Thermostat Question

I have a 1973 std beetle. The thermostat is frozen in the compressed (unexpanded) postion. I have an new one ordered; but, I don't understand the exact workings of this device. Does this unexpanded condition mean the blower doors are closed and thus cause overheating of the engine? After removing the thermostat mounting bolt, the unit was pulled up by the rod going to the doors. Since I can pull down and operate the doors, I assume they will be working fine with a new unit.

Am I correct in my assumptions?

Bob

Reply to
Bob Ullet
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have you confirmed that the unit is indeed in the collapsed condition when the engine is up to operating temps?

if it is indeed failed in the collapsed position, then yes...collapsed position is the closed(almost) position of the "flaps"....

excellent...that means the spring and linkages are in place....and the flaps are not rusted solid...

yes, you assumed correctly....

------------------- Chris Perdue

*All opinions are those of the author of this post* "Sometimes you're the windshield, sometimes you're the bug"
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Reply to
Chris Perdue

Yes-- I did test it in hot water and it doesn't expand at all. Since I could not see what was going on with the doors, I was not sure how it operated. Thanks all for the information. The new one should arrive by the end of the week.

Bob

Reply to
Bob Ullet

The thermostat is SUPPOSED to be stuck in the compressed position, it expands as it gets hotter. If it's "bad", it means it's puctured and it will then expand on it's own and stay expanded for the rest of it's life, to about 80-90% of it's maximum expanded lenght. Meaning, it's broken beyond repair.

How to test: Dip the thermostat in boiling water, it should start expanding almost immediately. Pull it out when you see it expand, no need to keep it in teh water for longer than intended. The designed expansion temperature is around 70-80 degrees (Celsius) depending on thermostat model (Yes you have two heat ranges to choose from, it's stamped on the thermostat bottom) and water boils at 100 Celsius.

So in theory, you may be able to "cook" a thermostat by overheating it in boiling water. (Highly unlikely)

Jan

Reply to
Jan Andersson

They don't fail in the collapsed position. It's designed to fail only in the "open" position, so that the engine won't overheat if the thermostat dies.

Jan

Reply to
Jan Andersson

Are you sure it's frozen? The only way to check is to look under there when the engine is hot and see if it has expanded.

Yes, the cooling is reatricted when the thermostat is compressed.

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----------------------------------------------- Jim Adney snipped-for-privacy@vwtype3.org Madison, WI 53711 USA

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Reply to
Jim Adney

KEYWORD: "designed"....and i agree with you...they don't....but sometimes they do(hows that for agreeing, yet not agreeing? LOL)...i actually have a "failed" one in my basement that will not expand...

------------------- Chris Perdue

*All opinions are those of the author of this post* "Sometimes you're the windshield, sometimes you're the bug"
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reply take your PANTS off
Reply to
Chris Perdue

That's what I always thought, too, but Bob Hoover claims that there are versions which actually DO fail in the collapsed state. I've never seen one of them. That would be a very bad design in my opinion.

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----------------------------------------------- Jim Adney snipped-for-privacy@vwtype3.org Madison, WI 53711 USA

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Reply to
Jim Adney

If you heated the water to boiling on the stove that would be a good test. If this was done with hot water from the tap, that's not going to be hot enough to expand the thermostat. Most water heaters are set for about 135-145F but the thermostat doesn't open until about 165F.

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----------------------------------------------- Jim Adney snipped-for-privacy@vwtype3.org Madison, WI 53711 USA

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Reply to
Jim Adney

I just bought a conversion kit with the new brass thermostat thats looks like a compressor safety valve. It has an external spring on it and looks nothing like the old bellows type of therostat. Guys will this one also fail in the expanded mode?? Eric 62 Ghia cab 68 bug cab

Reply to
Stutzsr

Yea, they are supposed to fail in the "fully open" position, but in fact I have yet to see any reach 100% open when punctured. They expand to some extent, like I said most go up to 80-90% open when punctured. I tested a handful of thermostats to get reliable data on this a few years ago.

