Heater Core Bypass - Page 2 - JeepForum.com
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post #16 of 37 Old 07-20-2021, 05:36 PM
Heg87T
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My older GM cars have a heater control valve in one of the heater core hoses. Vacuum line closes it when you move the temperature selector in the cabin to cold.


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post #17 of 37 Old 07-20-2021, 05:39 PM
dln1962
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I've installed quarter-turn valves similar to what @cDee63 posted on many vehicles over the years. Never saw a decrease in engine cooling but it sure helped keep the folks inside a bit cooler. Many farm tractors with factory cabs used to come with shut-off valves on the heater taps from the factory; the manuals said to shut one of them off in warm weather for more effective A/C operation. You don't want to shut both off because on a really hot day expansion can cause the coolant trapped in the core to actually rupture it.
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post #18 of 37 Old 07-29-2021, 07:05 AM
Liduno
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Adding a shut off valve to one of the hoses sounds easier than doing the blend door mod. Thanks for the idea guys. Iím going to test it with a pair of vise grips on one hose today. I know there wonít be any actual coolant flow, but I wonder if the heater core will get hot eventually just from the rest of the coolant heating up. Someone mentioned not blocking off both hoses, because it could build pressure in the heater core.

My original plan was to just bypass the heater core but I like the idea of being able to use my defroster when needed.
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post #19 of 37 Old 07-29-2021, 10:19 AM Thread Starter
jhawkins002
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So a part of the discussion I have not seen mentioned yet here but I have seen discussed on other vehicle forums is this: if you block flow (as opposed to looping) you are preventing the cycle of coolant from running as engineered through that part of the system. Under normal operating conditions this probably isn't a huge problem but if the engine is under heavy load in less than ideal conditions then a degree or two here and there makes a big difference. This is why factory engineered solutions for this type of setup typically features a diverter setup to omit the heater core but otherwise allow the coolant to continue on through the system - as opposed to a simple on/off valve. Like this, for example: https://www.amazon.com/Cable-Operate...7575229&sr=8-4.
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post #20 of 37 Old 07-29-2021, 04:04 PM
cDee63
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The only part being blocked from coolant flow is the heater core in our application. Like mentioned running coolant through the heater core was only practiced in the old days on basic trucks and equipment. Most had a valve either run with a cable in the real old days or vacuum which was and still is very common. The main reason the manufacturers went back to full flow was a cost/reliability issue. The temp control is now again done with diverting and blocking doors vs actually cutting the coolant flow off from the heater core. No valve is one less thing they have to source or make saving a couple bucks and it is one more thing not to fail. The amount of heat dissipated through the heater core enclosed in a box with no air flowing through it would be negligible and would have no effect on the cooling system performance. I originally did loop mine with a preformed hose that did a 180, looped it right off the thermostat housing the heater hoses come off and return to. I had to add a valve and put the core back in the loop only because when it gets real humid and hot, during a thunderstorm for example, the windows will fog forcing the need for some warm defrost air. Does not happen very often but when it does I have the ability to open the core back up for business and close it back down again at will. That valve posted is what the old cars used with a cable vs vacuum actuation. My old XJ had a factory one that looked just like it with a vacuum pot instead.

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post #21 of 37 Old 07-29-2021, 06:02 PM
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Quote:
Originally Posted by Liduno View Post
Adding a shut off valve to one of the hoses sounds easier than doing the blend door mod. Thanks for the idea guys. Iím going to test it with a pair of vise grips on one hose today. I know there wonít be any actual coolant flow, but I wonder if the heater core will get hot eventually just from the rest of the coolant heating up. Someone mentioned not blocking off both hoses, because it could build pressure in the heater core.

My original plan was to just bypass the heater core but I like the idea of being able to use my defroster when needed.

without the ability to flow, the heater isn't going to heat up. mopars used to be built with a valve in the water circuit, to shut-off hot water from entering the cab. you only need one valve, and the advice is sound. those valves cost money, as did the cable/vacuum system to operate it. saving money is how any manufacturer looks at what goes into a car. those pennies add up, when you look at all of the parts involved in building a car.



your house has a hot water heater. go to the tank, and follow the hot water line, from the tank towards your faucets. see how quickly the heat vanishes from the pipe, as you move away from the heater. with no flow, the heat in the tank has nowhere to go. think of how long it takes to get hot water in the shower, when you first turn on the hot water (no comments from you tankless guys) . once you shut it off, the hot water in the pipe cools, over time. an hour later, the water is cold again.

