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Bypassing the heater core in the summer

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Old Mar 1, 2025 | 11:27 AM
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Default Bypassing the heater core in the summer

1978 Caprice. LM7 5.3, 4l60e. All stock, daily driver swap. (sorry, some of earlier pictures have stopped working)
https://ls1tech.com/forums/conversio...5-3-4l60e.html

I looked into a lot of options for blocking off my heater core during the summer. I wanted to keep things as reliable and simple as possible as this is my daily driver that I've had for 27 years. I decided to go with this option, and will choose to manually turn the valve at the beginning of each season. Also, I've purchased a heater core restrictor, which on older cars like mine prevents the water pump from over pressurizing the heater core and causing failure (I found this out the hard way when I didn't include one and my heater core was damaged). I'm thinking that if I use the partially opened valve as a restrictor, then I may not need to add the stand alone restrictor, causing one less set of clamps and an extra piece under the hood (the factory GM restrictors are plastic and are known to fail with age).




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Old Mar 2, 2025 | 07:18 AM
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This seens fairly simple and you only loose 1 cup of coolant .


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Old Mar 2, 2025 | 08:19 AM
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This is my $3 solution to that, been in the car since 2010 no problems.


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Old Mar 9, 2025 | 07:33 PM
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Originally Posted by the_merv
This is my $3 solution to that, been in the car since 2010 no problems.
I have done something similar with no problems.
Why do some people say the water pump outlet/inlet need a bypass hose if the heater is not connected? Real reason? Myth? BS?
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Old Mar 10, 2025 | 08:09 AM
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Did this on my last ls swapped Sonoma
https://www.s10forum.com/threads/how...ac-mod.412746/
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Old Mar 10, 2025 | 07:37 PM
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Originally Posted by mrvedit
I have done something similar with no problems.
Why do some people say the water pump outlet/inlet need a bypass hose if the heater is not connected? Real reason? Myth? BS?
I know there's a big hole between the two, take the Thermostat Housing off you see it. I've never measured to see if that's blocked by the T-stat but then again never had a reason to investigate that.

My car runs the same Valve closed or open.
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Old Mar 11, 2025 | 10:00 AM
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I run this block-off made by Jaywire. Blocks off the bypass. The bypass (you can feel the passage easily with your fingers) routes hot coolant back in the engine.


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Old Mar 12, 2025 | 08:24 AM
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Originally Posted by Vetteman61
, I've purchased a heater core restrictor, which on older cars like mine prevents the water pump from over pressurizing
A restrictor or shut off valve on the inlet will not change the pressure in a heater core.
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Originally Posted by Pro Stock John




I run this block-off made by Jaywire. Blocks off the bypass. The bypass (you can feel the passage easily with your fingers) routes hot coolant back in the engine.
#racecar
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Old Mar 14, 2025 | 04:13 PM
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From: Little Austin
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You can install a simple block off valve, provided you use something like this:

https://www.lojkits.com/products/ls-...4pdh5bIdiwNjZU

Andrew
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