- Take off the lower panel on the heater box (couple of screws on the bottom, maybe one on the top)
- Clean out all the junk that is keeping the heater blend door from going to full cold. Also check the adjustment of the blend door cable on top of the box.

You may still get some heat out of the box, but it will be a lot better when that door seals completely.

Bruce




 
gchemist 
Senior Chevytalk Moderator
Posts: 24893
gchemist
Loc: Austin, TX 78748
Reg: 05-09-00
04-14-19 02:08 PM - Post#2764210    
    In response to 75gmck25

Ok, AC Delco 15-5675 will not work. Though it has four connections and bypass, it will not work. I don't even know how it works. It seems to be temperature controlled for bypass. I'm going to look at the FOUR SEASONS 74781 or Ranger vac bypass valve. Since the Edelbrock 1406 has full vac port available, I can use it as a vac source to bypass the heater core.

The heater can help cool an engine. However, I don't feel like roasting myself. I'm not worried about cooling. A 454 core radiator and dual LS fans keep temps at an ideal aluminum head operating temperature of 195. Fans turn on at 205 degrees and off at 190. Soon, I'll install an auxiliary fan for A/C use. Since it will be front mounted, engine over cooling should not happen.

'83 Silverardo XST - ZZ4 powered
'95 Jimmy SLT (Bought @131,814)
'96 GMC Jimmy LS Ret. @236651 miles


Edited by gchemist on 04-14-19 02:12 PM. Reason for edit: No reason given.

 
454cid 
Valued Contributor
Posts: 3112

Age: 46
Loc: West Michigan
Reg: 02-18-12
04-16-19 02:13 PM - Post#2764350    
    In response to gchemist

  • gchemist Said:
Ok, AC Delco 15-5675 will not work. Though it has four connections and bypass, it will not work. I don't even know how it works.



Yeah, I started looking that, and I was confused too. I started doing some reading on it, and I think it's may be to provide a thermostat bypass in the case of the heater core plugging.

  • Quote:
The heater can help cool an engine. However, I don't feel like roasting myself. I'm not worried about cooling.



This is something my uncle taught me many years ago. We had my grandmothers car, driving to Wisconsin, and it started running too hot, so we shut the AC off, turned on the heater, and opened the windows. It was a fullsize Buick with a 4.1L V6.

99 K3500 RCLB


 
Liberty Valance 
Contributor
Posts: 115
Liberty Valance
Loc: Euless,Texas
Reg: 07-21-14
04-16-19 02:21 PM - Post#2764351    
    In response to 454cid

  • Quote:
The heater can help cool an engine. However, I don't feel like roasting myself. I'm not worried about cooling.



This is something my uncle taught me many years ago. We had my grandmothers car, driving to Wisconsin, and it started running too hot, so we shut the AC off, turned on the heater, and opened the windows. It was a fullsize Buick with a 4.1L V6.



Many years ago we were always told when overheating, turn on heater. This was before dual electric fan setup. Now I think the solution is to turn on AC so both fans are working.

1974 Cheyenne 10 LWB 350/TH350/AC/4 BBL Quadrajet


 
454cid 
Valued Contributor
Posts: 3112

Age: 46
Loc: West Michigan
Reg: 02-18-12
04-18-19 04:47 AM - Post#2764448    
    In response to Liberty Valance

  • Liberty Valance Said:

Many years ago we were always told when overheating, turn on heater. This was before dual electric fan setup. Now I think the solution is to turn on AC so both fans are working.



Running the AC is going to make the engine work harder, generating more heat, plus the heat removed from the interior of the vehicle has to be dissipated. I would hope manufacturers would have sense enough to have the PCM turn on both fans when an engine is running hot.


99 K3500 RCLB


 
gchemist 
Senior Chevytalk Moderator
Posts: 24893
gchemist
Loc: Austin, TX 78748
Reg: 05-09-00
04-21-19 06:24 AM - Post#2764712    
    In response to 454cid

Ordered the Four Seasons 74781 valve. It's vacuum operated. A mounting bracket or hole will added to the right wheel well cover. I can bypass the vac operation by using a zip tie. Using a vac operation set up, allows the valve to open up and help engine cool down after turning it off. I'll do a mock up and post pictures.

Once I order a TPI TV cable to replaced the frayed cable, BADBOW will go a friend's house for work.

Ya'll can follow the 700R4 frayed TV cable post here: https://www.chevytalk.org/fusionbb/showtopic.php?t...

Parts on the list for installation: heater by pass valve, new TV cable, A/C front condenser electric fan, reinstall grill bow tie emblem, fit right header collector leak, new window tint, and check the A/C-heater core box for operation.

'83 Silverardo XST - ZZ4 powered
'95 Jimmy SLT (Bought @131,814)
'96 GMC Jimmy LS Ret. @236651 miles


 
Mad Professor 
Poster
Posts: 99

Reg: 12-30-08
04-21-19 06:24 PM - Post#2764776    
    In response to gchemist

I used a ball valve on mine, but it is a 292 w/4 core radiator.

If you still want a flow a 3-port ball valve on the inlet, and a simple t-fitting/conector on the outlet, might be the ticket.

