Thermostatic valve in air cleaner test

[AMS_Dizz]

I use my ultrasonic cleaner to remove any gunk from the thermostat. I just use water with a little degreaser, then blow air into the hole to remove any remaining water.

[tzepesh]

A note on ultrasonic cleaner: pay attention what liquid you are using. There is a rubber valve inside (orange in one of the photos) and it may be affected.
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'74 1303S, L98B Viperngrun (extra glitter), German Look
'64 1200, Sea Blue, under restoration

[vamram]

[tzepesh]

That is a very good idea! I will look for somebody who may help.
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'74 1303S, L98B Viperngrun (extra glitter), German Look
'64 1200, Sea Blue, under restoration

[busdaddy]

Sounds like a job for an ultrasonic cleaner.
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[tzepesh]

I will let you know, I will try with the other one. I will be careful with compressed air in those tiny nipples, there is not much air passing anyway. I will try to do all through the large "jet" hole, but it will take me some time, now I'm helping a friend with his bug.
I managed to glue back this one and it is not leaking vacum (with all holes closed)
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'74 1303S, L98B Viperngrun (extra glitter), German Look
'64 1200, Sea Blue, under restoration

[vamram]

Great write-up, Tzepesh. Do you think these can be properly cleaned w/out taking them apart? Just alternating WD-40, brake cleaner and possibly compressed air thru the stems/nipples?
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[tzepesh]

I took apart one of the two thermostatic valves Ihad, to understand ow it works and what the issue my be.
My observations: the vacuum leak will be there all the time, there is nothing to block off the tiny hole in the housing. So the carb must deal with that, and seems that it will affect idle tuning, as the carb will expect to be there.

The small pistion inside was moving very hard. It passes through a rubber boot or valve. I think the tube was also clogged. So I blew it with brake cleaner several times, and not it is moving easily and it blocks or releases path for vacuum. I think this is the issue with all units, as stated in this topic: it gets clogged with oil residues from air filter (the crankcase venting) and it becomes stuck. You need to be very persistent to make it move, alternate brake cleaner with WD40.

The bi-metal part that activates/decativates vacuum can be adjusted by the large "jet" with plastic ball. I have not atemped it yet, so no advice here.

It's easy to work with it dismantled, hopefully I can get it glued back and no leak. Otherwise I will get to cleaning the other unit, without tearing it apart.
_________________
'74 1303S, L98B Viperngrun (extra glitter), German Look
'64 1200, Sea Blue, under restoration

[busdaddy]

I thought page two covered the function really well, yours sonds like it's gunked up inside, or needs adjustement since it's in hot mode even when cold.
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[vamram]

Bit of a wild guess here Tzepesh. I think when cold the bi-metal strip contracts just enough on the side going to the air cleaner snout to allow vacuum to open the diaphragm. As the air heats up, the metal strip expands, closing the port and the snout diaphragm.

I suppose you could test it w/the car running. Pull the intake vacuum hose from the top of the air filter and plug it w/your finger. If there's a vacuum leak, this should immediately affect your idle. I think.
_________________
"Men are qualified for civil liberty in exact proportion to their disposition
to put moral chains upon their own appetites. -Edmund Burke
“If something cannot go on forever, it will stop.”
Stop Russian-Soviet Aggression!!

'74 Super 9/16 - present, in refurb process.
'73 Super - 6/18 - Present - Daily Driver!
'75 Super Le Grande...languishing since 2022.
Click to view image
Save the Supers!!

[tzepesh]

Reviving this old thread. It is still not clear how this small thermostat is suppoed to work. My concern is that when I suck on the plastic pipe, there is air coming in from the bleeding hole on the back. I expected that air would be coming in through that hole only to remove vacuum when the flap needs to close. I never get to have the vacuum from the plastic tube to go to the brass tube...
Please educate me some more on the topic. I would rather have the hot air circuit not working than struggling with vacuum loss and not being able to tune the carb...
_________________
'74 1303S, L98B Viperngrun (extra glitter), German Look
'64 1200, Sea Blue, under restoration

[APPLEGREENVW]

[Boble]

Hi,

The piston valve that actually controls vacuum to the air filter is not adjustable.

