Heater core shutoff valve…revisited

[Tucson38]

Some time ago another poster suggested putting a shutoff valve in the heater hose to minimize the heat going into the cab. I picked up a $10 universal shutoff and installed it. Makes a very noticeable difference in the cab heat level. My A/C seems to be much more effective now so a big thanks to the original poster. Pretty important given my geographic location.

[tucsonjwt]

I used a plumbing style PEX 3/4" ball valve. The automotive style I got from O'Reilly leaked - very cheap product. It does help to stop hot coolant from entering the heater core and adding heat to the cab. I have heard that this is a common mod on commercial trucks in "Tucsonistan."

[Tucson38]

Now why didn't I think of that? Great idea.

[TexasJeff]

I have bought my pex valve but not yet installed it, so glad to hear that it works so well.

[willem445]

Does anyone have a link to the hose they are using? Someone before me thought it was a good idea to bypass the heater core altogether so I have a mangled heater core hose at the moment which is very leaky.

[tucsonjwt]

I like good quality heater hose from NAPA. The other auto parts stores have cheap quality which does not hold up very well.

As a side issue, you can install a "bypass" hose with two nipples in the ends of the heater hose instead of a shutoff valve. You would have to disassemble the connections and store the bypass hose during the winter, and probably lose a little coolant in the process. This would keep the coolant circulating completely in the cooling system while bypassing the heater core in the summer. I have a bypass hose installed on my Cavalier because the heater core is leaking and I don't have the nerve or skill to disassemble the entire instrument panel and supporting structure to replace the core (a pro would charge about $1000 for the job.)

Gates sells bypass hoses of various sizes. I got mine from NAPA.

Amazon.com: Gates 18701 Molded Heater Hose:...

[68Timber]

I'm going to put one of those on my 85 this weekend, great idea. I had an old Scout once and IIRC it came with one from the factory.

[LuckyLightning]

I think I need this, my cab gets inexplicably hotter after driving for a bit. I went ahead and got the valve and the hose clamps, but which hose do I put the valve in: the one coming from the water pump, or the other hose?

[tucsonjwt]

I put mine on the 5/8" line. My truck is not available now so I cant' look at it to tell you the source of that line. If you are concerned about proper routing, installing a bypass loop would be better.

[LuckyLightning]

Thanks tucsonjwt, but I want to be able to turn it on and off as needed.

[wilkin250r]

I know the one connected to the intake manifold is the "feed" line, and after looking at a few pictures in another thread, I'm 90% certain this is the 5/8 line.

The return line either connects to the water pump, or to the radiator, and I'm 90% certain this is the 3/4 line.

But I don't think it really matters which line you connect to. Flow is flow. Blocking the return is just as effective as blocking the feed, you're not going to "build up" or "overflow". If it was a high-pressure pump you might see a difference, but the pressure created by the water pump in a vehicle cooling system is almost insignificant when compared to the pressure created by HEAT, and that pressure will exist throughout the entire system, so you're not going to create a pressure overload.

Put the valve in either line, it doesn't matter.

[LuckyLightning]

Thanks wilkin250r, I also found this thread which aligns to what you said.

Quick question though: does the water need to flow? I mean, am I going to cause any damage or anything if I have this valve shut off for the rest of the summer?

[wilkin250r]

I've seen plenty of old cars and trucks (including my own) with the heater completely removed and the outlets blocked off. So I don't think you'll damage the water pump, or thermostat, or any other component in the system by not flowing.

Now, there IS a slight chance that the water sitting stagnant in the heater core could cause problems. It might cause corrosion, or bacteria growth, or some other issue caused by lack of circulation. But that has a lot of factors, like amount and quality of antifreeze, any corrosion already present, amount of impurities in the water you used, ect ect. Too many factors to give you a definitive answer, but the SOLUTION would be to open that valve every couple of weeks and let the coolant circulate a little.

[LuckyLightning]

Thanks wilkin250r, that's a good idea to let it circulate every few weeks.

[Chevy_mud_truck]

I know on some of the cars if built that had the heater core removed we would drill a half dozen small hole it the outer edge of the thermostat to let a little coolant flow till the thermostat opens I've seen them boil over a little if you start driving to hard before thermostat opens

[LuckyLightning]

Yeah, I did notice the truck runs a little warmer now that I've installed the valve and have it shut off. Will update if I (need to) change anything else.

[Liberty]

On my truck there hasn't been any noticeable difference in operating temperature with the valve closed, if anything the engine runs cooler and its been pushing near 100 here in North Texas.

[Bigstevex4]

I posted a picture of shut with cable not best picture. I had too use heat last week one night. We have to much temp variance. 45 in morning 85 by noon.

[Tucson38]

Originally Posted by Liberty

On my truck there hasn't been any noticeable difference in operating temperature with the valve closed, if anything the engine runs cooler and its been pushing near 100 here in North Texas.

Ditto here in Tucson.

[80Sierra3500]

I put one of these on my truck a LONG time ago. I too was concerned about modifying the coolant flow until I realized there's already a thermostat bypass hose between the manifold (just underneath the thermostat) and the water pump. I've never noticed any difference in operating temperature.

As someone already mentioned, you can drill a small hole in the thermostat to make sure a small amount of coolant is flowing through it so you know the thermostat is actually feeling the coolant temperature.

[wilkin250r]

Isn't that a vacuum-operated shut off valve? I wonder if there is a way to make THAT work on demand.

[nonstop]

Originally Posted by wilkin250r

Isn't that a vacuum-operated shut off valve? I wonder if there is a way to make THAT work on demand.

Sure is - vacuum operated valve with a vacuum solenoid to a toggle switch. Have wanted to do it, just trying to get time!

[KQQL IT]

Maybe not an Arizona issue but the A/C freeze's up when I turn off the heater hoses in the peterbilt.

[LuckyLightning]

I just drove the truck today for a few hours in the hottest part of the day. I think what I saw was the temp rising before the thermostat opened up. I saw it happen again today - the temp would rise until the thermostat opened up, then go back down to normal. Interesting thing was it happened every time I turned off the truck for more than a few minutes (such as when pumping gas). I assume this is normal operation, but I never noticed it before.

[racerop]

Originally Posted by LuckyLightning

I just drove the truck today for a few hours in the hottest part of the day. I think what I saw was the temp rising before the thermostat opened up. I saw it happen again today - the temp would rise until the thermostat opened up, then go back down to normal. Interesting thing was it happened every time I turned off the truck for more than a few minutes (such as when pumping gas). I assume this is normal operation, but I never noticed it before.

I had a car have the same symptoms as what you are describing. I would flush/refill with new coolant and replace the thermostat. The thermostat is probably sticking while opening.