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post #22 of 37 Old 07-30-2021, 12:32 PM
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i dont suppose there's a full write-up somewhere? i know its just 1 valve in 1 hose but still....

is this the right part?



https://www.amazon.com/gp/product/B0...KIKX0DER&psc=1
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post #23 of 37 Old 07-30-2021, 04:35 PM
cDee63
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If that is a 3/4 ID barb it is exactly the right part. When cold of course cut one hose, I did the "upper" one for room to swing the handle on or off. A small amount of coolant will leak so have a towel or rag handy under it. Slide one end of the hose on the valve and a hose clamp of your choice, the other hose end on the other end of the valve, clamp it and you're almost done. Let the engine heat cycle once with the valve open and cool completely with the valve still open. Bleed the system in the normal way and then close the valve. This is how mine looks.
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20210717_084916.jpg  

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post #24 of 37 Old 07-31-2021, 03:36 AM
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Quote:
Originally Posted by anarky321 View Post
i dont suppose there's a full write-up somewhere? i know its just 1 valve in 1 hose but still....

is this the right part?



https://www.amazon.com/gp/product/B0...KIKX0DER&psc=1
As, when, and if I get round to it, I'll clamp the heater hose with a simple brake hose clamp.
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post #25 of 37 Old 07-31-2021, 12:49 PM
Liduno
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Just ordered that valve. I drove around for the last couple days with the vice grips on the heater hose, AC is about 20į cooler coming out of the vent.

I contemplated getting that Ford heater control valve, but I didnít like the fact that it was plastic.
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post #26 of 37 Old 07-31-2021, 06:49 PM
anarky321
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im doing this tomorrow - i just finished replacing the evaporator and heater core so perfect time to do it

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post #27 of 37 Old 08-01-2021, 01:00 AM
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Originally Posted by Liduno View Post
Adding a shut off valve to one of the hoses sounds easier than doing the blend door mod. Thanks for the idea guys. Iím going to test it with a pair of vise grips on one hose today. Not a good idea I know there wonít be any actual coolant flow, but I wonder if the heater core will get hot eventually just from the rest of the coolant heating up. Someone mentioned not blocking off both hoses, because it could build pressure in the heater core.

My original plan was to just bypass the heater core but I like the idea of being able to use my defroster when needed.
There's no real need to clamp both hoses.
You will get nearly all the benefit by clamping the feed hose as close to your engine as possible.

I'm not sure what you mean by a vice grip.
What I know as a vice grip will damage a hose if it is too tight.

This is the sort of thing I use.
Clamped tightly enough to just close the pipe.
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post #28 of 37 Old 08-01-2021, 10:47 AM
anarky321
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err did i put it on the right hose? i put it on the one that goes down to the crankshaft..(im still learning what goes there...is the top part the thermostat and bottom is water pump? )

edit: is it better to cap the one coming from thermosatat or water pump? i did the water pump one it seems...which side is the feeder side?

edit2: going to rephrase the question - the flow of coolant is waterpump>heatercore>tstat in that direction right?


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post #29 of 37 Old 08-01-2021, 04:33 PM
anarky321
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ok so I just did the valve on the one with the leaking heater core - my question is do I need to cap the 2nd hose too to prevent any fluid from going into the heater core or is that 2nd hose going to naturally just drain and stay at 0 psi once the heater core leaks out?

I tapped the water pump hose again, like the 1st jeep - the hose that concerns me is the heatercore>tstat hose (the one on top)

edit: i was thinking some more about this...if i have a leaky heater core and I closed off the water pump side....won't that lead to it trying to suck in air through the hole in the heater core on the Tstat side?




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post #30 of 37 Old 08-01-2021, 07:59 PM
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Quote:
Originally Posted by anarky321 View Post
i dont suppose there's a full write-up somewhere? i know its just 1 valve in 1 hose but still....

is this the right part?



https://www.amazon.com/gp/product/B0...KIKX0DER&psc=1
That's actually not the best valve to purchase as it has a drain on the side. It's usable if you put some Vibra-Tite on the round screw, but why take the chance for something that is unnecessary? I made the same mistake myself. Here`s a link to the valve minus the drain for anyone who wants one. I just purchased the red and blue handled two pack, and installed one in each of my jeeps. Haven't had a sweltering, 90 degree day yet, but seems icy cold in the cabin for mid-70's days so far.

https://www.amazon.com/Full-Port-Val.../dp/B00MA9DQ50
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