When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
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).
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?
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.
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.
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.
Bypassing the heater core in the summer 
