Cable Operated Heater Valve won't stay shut

[svenedin]

This concerns the later cable-operated type heater valve.

When my engine was rebuilt over the Winter of 2024/2025 I fitted a new cable-operated heater valve and a new cable. This type: https://www.morrisminorspares.com/cooli ... s-p1238742

I have found that the heater valve will not stay in the off position when out driving. It will stay off with the car parked and the engine off. The wire runs through the cable so smoothly and the valve operates with so little resistance that just the vibration of the engine is enough to open the valve.

Of course one solution is to just set the heater box air baffle in the car to off. In that position not much heat gets out. Another is to put a clothes peg on the heater valve control in the same way as holding out the choke knob.

Has anybody had the same issue and what did they do to correct it? The cable is a single wire and trying to put a twist in the end has not achieved anything. I resorted to using a clothes peg. A possible method might be to crush the cable outer with pliers to create resistance to movement of the inner wire but this seems a bit brutal and easy to go too far and render the cable useless.


Stephen

[bobtail4x4]

just about to fit a cable controlled valve to mine,

did you use a "twist" lock cable?
that should keep it closed,

[svenedin]

No I used the cable supplied with the valve as per the link. It is not twist-to-lock.

Stephen

[svenedin]

I recalled there was a reader's letters tip on this and I have now found it in Minor Matters 2023 Volume 44 number 4 page 13. The reader from Vienna, Mr Felix Weschitz suggested making a spring clip from a bent paperclip. I shall experiment.....

Stephen

[bobtail4x4]

https://www.ebay.co.uk/itm/357124542303

[svenedin]

https://www.ebay.co.uk/itm/357124542303

Thanks but that isn't the correct cable. The correct cable says "Push Heater" on the knob.

Stephen

[bobtail4x4]

I see your point

[Bill_qaz]

Had the same issue with replacement valve due to leaking not long after I bought the car, it would not stop heat although checked and fully closing. Just fitted alloy valve cover so needed one of the offset type from ESM fitted it and it works perfectly, full cold heater when off and nice and warm when on.

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[svenedin]

Thanks Bill.

I have exactly the same type of offset cable-operated valve from ESM but it will not stay in the off position. In my photo it is in the off position but if I go out for a drive the valve opens. Now I know there are many people who advocate having the heater valve open at all times to improve the coolant circulation around the back of the engine but if like me you travel to hot places in Summer it really isn't pleasant to have excess heat in the cabin.

Stephen

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[Bill_qaz]

I don't think thats fully closed in your picture the arm pulls up to the dome when fully shut. Adjust your cable to pull it more, from memory the last bit has a little resistance which i assume is compressing the rubber inside to give full seal.

[svenedin]

Ok adjusted. Valve does not open just with the engine running at idle whilst I watch (engine fully up to temperature). I’m going for a 40 mile drive now so I’ll see what happens.


Stephen

[svenedin]

The valve stayed closed for about 30 minutes of driving but then opened itself as usual. In fact this was quite welcome because top-down motoring at night in mid-October is quite chilly. I'll try a new valve when I get round to it.

Stephen

[Bill_qaz]

I find it hard to believe water pressure is pushing the valve open and the coolant system not overpressuring. It's more likley to be vibration causing the arm or cable to vibrate and partly open.
Do you see the heater control push move. Try hanging a small weight on the cable to change the harmonic, so if its vibration it will effect it. Or fit a light spring to hold closed, the cable would easily overcome it when opening it.

[svenedin]

The valve didn't open until I was on a dual carriageway doing about 55/60 mph and yes the heater control knob had moved forwards. I think it's bumps in the road that jar the valve and cause it to open. Once it starts to open it soon opens fully. It's odd because with the old valve I had a while ago, I could actually set it wherever I wanted (off, partly open, fully open) and it would stay exactly where it was set.

I found another valve in the garage and this one will happily sit and stay in the off position with no cable attached. The one on the car at the moment will not stay in the off position with no cable attached so I think it may actually be faulty.

Stephen

[Bill_qaz]

The valve didn't open until I was on a dual carriageway doing about 55/60 mph and yes the heater control knob had moved forwards. I think it's bumps in the road that jar the valve and cause it to open. Once it starts to open it soon opens fully. It's odd because with the old valve I had a while ago, I could actually set it wherever I wanted (off, partly open, fully open) and it would stay exactly where it was set.

I found another valve in the garage and this one will happily sit and stay in the off position with no cable attached. The one on the car at the moment will not stay in the off position with no cable attached so I think it may actually be faulty.

Stephen

Yes as I found the last part of closing feel like its compressing rubber, a seal maybe, possibly it will bed but not noticed mine switching back to on. Why don't you try the light spring before you change the valve?

[svenedin]

Yes, I'll have a look for a suitable light spring. For now, I have found the by holding the heater valve control knob and preventing it from turning whilst tightening the back nut seems to introduce some more friction to the movement of the inner cable. This may be sufficient. A road test will be needed.

Stephen

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[svenedin]

I ordered a new valve and it arrived this morning. It is different. I seems sprung to want to stay shut so I shall just go ahead and fit it this week.

I ordered a couple of spare gaskets and to my surprise I received 3 packets of 117 gaskets each. 351 gaskets rather than 2

I phoned ESM of course and said I would send the vast horde of gaskets back. Apparently new staff in the packing department.

Stephen

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[Bill_qaz]

So is you picture of the new valve shown in closed or partially closed? As the arm is not fully upto the housing.

[svenedin]

So is you picture of the new valve shown in closed or partially closed? As the arm is not fully upto the housing.

In my picture it is resting almost completely shut. If I blow into the valve there is very little flow.

I wouldn't go to the trouble of changing the valve if it wasn't for the fact that there are a couple of other jobs I want to do with the coolant partially drained. Changing to a hotter 88 C Winter thermostat and replacing the heater return pipe for one I have refurbished.

Stephen

[Bill_qaz]

Be interesting to see if the replacement acts any differently