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Pepperbilly
Samba Member
Joined: April 08, 2017
Posts: 977
Location: Seattle, Wa
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 Posted: Sat Sep 02, 2023 10:21 am Post subject: Intake cold air Duct |
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Because my Goldie is a wagon I have never worked on sedans or coupes. But now that I have I wonder about the importance on the coupes, sedans of the connecting duct between the hood and fan housing. I have seen some missing.
Is this duct for the benefit of the attached blower for the heating system to draw in cool, clean air only or does it also benefit and aid the engine cooling? I guess this confuses me a bit. Buses with type 4 engines are just open to the cooling fan with no ducting. Why the difference in design?
Bill |
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raygreenwood
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Joined: November 24, 2008
Posts: 21521
Location: Oklahoma City
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| Posted: Sat Sep 02, 2023 6:43 pm Post subject: Re: Intake cold air Duct |
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| Pepperbilly wrote: |
Because my Goldie is a wagon I have never worked on sedans or coupes. But now that I have I wonder about the importance on the coupes, sedans of the connecting duct between the hood and fan housing. I have seen some missing.
Is this duct for the benefit of the attached blower for the heating system to draw in cool, clean air only or does it also benefit and aid the engine cooling? I guess this confuses me a bit. Buses with type 4 engines are just open to the cooling fan with no ducting. Why the difference in design?
Bill |
Which duct are we speaking of? The large oval one between the cooling shroud and the chassis in the very back? Or the smaller one in the engine compartment in some wagons and sedans?
Or are you speaking of the duct under the dash that connect to the fan?
Ray |
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Pepperbilly
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Joined: April 08, 2017
Posts: 977
Location: Seattle, Wa
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| Posted: Sat Sep 02, 2023 10:05 pm Post subject: Re: Intake cold air Duct |
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The large light colored fiberglass type piece that is bolted to the frame lip and seals to the deck lid when you close it at the engine compartment. Also has the heater system electrical assist blower fan mounted on it. This is not on a wagon.
Bill |
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Lars S
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Joined: October 04, 2007
Posts: 786
Location: Sweden
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| Posted: Sun Sep 03, 2023 9:16 am Post subject: Re: Intake cold air Duct |
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Good point Bill! I have also wondered about this.
The engine fan is ducted to ambient air on (what I remember) all other aircooled VWs than the buses. (Well the beetle has not the fan ducted but the air is separated from the exhaust heat thanks to the thight engine tin).
Besides getting cooler air for the engine this arrangement also brings fresher ( less smokey) air to the heating system.
The heavy loaded buses takes its cooling air from directely above the muffler - how do they survive that? (Maybe the answer is: they dont!?)
Lars S
_________________
Porsche 914 -72, Bahia Red daily driver 
VW411 2-d -70, White, sold 
VW412 4-d, -73, Gold Metallic, daily driver
Suzuki T500, -69, Candy Gold, sold
Suzuki K50, -77, Black, daily driver
BMW R69S -69, White, sold
Husqvarna 118cc, -47, Black, Sold |
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raygreenwood
Samba Member
Joined: November 24, 2008
Posts: 21521
Location: Oklahoma City
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| Posted: Sun Sep 03, 2023 10:22 am Post subject: Re: Intake cold air Duct |
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| Pepperbilly wrote: |
The large light colored fiberglass type piece that is bolted to the frame lip and seals to the deck lid when you close it at the engine compartment. Also has the heater system electrical assist blower fan mounted on it. This is not on a wagon.
Bill |
Ah....I misread your post.  I thought you were working on a wagon.
So the large "nylon" scoop/duct with the leaf screen and gasket that is one sedans!
How important it is.....is directly proportional to how well your engine compartment is sealed.
Problems that can be caused without this duct in place:
1. You can get a fair amount of water spraying around in the engine compartment when driving in moderate to heavy rain. At various times I have driven without it while working on items and this has happened.
