Air Cleaner Thermostat

[cferry7]

Hello -

Can you explain When (Open / Closed) and the Purpose of the Thermostat on the Oil Bath Air Cleaner unit ?

The specification and writing on the Opening of the Pre-heater Hose Flap confused me today, when I was reading Bentley.
1971 Super.
Confused and Tired.


_________________
1st : ' 71 Super , 1641 cc , ~ Stock - a keeper !
2nd: ' 70 Standard , Totaled 7-14-01 , R.I.P.

[Lowenhart72]

The thermostat holds the flap closed when the engine is cold, so only warm air is allowed into the engine so it warms up faster. As the engine heats up (or under sudden acceleration), the thermostat opens the flap, allowing cooler air in to keep the engine at optimal operating temperature, so you get the best power under any driving conditions (and it reduces exhaust gas emissions).

Hopefully I've explained it a little bit better . I read the Bentley summary of it myself and it took me a few times to completely understand what he was saying.
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'72 Super Beetle - "Actaeus"

BLTN

"It is better to light one small candle than to curse the darkness." -Confucius

[VeedubPastor]

I beg to differ. The flaps in the shroud under the control of the thermostat control the operating temp. The flap in the air cleaner along with the heat riser tubes help control carb icing - not engine temp. On some cars, the two are tied together with a cable which might make you think they are related. Actually, on my 71, the flap in the air cleaner flap is completely separate(controlled by a separate wax thermostat) and is controlled by ambient air temp - not engine temp.
_________________
1971 Super Beetle - Daily Driver
Solex H30/31 & 034 distributor (yeah, I know)
Stock thermostat & flaps
Stock air cleaner and emissions equipment

[vw_hank]

[VeedubPastor]

I know which one they were talking about.
_________________
1971 Super Beetle - Daily Driver
Solex H30/31 & 034 distributor (yeah, I know)
Stock thermostat & flaps
Stock air cleaner and emissions equipment

[torsionbar]

[torsionbar]

[Lowenhart72]

I was speaking from the point of view of someone who's car has all of the parts still attached, because mine does (and IMHO, cars that still have them should be left that way) He asked about the air cleaner thermostat, so I did my best to explain it in a way that wouldn't be confusing so I left details out.
_________________
'72 Super Beetle - "Actaeus"

BLTN

"It is better to light one small candle than to curse the darkness." -Confucius

[VeedubPastor]

[Lowenhart72]

I understood you just fine. I didn't need condescension, thank you very much. I will admit that I made a few errors. The earlier air cleaner pre heating valve (installed before December 1972) is sensitive to engine load, the later is not. And I did make it sound like it controls engine temperature. I didn't state that the original purpose of the valve was to prevent carburetor icing.
The Bentley manual says:

"The later valve keeps the flap closed to cool air regardless of engine load during the warm up period. The early valve allows the flap to admit cool air under heavy engine loads."

I merely tried to help someone out, but because it seems to offend so many others, I won't do it anymore.
_________________
'72 Super Beetle - "Actaeus"

BLTN

"It is better to light one small candle than to curse the darkness." -Confucius

[VeedubPastor]

No offense taken and no condescending intended. I was criticizing my own post because I tend to overcomplicate things sometimes and confuse people.
_________________
1971 Super Beetle - Daily Driver
Solex H30/31 & 034 distributor (yeah, I know)
Stock thermostat & flaps
Stock air cleaner and emissions equipment

[Koeppler]

[MagmaJctAz]

I do a lot of automotive related reading, not always specific to VWs. The ultimate intent of regulating intake air temperature has to do with where the fuel is "put into" the engine.

Well vaporized fuel burns much more efficiently than atomized fuel. Vaporized fuel needs to be warm enough to remain in a vapor state. This is the intent of heat risers and preheated intake air.

This is even true in my mother-in-law's `84 Cougar with fuel injection I am responsible for maintaining. See, it has throttle body fuel injection. The air/fuel must travel through the intake manifold. If too cool, the fuel will not remain a vapor, not burning as efficiently.

