Installing valve in water line from head to heater core

[Blakers]

I know this question was discussed years ago -- it might have even been back when I had my 95 12-valve.

Some have suggested installing a valve in the heater hose between the head and the heater core to prevent hot water from circulating through the heater core in the summertime. Lots of older vehicles I have had controlled their heat this way, and most just closed the valve and deadheaded the water flow. I think I even have a good boden cable heater valve somewhere laying around.

Who's done this and have you had any negative results? I know the 5.9 engines are used in many applications where they don't even pull heat off the engine and that hole in the head is just plugged. Thanks.

 

[Ozymandias]

Never done, never needed. It also takes away coolant flow from cylinder 5&6.
The engines you mention have usually a much lower power rating. So I don't take the chances on something that is for nothing.

 

[Darkbloodmon]

Ideally I wouldn't see a problem if you have a modified coolant routing for the heater hoses but on a stock setup just putting a valve in would stagnate the coolant circulation around cylinders 5&6 like @Ozymandias said.

.02, if its meant to have coolant running through it I wouldn't block it, what are the chances the hoses coming from the heater core shrink at the connections from the loss of thermal expansion and then start leaking when you flip the valve on. This is assuming you still have the factory hoses.

 

[Blakers]

I wouldn’t think the design of the engine cooling system would rely on the small amount of circulation going through a 5/8” hose.

 

[Crunch]

My concern would be standing water in the heater core. It can't be good just sitting there and not circulating. And then when you open the valve in the winter, all the sludge and corrosion in the heater core gets pushed into the cooling system.

 

[Darkbloodmon]

I wouldn’t think the design of the engine cooling system would rely on the small amount of circulation going through a 5/8” hose.

I installed a home made coolant filter kit routing the outlet of the heater core and rear head port from 5/6, both pushing into the filter and then the outlet of the filter being pulled directly into the water pump inlet. I don't have an estimate to the volume that passes in a time frame but even with it being a bypass filter I could bottle my coolant out the pet cock and put it on a parts store shelf its that clean.

This to say that it may not be much by looking at the hose size but the heat and pressure pushing coolant from one of the hottest areas of the head; does move quite abit of coolant at operating temp. Even more so when the truck is loaded or towing.

 

[bigceltic]

Some have suggested installing a valve in the heater hose between the head and the heater core to prevent hot water from circulating through the heater core in the summertime. Lots of older vehicles I have had controlled their heat this way, and most just closed the valve and deadheaded the water flow. I think I even have a good boden cable heater valve somewhere laying around.

Just as a point of reference, I have towed my 9000lb trailer up and down the CO mountains, to Grand Canyon via NM and AZ, and out through Utah and back a few times (most recently last summer - July, towing in 100 degs - to Zion and back) and have never had any overheating problems. My experience is that the cooling system is more than adequate and you don't have to worry. AC nice and cool with no issues.

 

[Blakers]

Just as a point of reference, I have towed my 9000lb trailer up and down the CO mountains, to Grand Canyon via NM and AZ, and out through Utah and back a few times (most recently last summer - July, towing in 100 degs - to Zion and back) and have never had any overheating problems. My experience is that the cooling system is more than adequate and you don't have to worry. AC nice and cool with no issues.

Do you have your heater hose valved off (deadheaded), or does it bypass the heater core and flow back to the front of the engine?

 

[Blakers]

My concern would be standing water in the heater core. It can't be good just sitting there and not circulating. And then when you open the valve in the winter, all the sludge and corrosion in the heater core gets pushed into the cooling system.

It's all treated with the same high quality antifreeze. I don't see it sitting there a few months is going to matter. All the older vehicles used valves in the heater hoses to control the heater temperature, so it's not a new idea by any means.

 

[bigceltic]

Do you have your heater hose valved off (deadheaded), or does it bypass the heater core and flow back to the front of the engine?

I have nothing special - all stock.