However, it's not clear whether it's driving at high speeds or low speeds in rain that allows water past the deck lid duct.
2. If your engine bay is not sealed.....you are pulling in hot exhaust for engine intake and heater.
And when your engine bay is sealed, in hot weather you are pulling in some pretty hot air for engine.....and I will say probably only at low speeds in traffic....stop and go.
So years back, someone on the STF was running a 411 or 412 sedan with a sealed engine compartment and without the big scoop.....using a bus type leaf screen over the engine fan intake and said they had no problems.
They made the point that as long as you keep stuff out of the fan with the screen and make sure items like coils and relays are covered or maybe slightly moved to deal with rain and have a good gasket around the deck lid.....you still have just as much cold fresh air entering the engine compartment.....and it keeps the whole engine bay....cooler.
That is a problem in hot climates in a 411/412 sedan. The engine bay being totally sealed off....does get raging hot in the summer. I think this causes a few problems with lifespan of some plastic parts and other items in the summertime under the hood.......so whomever posted that.....it was making some sense.
I took note of that conversation because....there are several parts that if you screw them up...they are damn hard to replace (the rubber accordion boot, the plastic connecter that feeds into the fan, the rubber intake elbow for the air cleaner).....and without those parts....it's hard to make the big scoop work well anyway.
Lars, part of the conversation that I spoke of above also referenced the bay buses with type 4 engines.
The bay buses use the same lower sheet metal seal to keep heat from exhaust and exhaust gases out that the 411/412 use.
But, remember that the buses have those big louvered scoops one on each side that just dump cooling air into the engine compartment on each side. So essentially, running a bus is pretty much similar to running a a 411/412 without its dedicated scoop.
It does keep the top components of the engine much cooler in buses than we do in 411,/412.
Is it possible the buses run hotter because of this set up?
I don't think so. The cooling air in the bus comes from way up high, far away from exhaust. They do run some risk in the fall of getting the leaf screen over the fan plugged up with leaves. But the main reason the bus runs hot is its heavy, geared low, low compression and had horrible aerodynamics.
So, if you had to run without the scoop....I think you could with no problems. Ray |
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Pepperbilly
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Joined: April 08, 2017
Posts: 977
Location: Seattle, Wa
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| Posted: Sun Sep 03, 2023 12:15 pm Post subject: Re: Intake cold air Duct |
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Hey Guys,
This is an interesting subject! We can speak about theory here and speak about real world outcomes…
Lars, you brought up a good point about the bus type 4 arrangement where the fan takes all it’s cooling air in above the muffler. That would also be true with the 411/412. That is why both these models have the insulated heat shields above the muffler. So important to keep the temps down in that location. With the upright engines the fan is in a different location so no need for a heat shield above the muffler.
Ray, getting back to the big oval sedan duct. The manner in which the auxiliary heater blower fan is dealt with is different between 411/412 and Buses. This part is interesting. In the sedans the heater blower is attached to the oval duct and is then drawing in clean, cool fresh air. The buses heater blower motor is just hanging out in the open with no ducting, consequently drawing in both engine compartment stale dirty air and cleaner scooped air combined. That is a big difference I don’t quite understand. I am no engineer though. Sooo, then I have to believe that the 411/412 wagons have the best designed cooling ducting. The wagon has a dedicated ducting channel in the body directly linked to the fender intake louvers. On the left side of the car the heater blower fan is directly attached to the body duct drawing in only nice clean cool air. Anyway, I am thinking that the sedan oval duct is very important to the heating system and may be the largest reason for this duct. Is that what the engineers were thinking?
Bill |
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Lars S
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Joined: October 04, 2007
Posts: 786
Location: Sweden
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| Posted: Sun Sep 03, 2023 9:14 pm Post subject: Re: Intake cold air Duct |
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| raygreenwood wrote: |
.....
Lars, part of the conversation that I spoke of above also referenced the bay buses with type 4 engines.
