Heater Valve / Coolant Flow

[lobf]

Hey folks- 

 

Just finished a heater box rebuild last week, and I've got a question about the coolant flow. 

 

If I shut my heater valve, I still get hot air coming out of the box. I accidentally had the valve side unattached to any hoses while I was testing things out, and water was still being pushed through the core from the "outlet" side and coming out of the valve side. (Hope this makes sense.) 

 

Is this normal? Would you actually need two heater valves to stop flow of hot water through the core? Doesn't seem to make sense to me- how are you supposed to get regular cool air blowing in from outside? 

 

Thanks in advance for your help! 

[halboyles]

Normally with the heater valve closed the inherent back pressure from a pressurized coolant system wouldn't be able to flow "backwards" out of the valve side.  So if you are still getting heat with the valve "closed" then either the valve isn't really closed and/or the fresh air flap is not opening.  Some coolant is always moving through the heater core due to a small opening in the valve even when closed but if the flap is open to provide fresh air the heat shouldn't be that noticeable.  

[PaulTWinterton]

Does not make sense.  Valved side of the heater core gets coolant from the engine.  It is circulated through the heater core and out the other side, back to the engine. 

If you close the valve, the coolant in the heater cools and you will no longer get hot air in the cabin.  The only mistakes you can make are wrongly connecting the cable, or reversing the hoses in the engine.

 

Pictures?

[Simeon]

I thought I had read somewhere that the 'later' valve always has a small flow through when closed. 

[PaulTWinterton]

2 hours ago, Simeon said:

I thought I had read somewhere that the 'later' valve always has a small flow through when closed. 

 

Yes, I believe it's minimal, but lobf appears to have backward flow, if I read his post correctly.

[lobf]

14 hours ago, PaulTWinterton said:

 

Yes, I believe it's minimal, but lobf appears to have backward flow, if I read his post correctly.

 

Yeah, it looked like I had backwards flow. LIke I said, I took the hose off the inlet side, and water was being pushed out from the opposite direction. 

 

My box rebuild did have one snag- the cool air flap cable seems to be stuck- it seems like it won't open. Certainly that would help cool the core a bit, but I'm getting *real* hot air out of that box. 

[OriginalOwner]

I can see how you could get a bit of backward flow, such might not be entirely unreasonable.  And I'm thinking it is more back"pressure" pushback from the water pump, rather than an actual "flow" path.

 

Anyway, I recall that I have always had some amount of coolant flow through the heater core, which means the heater core is always hot ...... and any air which gets past the heater box flap(s) is going to be hot.

 

That's why I have always liked the wind wings so much, they are an excellent cabin temperature modulator.

 

Cheers,

 

Carl

 

 

[Simeon]

Just re-read the OP. If the valve and core were disconnected from the engine then you will always get flow in the opposite direction since the cooling system will be at a higher pressure than atmospheric. When fully connected the water is at the same pressure either side of the valve through the rest of the system. 

 

The system works by a combination of percolation due to temperature differentials between the hot input and 'cold' return along with a slight reduction in pressure on the return side where it runs into the back of the water pump. The coolant is not exactly racing through the heater core. The valve only needs to provide a bit of obstruction to this flow to cut off the heat. 

[Chris_B]

There shouldn't be any appreciable amount of coolant flowing through your heater core when the valve is closed. Is it possible that you mounted the lever on the valve upside down (so it would be open when control is in the closed position (this is possible on at least one version of the valve).

[John76]

When the heater valve is assembled correctly, the water flow (in the arrow direction) presses the valve cylinder against the valve seat. This creates a tight seal when the valve is closed, although there is still a small opening to allow a small amount of flow at all times. I think this is to minimize any air pockets in the core?

If you attach a hose to flush the core from the outlet side, the water pressure will unseat the heater valve and you will get flow even when the valve is closed. The valve is held against the seat by the wire spring, which will yield to any pressure in the reverse direction.

I discovered this when I was pressure testing my heater core after rebuilding the valve. At first, I had it assembled wrong, and water was flowing past the closed valve in the proper direction, but was sealed in the reverse direction.

[02Les]

17 hours ago, John76 said:

When the heater valve is assembled correctly, the water flow (in the arrow direction) presses the valve cylinder against the valve seat. This creates a tight seal when the valve is closed, although there is still a small opening to allow a small amount of flow at all times. I think this is to minimize any air pockets in the core?

I beg to differ. I have the "all brass" valve and when it is closed nothing gets through. When you begin to open it, the slit appears and starts to let coolant through.

I believe the slits (inlet & outlet sides) prevent a surge when opening the valve to save the Heater core from a shock pressure and likewise when closing to prevent a shock to the valve or whatever may be sensitive upstream.

[John76]

Did you try to flow water through the valve in the reverse direction? I'll bet water gets though, and not just a trickle through the bleed slot.

[02Les]

8 hours ago, John76 said:

Did you try to flow water through the valve in the reverse direction? I'll bet water gets though, and not just a trickle through the bleed slot.

It's tight shut both ways when I blow into it. I'll see if I can hook it up to the garden hose to try. I had to clear out a little crud at the ends of the slot in the cover plate, so that helped. Once the innards move a wee bit, flow will start.

I have no clue if the "later" heath robinson style performs the same.

[jgerock]

Here is the valve in my 73tii.  Looks like the channel goes around it to allow a little flow of coolant.