Cooling Flaps return spring.

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kaddy
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Joined: 25th January 2011 - 12:39am

Cooling Flaps return spring.

Post by kaddy » 15th March 2019 - 5:21pm

Quick question regarding the return spring.

Exactly where does the return spring attach to. The door flap end is straight forward.
But where at the thermostat top link plate area is it attached.

Is this spring absolutely necessary, given that the thermostat, expands and contracts,
effectively opening and closing the flaps. So where does the spring come into effect.

Thanks
Tim

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937carrera
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Location: North Yorkshire

Re: Cooling Flaps return spring.

Post by 937carrera » 15th March 2019 - 10:12pm

Are they like type 4 ?

Spring forces the flaps open, cable from thermostat pulls them closed when the engine is cool.
David
1974 412LS Variant
1973 412LE 4 door Fastback / Saloon

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purplepeter
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Location: Bath, Avon

Re: Cooling Flaps return spring.

Post by purplepeter » 15th March 2019 - 10:38pm

Yes Kaddy, It's vital!
Small hook on spring goes through a hole in Right hand flap, Bigger hook goes onto the relay lever (fairly self explanatory when you see how it lines up)
http://www.hallvw.clara.co.uk/type3/T3pbo/T3pb1-37c.htm

kaddy
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Joined: 25th January 2011 - 12:39am

Re: Cooling Flaps return spring.

Post by kaddy » 15th March 2019 - 11:51pm

So spring pulls them closed, and thermostat pushes them open.

But thermostat also pulls them closed when its cool and contracting ??

Academic because I dont have one on either engine. How strong is it,

is it stronger than a carb pull down spring?

Anyone ever arrive at a fix with an alternative.

Thanks

kaddy
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Joined: 25th January 2011 - 12:39am

Re: Cooling Flaps return spring.

Post by kaddy » 15th March 2019 - 11:54pm

Is the same spring as used in a type 1 engine at the back of the cooling tower.

kaddy
Posts: 537
Joined: 25th January 2011 - 12:39am

Re: Cooling Flaps return spring.

Post by kaddy » 16th March 2019 - 12:36am

Good article here that I have just found
https://www.thesamba.com/vw/forum/viewt ... mp&start=0

Clearly shows the connections of the substantial spring. But the spring looks to be pulling
the flap open a bit. And the thermostat pushes it open.

Why the need for the 2?

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broady_6
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Re: Cooling Flaps return spring.

Post by broady_6 » 16th March 2019 - 8:02am

If the themostat fails then spring holds the flaps open. Its so important to get some cooling air to the engine, its better they're forced open in a failure situation. Your engine will become a paper weight very quickly if the flaps dont open. The spring is also a helper for the thermostat to get them open when all is alive and well
The sultan of swing

kaddy
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Joined: 25th January 2011 - 12:39am

Re: Cooling Flaps return spring.

Post by kaddy » 16th March 2019 - 8:57am

But couldn't you just set the same amount of opening on the flap,
with the connecting rod, and leave the spring off. Even with the thermostat in the cold position,
there is very little pressure from the spring, and the flap is adjusted with the horizontal rod
to maintain a small opening. Spring on or off wont change this setting.

Am I missing something here ??

kaddy
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Joined: 25th January 2011 - 12:39am

Re: Cooling Flaps return spring.

Post by kaddy » 16th March 2019 - 8:58am

As we say over here, I think this needs another coat of looking at :D

kaddy
Posts: 537
Joined: 25th January 2011 - 12:39am

Re: Cooling Flaps return spring.

Post by kaddy » 16th March 2019 - 9:11am

So basically the spring is for taking up the slackness of the connections of the flap to rod,
rod to lever arm, lever am to spring, and spring to flap, thereby maintaining connectivity
of all the important elements.

Makes perfect sense now, any vibration here could disconnect the flaps from the rod, and thereby
closing the shutters permanently regardless of a working thermostat or not. Spring stops this.

I think this sounds right.
Comments?

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937carrera
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Re: Cooling Flaps return spring.

Post by 937carrera » 16th March 2019 - 9:20am

You're missing the failsafe in the original design.

From the picture the type 3 has a rod, rather than a cable on the type 4, they work the same. There's still a difference though. Without the spring you are relying on the thermostat to push the flap open. With the spring, you are using the thermostat to close the flaps when the engine is cool.

In one mode the thermostat is compressing (pulling the flap against the spring), in the other it is expanding (pushing the rod). Sometimes things are just designed to work in one mode or the other.

I think you've got it now
David
1974 412LS Variant
1973 412LE 4 door Fastback / Saloon

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purplepeter
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Location: Bath, Avon

Re: Cooling Flaps return spring.

Post by purplepeter » 16th March 2019 - 9:37am

Although the normal fail position of the thermostat is for it to expand, it's perfectly possible for it to fail not fully open & for the bracket etc to get fouled up with oil/road grime etc, making it sticky.
The spring ensures that the flaps open fully whatever the condition of everything else
Just fit the sodding spring & have confidence that it'll do it's job!

kaddy
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Joined: 25th January 2011 - 12:39am

Re: Cooling Flaps return spring.

Post by kaddy » 16th March 2019 - 10:26am

There is no way the spring can fully open the flaps if the thermostat is stuck closed.
It will partially open.

I,d love to fit the sodding spring, if I had one. Thats why I,m asking these questions about the spring,
to find a work around.

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937carrera
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Location: North Yorkshire

Re: Cooling Flaps return spring.

Post by 937carrera » 16th March 2019 - 11:21am

Try one of these - it may need some fettling, but if you get it functioning then it's a proven solution for other type 3 owners - you're not the first person to have this problem

https://www.machine7.com/product.php?xProd=15119
David
1974 412LS Variant
1973 412LE 4 door Fastback / Saloon

kaddy
Posts: 537
Joined: 25th January 2011 - 12:39am

Re: Cooling Flaps return spring.

Post by kaddy » 16th March 2019 - 12:08pm

Yep. Just took a spring from a type 1 1600 engine I have.
And same amount of coils, so good to go, I,ll try it.

Result.

happy paddys weekend folks.

Tim

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purplepeter
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Location: Bath, Avon

Re: Cooling Flaps return spring.

Post by purplepeter » 16th March 2019 - 12:18pm

It's worth mentioning also that you must use the copper bellows type of thermostat, NOT the newer waxstat type, which fails by default in the closed position!

kaddy
Posts: 537
Joined: 25th January 2011 - 12:39am

Re: Cooling Flaps return spring.

Post by kaddy » 16th March 2019 - 12:52pm

Thanks, have fitted a good old school thermo. cant be doing with the new fang dangled tat :)

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broady_6
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Re: Cooling Flaps return spring.

Post by broady_6 » 16th March 2019 - 1:31pm

Happy St Irish Sunday, I had my fuzzy head last night so I wont be repeating that again this weekend.
The sultan of swing


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