The ball valve is, though.

You want it to open at around 77 F (25 Celsius). I think your description above makes sense. Like this:

1. The whole unit should be at 77 F (25 Celsius). Give it enough time to reach that temp
2. Block the piston valve tube (brass) and the "small bleeding whole" beside the ball valve screw on top
3. Suck on the plastic tube with your mouth
2. Adjust the ball valve screw until you find the point where it just opens

I cannot believe that it is super critical if you don't hit exactly 77 F, after all it just regulates the air temp to the carb.

[APPLEGREENVW]

Boble
How do you adjust your thermostatic valve?
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02/76 Beetle sedan

[Boble]

Curious about what's inside this fella, I cut one open some time ago. As you can see below, there are TWO valves inside:

1. A piston valve that controls the vacuum flow to the air filter flap

2. A ball valve that opens up when warm and thus "zero'ing" the vacuum.

There are "no serviceable parts inside". If it don't work it's probably just dirt in there. Soak in solvent and blow though it with compressed air. Test with cold air (fridge) and warm air (hair dryer).

[APPLEGREENVW]

[Tim Donahoe]

The easiest way to test the air cleaner thermostatic valve on the paper-element air cleaners is this:

Make sure the ambient temperature is under 70 degrees Fahrenheit. Look at the air cleaner snorkel, and you will see a small hinge pin (my wife is pointing at it). Start the engine, and look at the pin. If cool enough outside, the line in the hinge pin will move to the vertical. This means the flap on the snorkel has opened to allow for pre-heated air o enter the air cleaner.

The thermostatic valve will operate the snorkel flap anywhere between full open and full closed, according to the ambient temperature.

If the line on the hinge pin stays horizontal on cold morning start ups, then your thermostatic valve is shot, or your vacuum is not hooked up correctly.

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[bluebus86]

has a small leak thru the vent hole when warm, but not after I frooze it via the tiny hole in the body of the unit once warmed up, the hole is what allows the vacuum to be released allowing the hot air flap to return to warm running position. so yes the unit does have a pin hole leak when warmed, and it needs that leak to release the flap to return to warm position.

Its ok, mine is working.
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[busdaddy]

It's been a few years since I dismantled one of those valves and studied them but I do recall it being much more complex than it outwardly appears.
Yes it does direct vacuum to the dashpot that opens the heat flap when it's cold in the inlet. And when it's finally warm enough it cuts off the vacuum and allows air to return through the hose to the dashpot so it can close.
But I seem to recall it also becomes a pseudo idle compensator when it's warm by creating a vacuum leak and leaning the mixture slightly.

There should be no vacuum leak on the manifold port nipple when it's below the opening temp marked on the housing (usually ~90*F). The rubber seal on the end of the bimetal strip is likely petrified.
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[Tim Donahoe]

I don't know al lot about the valve. When mine failed to open four years ago, I tried to clean and refurbish it, but I ended up buying a new one.

I seem to remember a bi-metallic spring inside the unit, and most of all, I remember that if the unit fails in the open position, it can be a source for a vacuum leak. This vacuum leak is often hard to find, since most owners don't realize that a faulty thermostatic valve in the plastic air cleaners can be the culprit.

If your valve isn't working, I'd just get a new one from RockAuto (the Rabbit ones are the same, so look under Rabbit for parts).

As far as the hole in the thermostat is concerned, I can't remember it's function exactly, but I seem to recall that it has something to do--at some point--with letting off pressure within the unit itself. So this hole may be the source for the vacuum leak I heard of when the unit does fail.

You can always plug the line, or the male nipple on the manifold, and see if your vacuum leak goes away. At the least, you'll know it's not the valve.

Tim
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Richard O'Brien