The thermostat has VACUUM inside, plus a small amount of liquid that has a boiling temperature lower than water. When the thermostat warms up, the liquid starts to boil (even lower boiling temperature in vacuum) and the gases that evaoprate from it actually start to build PRESSURE inside the thermostat. Then when it cools down, the vapors condense back to liquid form and vacuum returns when it's cold. Beautiful closed system. When you punch a hole on it, you lose the vacuum and it expands some. But you can't get PRESSURE in there because it no longer is a closed system. Therefore, it won't be fully expanded. It gets soft and easy to move though, and the flap return spring would be able to pull it further open when installed in the engine.

Jan

Reply to
Jan Andersson

Speaking of thermostats,is there a way to use a T1 in a T4.Just 1 example of T4 parts that are NLA or very expensive.Steve

Reply to
Ilambert

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To All:

This was back when they introduced the 'Fresh Air' heating system. All the VW mechanics thought it was a dumb idea.

A related problem was that some of the bellows were not flexible; they would literally break apart along their inner folds. Any complaint of overheating, after checking the belt you'd check the thermostat.

When I wrote about that failure mode -- thirty years later -- several people said it was no longer true, that all the bellows they'd seen remained flexible and always failed open. Someone even sacrificed a brand new thermostat as a test (this was probably eight or ten years ago). Punctured, it failed open. I was glad to hear it but I still had several old thermostats in the junk box, failed closed and hard as a brick. You could boil them all day long and they stayed the same size. Corrosion or metallurgy may have played a role here but the fact is the thing was U/S and in the compressed position.

Liv & lurn

-Bob Hoover

Reply to
Veeduber

Thanks Jim. I was trying to use only tap water. It wasn't hot enough. After heating some water it expanded at 150 deg F.

Last week after driving my bug for about 15 miles, I looked under to check the thermostat of expansion. It appeared to be totally collapsed. The engine was still running and lots of heat blowing onto it. The outside temperature was in the low 50's. Is this normal? Just looking at how it is mounted, it appears that if your are going down the road the air should keep it too cool to expand. Maybe if you are in summer heat it will open?

Bob

Reply to
Bob Ullet

not a bolt-on swap as I recall. But I guess it's doable.

Jan

Reply to
Jan Andersson

The thermostat location does NOT see any airflow other than the air coming from the engine. Unless your lower engine tin is missing.

This is a perfect example of why you need a thermostat, even when you checked it with the engine running, it was keeping the flaps partially closed. Your engine was NOT running warm enough for the thermostat to provide maximum cooling. That's why it's there, to *control* engine temperature. Not just to maximize cooling. Without one, you will OVERCOOL the engine and that would result in accelerated wear. Among other things that may be just as hard to notice like rougher running and poor mileage. The aircooled engine is a carefully designed entity, and temperature control is critical for everything to work optimally. Lots, and I mean LOTS of parts rely on controlled thermal expansion and this has to happen at a certain RATE too. Not too fast, not too slow. But in synch with the rest of the engine. There's a mixture of steel and aluminum parts in there, materials which have very different thermal expansion rates. If you modify the cooling system somehow, you are likely to disturb this balance and certain parts will expand faster than their neighbor. Not good. Not only will this result in wear, but also tear. (Head studs pulling out of the case come to mind)

Jan

Reply to
Jan Andersson

There should be some sheet metal under the thermostat. That "shield" should be closed at the front and bottom, meaning that it directs the hot air down around the thermostat and out the rear. Sometimes this is left off by careless rebuilders. If this part is missing, your thermostat might get "confused" by the cool draft that it's in. I hadn't thought of this before, but that could be a real problem, because your engine could be hot while the thermostat is still cool.

With that ducting in place the thermostat will open and close with engine temp even in the winter.

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----------------------------------------------- Jim Adney snipped-for-privacy@vwtype3.org Madison, WI 53711 USA

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Reply to
Jim Adney

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Chris Perdue

*All opinions are those of the author of this post* "Sometimes you're the windshield, sometimes you're the bug"
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reply take your PANTS off
Reply to
Chris Perdue

Excellent :)

Jan

Reply to
Jan

Hi.Thank you very much.That is exactly what I was looking for.Steve

Reply to
Ilambert

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