Thermostatic valve in air cleaner test

[Tim Donahoe]

Hello, all. Has anyone figured out a way to check to see if the thermostatic valve in the air cleaner is actually working?

I have a 1974 Super Beetle with the paper-element air cleaner. All the vacuum hoses are connected, as well as, the pre-heater hose. The thing is, I don't really know if the valve that allows vacuum to the control flap is actually working after 38 years. I assume this valve (located in the center of the air cleaner with a vacuum hose attached to the left side of it from the manifold, and one attached from the right side of it to the flap) is heat-sensitive and allows the vacuum to pass through it (and on to the flap to open or close it), according to the temperature of the air that's passing through the air cleaner.

I'm installing new (old but good) thermostatically controlled flaps in the fan housing next Friday, and then I'll have that part of the warm-up taken care of. But it would be nice to know that the thermo valve in the air cleaner that operates the pre-heat air to the carb is actually working, also.

Any tests that I can do to check this out?

Tim

[Tim Donahoe]

Funny. Twenty-six people have read the above post, and not a single one has apparently ever tested to see if their thermostatic valve in the air cleaner really works.

Tim

[mrbigmax]

The last page of this post has what you are looking for.
http://www.thesamba.com/vw/forum/viewtopic.php?t=279958&postdays=0&postorder=asc&start=0

[Tim Donahoe]

Thanks, mrbig. I didn't realize that the thermo valve (stuck open) could be the source of a vacuum leak.

Good to know.

Tim

[djkeev]

[Boble]

Actually you can check it working by looking at this little indicator. It's an extention of the shaft holding the flap.

In cold weather it should be up at an angle. When the engine is warmed up or if the weather is warm, it should be horizontal (flap closed, carburetor sucking non-preheated air directly through the intake).

[75smith]

[Tim Donahoe]

Dave, sorry you were one of the "Twenty-Six". You made a good point, however. It's better to have good advice than none at all.

I have noticed in many of the subjects that a great many people read the posts--but few actually offer advice. Sometimes it is a newbie with a very simple question--and yet I only see Cusser, Ashman, Glen, and a few others (sorry if I missed someone) actually take the time to help out. My point was to get some of the quiet ones to speak up--not to rake anyone out.

Bob--I saw that little hinge post and figured it would move. But It was 68 degrees Fahrenheit here in Northern California today, and the pin didn't budge. I'll check it in the morning when it's closer to 32 degrees.

Tim

[Boble]

[djkeev]

You are only talking temperature in the 70’s, low 80's.....

[Tim Donahoe]

Well, I started the engine the morning when it was 36 degrees F outside. The flap didn't move a bit at "fast" idle.

Tim

[djkeev]

['69Custom]

[Tim Donahoe]

dj, at 36 degrees Fahrenheit, the valve remained closed and would not allow warm air into the air cleaner.

Tim

[CarlIseminger]

I will admit that I am one who reads LOTS of posts just to gather information. I may not ever use the information, but sometimes, when something is wrong with my bug, I will remember that there was a post about this very problem and go search for it. Saved me many times.

[Boble]

[Tim Donahoe]

bob, thanks for the advice.

I pulled the right vacuum hose from the thermostatic valve (the brass one) and sucked hard. The flap moved a tiny bit. I will next unhook both vacuum hoses from the thermostatic valve and temporarily splice them together with my vacuum tester tri-fitting. Then I'll start the engine and see what the flap does at different rpms. If the flap opens all the way at the higher rpms, I can assume that the flap is okay. If not, I will try to lube it--although it seems it's all plastic. If that doesn't work, I'll have to find one in the Samba Clasifieds, I guess.

The vacuum hoses are not regular vacuum hose, by the way. They're black rubber--not like the the cloth-webbed vacuum hose that, say, I use for my SVDA distributor-to-carb vacuum line. But the black hoses are in good shape--but seem more pliable (maybe more prone to collapse?) However, I have seen this same black rubber vacuum hose on many photos of bug engines, using the same air cleaner that I have (which is the paper-element one).

The diagram you showed in your post is still an oil-bath model, but the workings look to be the same as the paper-element one that I have.

I'll test again tomorrow.

Tim

[Boble]

[Gitchigumi]

I was one of the 26 or so that viewed this post with interest as I had one functioning themostate but a functing vac can. I decided to see if I could take one apart and here is what I found.

Two parts screw out. Under the large brass insert is a small plastic check valve that sits atop a bi-metal strip with the number 20 on it. I suspect 20 stands for 20 deg.C. Under the brass tube which unscrews, is a different check valve which stradles the other end of the bi-metal strip and is made of rubber with a plastic end that sits in the brass tube. Do not try and remove this one as it appears to have been installed before the two halves of the thermostat were put to-gether.

In my case the brass tube one was coated with hardened gunk and would not float freely. A bit of WD-40 and compressed air cleaned it up nicely. I suspect the problem with most "non-functioning" thermostats is simply dirt in the system after 40 years.

You will also see from the photos, a very small hole in the top of the thermostat housing on the brass tube side. This is a bleeder hole that allows air back into the vac can once vacuum is no longer applied, allowing the flapper to release and close of the warm air inlet and allow cool air to enter the carb.

I sprayed WD-40 in both ends of the thermostat and air dried it to make sure it was nice and clean.

The brass tube screws back in pretty much flush - see pictures. You should be able to detect movement of the little check valve by blowing and sucking on it.

The larger check valve with the ball, screws in leaving about 5 threads still showing - see pictures. Assuming you are working where it is above 20C that bi-metal strip should not be flexed but flat. The check valve ball sits open just a bit at this point, allowing air to be draw through the hole in the check valve and not through the brass tube check valve. I adjusted it by screwing it in until you can only see 2 threads. I blocked off the small bleeder hole with my finger and sucked on the black plastic tube. You should be able to draw air through the brass tube. I then unscrewed the check valve body, half a turn at a time until I began to draw air freely through the hole in the ball check valve. At this point the vacuum is broken to the vac can. You will sense the check valve ball vibrating as you get to this point. I back it out just past this point.

I suspect the valve works like this:

When the temp is below 20C or so, the bi-metal strip flexes just enough to close the ball check valve. As the brass tube valve floats freely, it is sucked open allowing vacuum to be applied to the vac can, closing the cool air intake and opening the warm air intake. Once the bi-metal strip reaches 20C or so it returns to normal out opening the ball check valve and breaking the vacuum link to the vac can, allowing the brass tube check valve to fall into the brass tube. Because this valve is free floating, air slowly re-enters the vac can via the little bleeder hole allowing the flap to close over the warm air intake and open the cool one.

In any event, after cleaning and adjusting as described my flapper works like it should, and that is all that matters to me.

New thermostats should still available through your local Volkswagen dealer for about $100.00 plus tax - I checked with mine. But try cleaning and re-adjusting to save yourself a few bucks.

[Gitchigumi]

The above is a repost which is I believe, more correct than my original attempt.