3-way ball valves

They make electrically actuated ones but I'm not sure if 12V? That is you could wire a switch to the dash.

62 Willys wagon
67 CJ5 Buick V6 w/OD
68 Camaro RS/SS , 69 LT1 350, M22
73 C10 292 6, M21 muncie/hurst, 3:73 posi
89 S10 baja package







 
454cid 
Valued Contributor
Posts: 3112

Age: 46
Loc: West Michigan
Reg: 02-18-12
04-21-19 10:46 PM - Post#2764791    
    In response to gchemist

  • gchemist Said:
Using a vac operation set up, allows the valve to open up and help engine cool down after turning it off. I'll do a mock up and post pictures.



But you won't have circulation, when it's off... unless you're using an electric pump on a timer?

  • Quote:
reinstall grill bow tie emblem



I need to do that too... actually just install the used grille that I have, that already has the emblem.


99 K3500 RCLB


 
gchemist 
Senior Chevytalk Moderator
Posts: 24893
gchemist
Loc: Austin, TX 78748
Reg: 05-09-00
04-22-19 04:46 AM - Post#2764799    
    In response to 454cid

When the truck is off, the vac loss will open the bypass valve. Water in the heater core will be cooler than engine/radiator water. The core water will pull heat out of the cooling system. I don't want standing still inside the core either.

Since I have remove the grill to install the auxiliary cooling fan, it's a great time to install the emblem. I have not found a replacement emblem with studs for an 88-91 grill. I had it glued on. I'm lucky it lasted a few years without falling. This time, I may use vinyl to cover the bow tie. Vinyl is easy to replace every few years.

'83 Silverardo XST - ZZ4 powered
'95 Jimmy SLT (Bought @131,814)
'96 GMC Jimmy LS Ret. @236651 miles


 
454cid 
Valued Contributor
Posts: 3112

Age: 46
Loc: West Michigan
Reg: 02-18-12
05-04-19 05:38 AM - Post#2765691    
    In response to gchemist

Did this ever get finished?

99 K3500 RCLB


 
gchemist 
Senior Chevytalk Moderator
Posts: 24893
gchemist
Loc: Austin, TX 78748
Reg: 05-09-00
05-05-19 04:43 AM - Post#2765749    
    In response to 454cid

Not yet. I have the valve ready for installation. I'm still looking for a TV cable solution. My setup is unique. With help from the Performance Section, I think we have a solution. A TPI TV cable should be close enough to correct length for use. I'll post valve and install pictures.

'83 Silverardo XST - ZZ4 powered
'95 Jimmy SLT (Bought @131,814)
'96 GMC Jimmy LS Ret. @236651 miles


 
gchemist 
Senior Chevytalk Moderator
Posts: 24893
gchemist
Loc: Austin, TX 78748
Reg: 05-09-00
07-04-19 06:11 PM - Post#2769952    
    In response to gchemist

Liberty Valance has provided a nice picture of a mounted auxiliary fan. I'm adding one to help with a/c cooling. If it's not enough, the trinary switch will also activate the dual LS cooling fans. I'll have to test the system. Hopefully the auxiliary fan is enough. Mine will have to mount on the driver side. The passenger side has a large external transmission oil cooler. I'll post pictures when I do the project. It will be at least 2-4 weeks out.

Attachment: fan.jpg (299.5 KB) 5 View(s)


Photo credit: Liberty Valance.


'83 Silverardo XST - ZZ4 powered
'95 Jimmy SLT (Bought @131,814)
'96 GMC Jimmy LS Ret. @236651 miles


 
gchemist 
Senior Chevytalk Moderator
Posts: 24893
gchemist
Loc: Austin, TX 78748
Reg: 05-09-00
07-18-19 06:44 PM - Post#2771019    
    In response to gchemist

Here is a pic of a heater core bypass valve. It's a Ranger part number. Completely closed, a little water may still flow through. For now, I plan to tie the valve up for bypass. Later, I'll experiment with vacuum control. The carb has a full vacuum port that I can use. No danger in water getting into the vacuum part. If this valve does not work out after testing, I'll probably switch to ball valves.

Attachment: bypassvalve.jpg (45.21 KB) 4 View(s)


Heater core bypass valve.


'83 Silverardo XST - ZZ4 powered
'95 Jimmy SLT (Bought @131,814)
'96 GMC Jimmy LS Ret. @236651 miles


 
bronco777 
Poster
Posts: 6
bronco777
Loc: Central Valley, CA
Reg: 04-05-15
08-20-19 10:20 AM - Post#2773675    
    In response to gchemist

The simplest way to bypass the heater core is to connect the inlet and outlet hoses using a heater hose connector. Dorman makes one that is 3/4” x 5/8” and is part #47080. I do this in the summer on my ‘89 Suburban so the A/C doesn’t have to cool any warm air coming off the core. In the winter I reconnect the hoses to the heater core for heat. Cap the heater core tubes with correct size rubber caps (Dorman makes rubber vacuum caps that work), or just use painter’s tape. This is also a short-term solution to a leaking heater core that is dripping coolant into the truck cab.

1989 Suburban 3/4 ton, 4x4, 5.7L TBI stock
1972 Ford Bronco


 
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