As emissions requirements became more stringent, carburetors had to be calibrated leaner. This presented problems if the fuel wasn't as completely vaporized as it could be. Lean misfire would be the result. So VW engineers made changes to the heat riser and the intake preheat to "fine tune" fuel vaporization for reduced emissions.

Port fuel injection, which injects fuel immediately above the intake valve, don't need preheated air, nor hear risers. Because the intake valve makes up part of the combustion chamber, it gets plenty hot enough to vaporize the fuel from the injector. There are no provisions for heat risers or intake preheat when port fuel injection is used.
_________________
1974 Super Beetle. Owned since 1995. Daily Driver. Turned over odometer twice!
1971 Fastback. Check out my Fastback resurrection thread!
http://www.thesamba.com/vw/forum/viewtopic.php?t=627711&highlight=

[MagmaJctAz]

I do a lot of automotive related reading, not always specific to VWs. The ultimate intent of regulating intake air temperature has to do with where the fuel is "put into" the engine.

Well vaporized fuel burns much more efficiently than atomized fuel. Vaporized fuel needs to be warm enough to remain in a vapor state. This is the intent of heat risers and preheated intake air.

This is even true in my mother-in-law's `84 Cougar with fuel injection I am responsible for maintaining. See, it has throttle body fuel injection. The air/fuel must travel through the intake manifold. If too cool, the fuel will not remain a vapor, not burning as efficiently.

As emissions requirements became more stringent, carburetors had to be calibrated leaner. This presented problems if the fuel wasn't as completely vaporized as it could be. Lean misfire would be the result. So VW engineers made changes to the heat riser and the intake preheat to "fine tune" fuel vaporization for reduced emissions.

Port fuel injection, which injects fuel immediately above the intake valve, don't need preheated air, nor hear risers. Because the intake valve makes up part of the combustion chamber, it gets plenty hot enough to vaporize the fuel from the injector. There are no provisions for heat risers or intake preheat when port fuel injection is used.
_________________
1974 Super Beetle. Owned since 1995. Daily Driver. Turned over odometer twice!
1971 Fastback. Check out my Fastback resurrection thread!
http://www.thesamba.com/vw/forum/viewtopic.php?t=627711&highlight=

[Joel]

[VeedubPastor]

[Boble]

I had problems with my 72 some time ago. 1300 DP. It has the oil bath type air filter with the thermostatic valve on top. Issue: Hard to get it to idle properly on cold or half-warm engine.

I was spending all my time on adjusting the carb and playing with dwell and timing. No results. I then replaced the flap in the air intake, and *voilâ* - it works perfect.

Lesson learned: The functioning of the vacuum operated flap in the air filter intake is a lot more important than I first thought. It does not only prevent de-icing, it also influences air/fuel mix significantly in the period between when the autochoke is "completed" and the engine is fully warmed up.

Also, it may be an often overlooked source for air leaks. Undelines the fact that absolutely everything must be in good working order and well adjusted for the stock engines to work right.

[VeedubPastor]

[Boble]

To summarize the functions of this important little piece:

The thermostatic vacuum valve used on late models: (Note that the plastic pipe goes to the intake manifold or carb. The brass tube towards the vacuum operated flap in the air filter intake.)

Low temperature inside the air filter: The thermostatic valve is open, the flap is lifted up by the vacuum, and the carb gets pre-heated air:

Higher temperature inside the air filter: The thermostatic valve closes, the flap goes down to closed position, and the carb gets ambient (cold) air:

This function prevents carburetor icing, and also ensures that the air/fuel mixture is more correct. Typical failures are defect valve (engine always gets cold air), and defect air flap that don't lift to upwards position (engine always gets cold air + potential air leaks)

The mechanism is similar on the paper type air filters, although the flap is positioned a little differently.

[emu88]

Need a diagram like above for the 1971 air filter without the two vaccuum ports on the top. I cant understand if i need one flap and weight for it or two.
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03/1971, 1302 Super Beetle 1600 dual port
Solex 34-pict 3
SVDA Bosch distributor
Long reach heads