 

[User113]

You can buy commercially available "heater core bypass valves" to do this.

Three points to consider:

• These valves keep fluid flowing out of the head and back to block for those who worry about maintaining flow through the loop for cylinders 5 & 6.
• I understand also that they have a tiny bleed passage that very slowly circulates the fluid through the heater core so that it doesn't "deadhead" and stagnate in the heater core.
• Finally, it keeps all that unnecessary heat out of your HVAC box when all you want is really cold air.

Win-win and bonus.

 

[AH64ID]

There isn’t a need for this, and as mentioned reduces flow to cylinder 5&6.

5&6 already run hotter than the others, and you have a greater risk of blowing out the rear freeze plug from too much pressure.

Keep the plumbing intact and if you’re having issues fix them, don’t bandaid them.

Aside from the added flow of a coolant filter my stock cooling system was more than adequate for the 415rwhp my 05 made, even towing hard on 100° plus days.

 

[BigPapa]

The next project on my ‘98, had I kept it, would’ve been putting in a valve similar to this. My plan was to use 45* barbs and work it into the metal tubes running the length of the head.

 

[Blakers]

You can buy commercially available "heater core bypass valves" to do this.

Three points to consider:

• These valves keep fluid flowing out of the head and back to block for those who worry about maintaining flow through the loop for cylinders 5 & 6.
• I understand also that they have a tiny bleed passage that very slowly circulates the fluid through the heater core so that it doesn't "deadhead" and stagnate in the heater core.
• Finally, it keeps all that unnecessary heat out of your HVAC box when all you want is really cold air.

Win-win and bonus.

Sound good! Any idea who has these valves? I’m sure you can get 3-way valves from supplyhouse.com, but not specifically for trucks.

 

[User113]

The red text in my message is a hyperlink and will take you to at least one source (S & P Automotive). BTW, it's functionally equivalent to the brass one posted above by BigPapa, which is available on Amazon. Alternatively, just search for "heater core bypass valve" in your favorite non-Google search engine and you'll see many others.

The one I linked to comes with a cable control, like the old "choke" on entry model cars back in and before the '60's before automatic chokes became standard. Convenient if you run it inside the cab.

The one BigPapa highlighted is clearly manually controlled via the red handle. Not quite as convenient as remote control via a cable.

If you search as I suggested above you will also find replacement heater core bypass valves for European vehicles like Mercedes, Jaguar, BMW, etc. that are electrically controlled, but they all do the same thing, and could easily be adapted in our trucks. Electric control would probably be the most convenient of all. If you do go with the European valves, it would be easier if you looked for the valves with 4 ports rather than 5, but the 5 port valves will work too. It's just that they're designed to flow to a split heater core (passenger side/driver side or something like that). You would also be paying for a redundant valve and motor.

 

[Ozymandias]

Again, what for? Adding another point of failure?
As long as the AC is in order there is absolutely no benefit from that valve.

 

[BigPapa]

As long as the AC is in order there is absolutely no benefit from that valve.

How so? I bypassed my heater core for a couple weeks a few years ago during the summer. My A/C was notably cooler.

 

[Blakers]

Again, what for? Adding another point of failure?
As long as the AC is in order there is absolutely no benefit from that valve.

Is the heater core before or after the air conditioner evaporator?

 

[Blakers]

It would be really interesting if someone who has this bypass water system were to take some accurate measurements of the temperature coming out their vents with the water going fully through the heater core and with the water bypassed. Do this with the temperature control set to coldest with just airflow and with ac airflow. Switch back and forth allowing time for the temperature to stabilize in each case. I would do it in the shade so the heat from the sun is not an issue. And have the engine up to normal operating temperature.
This should give us some accurate comparisons of just how much cooler (or not) the air is with the water bypassed.

 

[Signal73]

My 2019 gained 10 degrees cooler air. The 4.5 gens have some pretty pathetic AC vent temps. 53 degrees without the valve.