Heater core bypass

[upon1]

Im installing a vintage air heater in my '55 and it has a servo motor to shut off flow to the heater core, should I plumb a bypass into the heater hoses before it gets to the heater shut off?

[mongocanfly]

when I did my swap they told me to not block off the heater hoses...they said if I wasn't going to run a heater to put a loop on the engine side heater hose outlets...they said with the thermostat where it is it needs to see flow.....again .. and this is what I was told..
there was another member here that had overheating issues and he had his fittings capped off....he installed a loop and problem solved...
so...I would say it needs to bypass....

[DLW]

I heard the same thing. Some say it ran hotter with a regular non-bypass heater valve and some say no difference.

Seems if you want to use the bypass valve, you have to use a separate potentiometer like this one https://www.oldairproducts.com/produ...ve-kit-50-1555 to control heat.

Or you have to get clever with some wiring to make it work with the VA controls.
There is a version that works with vacuum, but don't want to bother with that one myself.

[DLW]

Just found this http://www.ffcars.com/forums/42-fact...tructions.html

Pretty cool way to mod the wiring to work with the VA system using the 50-1555 kit.

[upon1]

I was thinking of just putting a “t” in the pressure hose and one in the return hose before the heater shut of valve and connecting them together. With the valve closed the coolant can loop back. Valve open, it’ll take the path of least resistance. Like to keep it simple.

[ls1nova71]

I hear about this all the time, but in my 17 years of driving LS swapped cars with at least 250k miles combined, I have never had a problem running a block off heater valve. Maybe I'm just lucky? I did put a return type vacuum controlled valve off of an Astro van, on my truck and never noticed any difference at all....

[upon1]

So essentially it’s not blocked off if it has a return valve. Coolant can still circulate through the heater hoses off of the pump. Correct?

[ls1nova71]

Originally Posted by upon1

So essentially it’s not blocked off if it has a return valve. Coolant can still circulate through the heater hoses off of the pump. Correct?

No it wouldn't be blocked if it has a way to the pump. Doing it the way you suggested by putting two "T"s would work and although some coolant will always flow through it, it wouldn't be enough to ever notice in decreased heating I wouldn't think. This is what I used, it's from a 2001 Astro van. But like I said before, I haven't noticed a difference between the truck with that valve and my other cars with the Vintage Air valve that shuts it off completely.

[DLW]

I have the VA one way valve in mine now, seems to work ok and I run around 205* but I did not do any comparison to a crossover, and I have not made it out of my driveway yet. My factory equipped LS engine came with a crossover so apparently GM thought it was necessary. There is a couple folks that did extensive testing to show it does make a difference if your actually testing and measuring temps.

I think unless your at max AC or completely turned off in the VA setup, the HCV will always be open somewhat anyway and be much less noticeable of seeing any changes in temp.

I have ordered a bypass already and have my system drained anyway doing a cam swap, so I will just change it.

I also found this part interesting https://www.lojkits.com/products/ls-...r-bypass-block. When your one way valve is closed it just redirects through the H-channel. Should work similar to the double "T" mentioned before.