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Do I need a heater control valve? Can't I just let the coolant flow through the heater core, since the hot air coming into the cockpit is controlled by a vacuum operated door. Isn't it so that when the "Heat" is off, the door is closed, and no heat enters the cockpit? Why bother with a valve that shuts off coolant thru the heater core, leaving it all wet and more likely to corrode? So why not have coolant flowing thru the core all the time?
When my '86 heater control valve began leaking several years ago, on advice i found right here on this forum i eliminated it.
I put a plug in the vacuum line and have not missed it at all. I used straight hose.
why not have coolant flowing thru the core all the time?
Exactly. WHY NOT? GM figured it out (eventually) on the later C4's and eliminated the valve. The blendair door, if adjusted properly should completely seal off heated air from the incoming "vent" air. Ya don't need the valve and GM should have never complicated a simple situation by putting one in there.
Are you confident there is a complete shut-off of the air flow thru the heater core when the temp. lever is in the "Cool" position? Is the heater duct work in the pre-'88 the same as the post-'88? GM could have saved quite a few nickles by eliminating that heater shut-off valve. I found that the Four-Seasons 74800 heater shut-off valve is an excellent, and cheap alternative to the original octopus!
(The heater core will be "wet" regardless of whether coolant is flowing thru it or not.)
From: Freedom is never more than one generation away from extinction.
St. Jude '03 thru '24
IMHO the best thing you can do is eliminate this valve.
The cabin temperature benefits are minimal.
But the longevity of the heater core is secured by the continuous flow of water.
The biggest problem with getting "hot" vent air, is the fact that the entire heater/blower box (and 1/2 the intake plenum) is sitting inside the engine compartment....which is HOT. In fact, one huge aspect of the heater box is facing and right next to the exhaust manifold. So you blow ambient air through a box that's probably 150˚, and it's going to warm the air up...whether coolant is flowing into a radiator in an adjacent compartment of that box, or not.
In my experience, if your blend air door is adjusted to close all the way, it won't make any diff to your vent temps if water is moving through your heater core or not.
.
Last edited by Tom400CFI; Aug 27, 2018 at 11:36 PM.
Are you confident there is a complete shut-off of the air flow thru the heater core when the temp. lever is in the "Cool" position? Is the heater duct work in the pre-'88 the same as the post-'88? GM could have saved quite a few nickles by eliminating that heater shut-off valve. I found that the Four-Seasons 74800 heater shut-off valve is an excellent, and cheap alternative to the original octopus!
(The heater core will be "wet" regardless of whether coolant is flowing thru it or not.)
Ha! Yeah, of course, but I meant when not in use, during the summer let's say, with the valve closed, the core just sits there static, damp, waiting for the blessed flow of coolant. That's a cause for corrsion, sure thing. I used to work on small gas engine equipment for Sears. People with generators mostly, but other stuff, snow blowers, another one, who never ran them periodically... moisture would develop in the float bowls, and wallah! Corrosion set in. Owners would say, "how could this thing be broken, I never use it!" Ha!
About the duct work and all that.... tested things... like others, valve not necessary. That's Good, because mine is toast!
Oh! Test: Turned on Heat. Moved lever to full hot.. Good. Moved lever to cold. Good. Moved lever to middle. Good. Turned on A/C with lever in cold position. I wanted to see if there was any effect on the cold air temp. None.
IMHO the best thing you can do is eliminate this valve.
The cabin temperature benefits are minimal.
But the longevity of the heater core is secured by the continuous flow of water.
Exactly! What I'm Sayin'! If you don't move it etc...
When my '86 heater control valve began leaking several years ago, on advice i found right here on this forum i eliminated it.
I put a plug in the vacuum line and have not missed it at all. I used straight hose.
I just re-did my entire cooling system, T-Stat, All Hoses (Cool Blue! from Continental/GoodYear), Sensors, relay, cap... everything but the water pump... oh... and the only hose I didn't replace yet, the 3/4" hose from pipe to pump. I'll get that whenever, if ever,I do the pump. Never know! Pump might last forever... When I flush the system,or whenever whatever, I'll get rid of the pipe.
Do I need a heater control valve? Can't I just let the coolant flow through the heater core, since the hot air coming into the cockpit is controlled by a vacuum operated door. Isn't it so that when the "Heat" is off, the door is closed, and no heat enters the cockpit? Why bother with a valve that shuts off coolant thru the heater core, leaving it all wet and more likely to corrode? So why not have coolant flowing thru the core all the time?
John
The correct corrosion inhibitor should take care of any core rust issues. The downside of no heater valve is that the heater core is pressurised whenever the engine is running (even in warm weather), reducing the time before one day it eventually starts leaking.
With or without that valve, the heater core is still pressurized. Blocking one side doesn't stop that. I have a manual valve in my '90 to block the hot water flow during the summer and switched to a 7lb cap to keep pressure relatively low. I also set the fans to come on at 200F so it never gets that hot. The trouble with relying on the blend doors is that the foam seals deteriorate and let hot air past in the summer months.
Can someone confirm... does the heater valve OPEN or CLOSE when the vacuum port is capped off?
I'd like to keep it in there, but would like for it to stay open at all time. The answer I'm hoping to hear is that it's open by default, closed when it gets engine vacuum (this means I can cap it off and it will flow through continuously).
If that valve works you're better off letting it continue to work, sitting in one position for extended periods isn't likely doing it any favors.
I'm an AC **** and I don't imagine the 40 year old foam in the HVAC system seals as well as it once did on top of R134 so I coughed up the money
to replace mine for the sake of the best AC I could get out of it(which is pretty good). Continuous flow is likely better for the heater core in the long run
but I suspect when GM removed the valve there was some change to the HVAC system, better sealing, a higher capacity AC, something.
It's not like they just started engineering HVAC systems the week before these were made...
Do I need a heater control valve?
The biggest problem with getting "hot" vent air, is the fact that the entire heater/blower box (and 1/2 the intake plenum) is sitting inside the engine compartment....which is HOT. In fact, one huge aspect of the heater box is facing and right next to the exhaust manifold. So you blow ambient air through a box that's probably 150˚, and it's going to warm the air up...whether coolant is flowing into a radiator in an adjacent compartment of that box, or not.
