kodpkd

1968 327 no AC. Summer is here, it gets hot. It has a new heater core. With summer here I don't need the extra heat. I wanted to make sure at least no heat is coming from the core. I installed a shutoff valve on the hose from the engine to the lower heater core connection. Can anyone tell me if this might cause any issues? I just got back from a test drive in 90* weather. Everything seems ok, no bursting hoses.

7T1vette

Should cause you no problems....other than remembering to turn on or shut off when the season changes.

kodpkd

I have done lots of searches and can't find how the heat is shut off with the "Hot/Cold" wheel on the center console. Is it just a vent to shut off the heat or does it actually shut off water flow to the core?

Edit: It has to be just a vent shutoff. I installed the core and there are not any coolant valves into or out of the core.
The new shutoff should make it cooler inside.

Buccaneer

The only issue with that is if you ever have a cooling issue (summer) and if the motor starts to get hot, you will not have the ability to use the heater core to help cool down the motor by selecting heater and save a "possible" overheat condition. I guess you could always stop and turn it ON if needed, but that would also be assuming that you could pull over and do that quickly enough. Lots of room for error IMO. It would leave it along and just turn OFF the heat on control panel. Am I missing something?

Richard454

No problem at all-

Depending on how long your drives are- only closing one hose off- eventually the water in the heater core will get up to operating temp (180 degrees) thanks to convection.

The several times I did the Hot Rod Power Tour in my 73 ( 3K miles in a week in June w/o AC)-

I closed both lines off- and it made a big difference.. Don't believe me - just ask my wife!!!!

Tiger Joe

Nothing wrong with that. Been doing it for years.

Vette5311

Interesting post. I had not thought about adding 2 of them.

kodpkd

Great.... I don't have cooling issues, even when idling. Indicates about 170* when it's hot out.

Bikespace

Later year cars have an actual valve that is closed with vacuum (normally open with no vacuum applied). You can imagine how well these 40 year old valves work, but repros are available.

The only problems I see with your solution is that the input to the heater core is still pressurized, so any leak will still allow coolant to ruin your carpet. Also, some say that some bypass flow is required in certain engines, so rather than use valves, I have a short loop of hose, with a restrictor, that bypasses the heater core. Of course, to get heat again, I have to disconnect and reconnect coolant hoses, which is messy.

Mooser

Once in a while turn it back on just to sort of "flush the core"
Been using one for years, no issues
M

Torqued Off

I just installed the factory vacuum shutoff, and it works perfectly. No excessive heat in the car.

Rescue Rogers

remember on a 68 the expansion tank is in line with the heater and the coolant is forced one way though the tank. If you block one side and it gets hot out....you may end up with issues. Ive been looking at the same issue and i am going to add 2 shutoffs and a crossover with a shutoff. SO I can open the bypass and shutoff the heater. IF you shutoff the forced water side you might be okay but hot water is still going to get to the radiator and it has to get to the expansion tank

Richard454

Blocking off both hoses doesn't effect the system EXCEPT no defroster....

Closing one hose will stop the flow of both hoses- so bypassing really doesn't seem necessary. (LS engines are a different story)
However- the water INSIDE the passenger cabin will slowly get to 180 degrees.

Closing both hoses- will keep the water inside the cabin from being heated.

Redvette2

Agree about two valves. I tried one valve and could feel the heat going into the other heater core hose. Now I use two valves and have no issues with overheating or the defroster as the top is never down.

kodpkd

The expansion tank is the one thing I wonder about. The valve I installed, is in the hose that runs from the engine to the lower heater core connection. The coolant can still expand into the expansion tank. What I don't understand, even with a "normal" system, there isn't a hose that runs FROM the expansion tank back to the radiator. The hose that connects to the top of the radiator, enters the expansion tank above the level of coolant, so coolant can expand into the tank but not the other direction, unless the tank is overflowing. Maybe that's the way it works. Does the coolant mix between the two large 2" hoses and the heater hoses at the water pump? The coolant running through the heater core has to be one way. Confusing!
Like mentioned, the 68 doesn't have a vacuum or manual controlled heater shutoff valve.

Redvette2

Couldn't you just put the valve on the hose between the expansion tank "tee" connection and the heater core inlet? Then the other valve could go on the return line which does not go to the tank.

Rescue Rogers

I'll look again tomorrow but i thought it was inline and flowed from the pump to the tank, as it expanded it pushied up into the tank. Past the tank goes through the heater core....

kodpkd

The diagram has the flow going from the pump nonstop to the lower heater core connection, through the core to the expansion tank. This would make the hose from the pump, through the core, act as a single hose all the way to the tank.

Dodosmike

I bought my 78 in 2006 or so. Put a 1/4 turn ball valve in it the spring of 2007. Sold the car in July 2020. It had been shut off that entire time. I literally never touched it. I even took the handle off so it’d look a little neater in the engine bay. Never an issue.

New owner opened it up and it poured heat out into the car. He turned it back off and said “I see why you had it shut off”.

bigvette1

No extra cooling pressures with closing both hoses off? Thx