The bay buses use the same lower sheet metal seal to keep heat from exhaust and exhaust gases out that the 411/412 use.
...Ray |
You are correct Ray, the buses also have a lower sheet metal over the exhaust / under the fan...the bus engine bay I was looking at was missing that part and misled me....
Lars S
_________________
Porsche 914 -72, Bahia Red daily driver
VW411 2-d -70, White, sold
VW412 4-d, -73, Gold Metallic, daily driver
Suzuki T500, -69, Candy Gold, sold
Suzuki K50, -77, Black, daily driver
BMW R69S -69, White, sold
Husqvarna 118cc, -47, Black, Sold |
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raygreenwood
Samba Member
Joined: November 24, 2008
Posts: 21521
Location: Oklahoma City
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| Posted: Mon Sep 04, 2023 7:29 am Post subject: Re: Intake cold air Duct |
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| Pepperbilly wrote: |
Hey Guys,
This is an interesting subject! We can speak about theory here and speak about real world outcomes…
Lars, you brought up a good point about the bus type 4 arrangement where the fan takes all it’s cooling air in above the muffler. That would also be true with the 411/412. That is why both these models have the insulated heat shields above the muffler. So important to keep the temps down in that location. With the upright engines the fan is in a different location so no need for a heat shield above the muffler.
Ray, getting back to the big oval sedan duct. The manner in which the auxiliary heater blower fan is dealt with is different between 411/412 and Buses. This part is interesting. In the sedans the heater blower is attached to the oval duct and is then drawing in clean, cool fresh air. The buses heater blower motor is just hanging out in the open with no ducting, consequently drawing in both engine compartment stale dirty air and cleaner scooped air combined. That is a big difference I don’t quite understand. I am no engineer though. Sooo, then I have to believe that the 411/412 wagons have the best designed cooling ducting. The wagon has a dedicated ducting channel in the body directly linked to the fender intake louvers. On the left side of the car the heater blower fan is directly attached to the body duct drawing in only nice clean cool air. Anyway, I am thinking that the sedan oval duct is very important to the heating system and may be the largest reason for this duct. Is that what the engineers were thinking?
Bill |
The thing is that as far as sheet metal and sealing out heat from the exhaust and road dust from below.....the bus is no different than 411 and 412. Same engine compartment seal part #for all three.
So, with the two large scoops on the bus there really is no "stale" air as there CIS a lot of air ripping through the engine compartment from the two upper scoops.
In threads a while back when I brought up the issue of hot components inside or a fully sealed engine compartment needing to be made of the right materials and 0last8cs to survive.....the bus guys reminded me of their two big upper scoops....and pointed out that their engine bay is only sealed at the bottom and does not get very hot....compared to a 411 or 412.
I think a couple of people posted they measured upper engine component temps of between 125° and 150° max.
My point of view was from fully sealed 411 and 412 engine compartments. I have measured distributor temps in the summer on a highway drive at 250°+.
As far as dust and exhaust.....all of that comes from down low. I can see why our type 4's "might"need a dedicated fresh air duct for the heater fan.
I think they did what they did with the bay window bus heater fan...because the fresh qir intakes are high enough up that they are "getting away" with it.....except that I have read comments from a few owners over the years that if they have lots of leaking oil...they get oil smells, or if they are running rich or burning oil and sit in traffic they can pull some of that in.
I would bet that if a sedan owner was going to run without an intake scoop, they could probably fashion a simple upturn elbow to take advantage of the intake air be8jg clean and still coming in through the hood. Ray |
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Pepperbilly
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Joined: April 08, 2017
Posts: 977
Location: Seattle, Wa
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| Posted: Mon Sep 04, 2023 9:20 pm Post subject: Re: Intake cold air Duct |
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So it looks like you better run with that oval air intake in place on 411/412's. The intake either fuel injected or carbureted has always been connected to cool outside air flow on both sedans and wagons. Even type 3's were set up like that. As Ray pointed out, the buses apparently have an abundance of scooped outside fresh air. This allows the engine compartment to stay cooler and no need to plumb the carbs or injection for outside fresh air. The people at VW designed these things in for a good reason.
Bill |
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raygreenwood
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Joined: November 24, 2008
Posts: 21521
Location: Oklahoma City
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| Posted: Tue Sep 05, 2023 9:34 am Post subject: Re: Intake cold air Duct |
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| Pepperbilly wrote: |
So it looks like you better run with that oval air intake in place on 411/412's. The intake either fuel injected or carbureted has always been connected to cool outside air flow on both sedans and wagons. Even type 3's were set up like that. As Ray pointed out, the buses apparently have an abundance of scooped outside fresh air. This allows the engine compartment to stay cooler and no need to plumb the carbs or injection for outside fresh air. The people at VW designed these things in for a good reason.
Bill |
Kind of true.....but with the type 3 there is no sheet metal bulkhead or engine compartment lower seal to prevent dust and exhaust heat from being sucked into the cooling system. You can see all the way to the pavement when you look in a type 3 engine bay.....so the type 3 100% NEEDS the boot/duct going to the intake louvers on the sides of the car.
Kind of what I was getting at is that with a 411/412 sedan.....as long as you have the sheet metal engine surround and the foam seal to keep out road dust and exhaust heat.....even without the scoop you still have all of that cool air coming through the oval hole in the engine lid.
As I noted, someone here in the forums ran this way....no scoop....with only a bus style leaf screen over the fan intake and had no reported problems.
You will not get any less air through the louvers in the hatch. But whether that let's too much water to spray around in the engine bay during rain driving....I just don't know. The hatch has drains in the rear edge and is kind of an "S" baffle inside.
Also I just don't know if having general high volume air entering the engine bay but not being concentrated at the fan will create intake issues. I don't think so....as the bus and 914 survive without dedicated duct to fan.
Just some thoughts. Ray |
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Pepperbilly
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Joined: April 08, 2017
Posts: 977
Location: Seattle, Wa
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| Posted: Tue Sep 05, 2023 11:43 am Post subject: Re: Intake cold air Duct |
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Yes Ray that all makes sense.
This is a little off the track but we have been discussing it. I have heard from you and someone else now that engine compartment temps can get pretty high on the wagons and sedans. Looks like high enough to start melting ignition parts! Melting the distributor rotor and other such parts. I am wondering what was wrong under these conditions… guess it could be many things? All I know is my Goldie has been built to factory standards, including using the original style domed pistons. All the tin is correct, the thermostat is in place and working, all boots and seals in place. Using the original ignition distributor which works like it should. I do run a partial synthetic Brad Penn 20W50 oil. I don’t have any oil/cyl head temp gauges to monitor but I burn no oil or have any unusual signs of overheating. It runs as if factory new.
Bill |
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raygreenwood
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Joined: November 24, 2008
Posts: 21521
Location: Oklahoma City
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| Posted: Tue Sep 05, 2023 12:57 pm Post subject: Re: Intake cold air Duct |
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| Pepperbilly wrote: |
Yes Ray that all makes sense.
This is a little off the track but we have been discussing it. I have heard from you and someone else now that engine compartment temps can get pretty high on the wagons and sedans. Looks like high enough to start melting ignition parts! Melting the distributor rotor and other such parts. I am wondering what was wrong under these conditions… guess it could be many things? All I know is my Goldie has been built to factory standards, including using the original style domed pistons. All the tin is correct, the thermostat is in place and working, all boots and seals in place. Using the original ignition distributor which works like it should. I do run a partial synthetic Brad Penn 20W50 oil. I don’t have any oil/cyl head temp gauges to monitor but I burn no oil or have any unusual signs of overheating. It runs as if factory new.
Bill |
So....parts that will melt due to heat (melt is a strong word)....lets call it "distort"...inside the engine bay are:
1. On rare occasions I have heard and seen pictures of the epoxy in teh groove on a rotor kind of getting gooey. Thats not out of the question for epoxy.
2. Nylon parts and polypropylene. Examples can be the scoop itself, later models that used the plastic round air cleaner....that air cleaner can warp (been there and done that), and some of the plastic hose ducting, the plastic ring and plug on the alternator and a few other parts.
What causes this...in my experience....is a combination of things creating a REALLY hot engine.
Not running all of the sheet metal and the foam seal and sitting in stop and go traffic will inject a huge amount of heat especially on the rearward side of the engine.
Metal parts near this like the sheet metal, the coil and its clamp and the distributor and cooling housing in this situation can get hot enough to burn you. Easily 250 F.
Add in 100 degree weather....mixed highway driving and stop and go traffic in these same conditions and you can find the distributor hot 250 to 300 F. Been there....done that.
The distributor on 411 and 412 gets hotter than distributors in types 1, 2, and 3 because if the case is overly hot its pulling heat out of that and has virtually no airflow around it in the sealed engine compartment...and it has its own internal heat source with 10-20Kv electrical arcs flying around every 90*.
If you add in more external heat from no foam seal or sheet metal....which will cause the engine to run hotter anyway....you get more heat across the board and the distributor has very little surface area to shed this.
If you are using poor grease in the distributor its common to find that the distributor temps in hot weather on a 411 or 412....cause the grease to run/flow...making greasy points and causing issues.
The nylon parts under the hood are all Nylon 6. This nylon grade has a hard "melt" point...meaning it loses shape and flows....of about 420 F.
But, it starts to deform or warp....if its under any kind of load like clamped or connected to a hose etc....at about 320* F.
I suggest a test if you want to play around.
Order like a 20 foot spool of thermocouple wire. Should be maybe $1 per foot at most. You really do not need to solder it, for this test you can twist it very tightly together at the measuring/hot end.
Get a flat pin plug on line (maybe $5 from the same source.). Connect it all up so it plugs into your voltmeter so you can read temperature while you drive in the cockpit.
Test #1:
Tape the TC to the inside of the lower most plastic duct about 2" from the fan with duct tape with the twisted toegether end sicking out in the air. Drive this around for about 10 minutes to get a baseline temp with the factory set up.
Pull over and remove the big duct. I have this down to about 1-2 minutes....two phillips screws up top, two wires at the fan, the clamp for the intake boot to the air cleaner and pull the accordion loose at the bottom and the whole pile comes out.
Drive it around and see if the intake temperature in front of the fan gets higher.
Test #2: If you are driving around for an hour or so, tape the TC to the side of the distributor with all of the ducting in place and drive around and get a baseline for distributor temperature.
Then remove the duct and repeat.
Ray |
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Wildthings
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Joined: March 13, 2005
Posts: 50360
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| Posted: Tue Oct 03, 2023 10:18 pm Post subject: Re: Intake cold air Duct |
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Its been a long time, but from memory the Type 4 cars really fried their oil when SD and SF oils were what was available, just as bad if not worse than a bus did. I acquired this 1974 1800 engine from a 412 almost 20 years ago and have good reason to believe it had been off the road for 10+ years at that time.
It is a a baked mess with wear that just isn't seen all that much with today's oils. It had 0.015" of taper to the cylinders, whereas the high mileage rebuilt 1800 in my bus (also originally from a 412) had zero taper at 250K miles.
My personal belief is that the cooling duct may make things worse and not better. It would be interesting to do Ray's intake air temperature tests. The ignition coil and distributor get quite hot on a Type 4 car with the duct in place when compared to a bus. The "meat" thermometer you can get from Harbor Freight for 10ish bucks and then extend to the front with some doorbell wire would be a cheap way to do the test. |
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