Heat Exchanger Flaps

[Conners68]

Sorry if this has been asked elsewhere, but I could not find it.
I have pulled down my 1972 1300 Beetle as it needs a major overhaul. The flap that controls the heat inside one of the heat exchanger has come adrift from the control arm and is just rattling about inside.

Is this something that can be repaired? It looks like I might be able to prise some of the cover off, but other parts look welded.

Any advice for a novice mechanic greatly received.

[bikelash]

The heat exchanger can be taken apart but it is a bit of work to do and a bit to put back together. You may have better success searching for one in the classifieds or at a junkyard. (Highly recommend staying with original equipment). There is a post on here that talks about taking one apart and he had to weld it back together IIRC.
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[Conners68]

Thanks Bikelash,
I will have a look around

[Floating VW]

You shouldn't need to split the whole thing just to get at the flap. The top section that holds the flap in place comes off separately, and it's really not that hard to put back on.

Unless you really mangle it during the removal process, you won't need a welder or anything to put it back on, just a stout pair of pliers and maybe a pry-bar or a screwdriver.

Here's what it looks like with the top off:

This is just to show off how proud I am of how my heat exchangers turned out:

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[Volks Wagen]

[Floating VW]

Thanks. You know, I'm not sure if they're OEM or not. They're not OG, with the really nice, deeeeeeeeeeep fins, but they're also not the cheap ones that are basically just a J-pipe in a clam shell. I think they were made in Denmark. One thing is for sure, I spent way more time on them than any normal, well-adjusted human being should.

Here's what the guts look like:

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"It's time you started treating people as individuals, rather than mathematically predictable members of an aggregate set, regardless of how well that works."

[bikelash]

Nicely done! I knew there was a couple of people that had split them open but couldn't track it down in the time I was on earlier.
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64 baja sold
72 sb wrecked
69 baja sold
69 std sold
72 sb sold
54 std sold
74 sb-ongoing
88 westy-ongoing

[Eric&Barb]

Just tripped over this thread. Hate to say it after you put in so much hard work, but those are cheaply built HEs. If you want good heat to the interior and much better engine cooling in the Summer get an OG set and fix them up.

http://www.thesamba.com/vw/forum/viewtopic.php?t=470019&highlight=dansk+cross+section
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[Floating VW]

Yes, for sure this style heat exchanger is less efficient than the deep finned OG style, but I don't believe they're anywhere near as bad as the REALLY cheap ones that don't have any fins at all!

The reason I didn't want to run a set of OG exchangers is because my heating system has been modified and doesn't count on the constant airflow from the fan shroud anymore. I posted of few pics of the system here (I come in towards the middle of page one):

http://www.thesamba.com/vw/forum/viewtopic.php?t=644536&postdays=0&postorder=asc&start=0

Without the constant airflow from the fan shroud, I fully expect the cast aluminum fins to melt soon (if they haven't already), at which point I intend to split the shells open again and weld in some fins of my own design. Doing this to a pair of OG heat exchangers would have been a crime, in my opinion.
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"It's time you started treating people as individuals, rather than mathematically predictable members of an aggregate set, regardless of how well that works."

[Eric&Barb]

Just keep in mind that head and oil temps will run a lot hotter without air flow thru the HEs, and the warmer the weather the more too hot those will get.
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[Floating VW]

[Eric&Barb]

Would guess you were running too hot as is in those conditions. What oil temps were you getting on that run?

Our test is finding ones oil temp runs 30 degrees higher without flow thru the HEs, and once flow was resumed the oil temp dropped back down. Only way the engine oil could be affected by the HEs not having flow is thru the heads. BTDT, and was quite surprised in 70s F weather around town and on the highway.

That thin gasket is not going to do much to insulate from hundreds of degrees of temp. If it did the home housing industry would use that material to insulate homes floors walls and roofs to keep less than a hundred degrees temp from transfering.

Personally think it is more than just one single factor heating up the HEs. The big one possibly being that insulating the HEs with dead air around the exhaust piping is causing the exhaust to not condense as much and in turn causes back pressure and the heads/cylinders run hotter.

As mentioned thru that link Steve of Wolfgang noticed a cooling problem with just going to 60 mm outlet HEs with the inside pipes being corrugated to the earlier 50 mm HEs that just have a round shaped inside pipes. More surface area the more the exhaust heat transfers to the outer fins.
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[Floating VW]

[Eric&Barb]

[Floating VW]

Yes, it would be interesting. My bet is that there would be no change whatsoever, with a slight possibility that cooling down half of the manifolds in my exhaust system would actually make it run a bit worse. I would even go so far as to say that, if you or anyone else thinks they can load up a bug with themselves, plus another 400 pounds worth of tools and spare parts, and make a 3800-foot climb over 36 miles in 116°F heat at 60 mph in top gear AND keep their oil temps below 240°F (using just the stock doghouse oil cooler, heat exchangers are optional), then I am hereby issuing a formal challenge!

I agree that keeping oil temps at or below 220°F could be beneficial to engine longevity. I also believe that a few minutes in the 230-250°F range, such as when operating under a heavy load in extreme ambient temps, will cause no damage to either the oil, or the engine. It is actually very difficult for me to get my oil temps above 220°F. I pretty much have to cruise at 70 mph for 30 minutes, with ambient temps around 95°F, and maybe climb a few hills to do it. And even then, the oil only gets up to around 225°F. Again, this is with no airflow through the heat exchangers.

Could you be more specific about your test? For example, what exactly was blocked and unblocked, and how? Were the tests conducted under similar conditions, i.e. same velocity and load, same ambient temps, etc.? Were the results repeatable, or was it just a single, random event? Can you explain why you got these results?

What I'm trying to get at is that my understanding of how the system works, which is based on data from my own research, tests and observations, has shown me results that appear contradictory to yours. Before I can come to a definitive conclusion as to who I believe is right and who I believe is wrong (if anyone), I need to know why that is.

So, if I understood you correctly, you are saying that, according to your tests, the constant airflow over the no. 1 and no. 3 exhaust manifolds cools the exhaust gases flowing through them, thereby increasing back pressure, and this back pressure then keeps the cylinder heads cool enough to cause a drop in oil temperature of up to 30°F. Is this correct?

I would be leery of oil temperatures below 180°F. I don't know the minimum temperature at which motor oil properly lubricates engine components, but I do know that too cold is just as bad, if not worse, than too hot. 180°F to 230°F is my personal comfort zone. Also, I'm pretty sure the temperature at which the thermostat opens has very little to do with how an ACVW engine maintains proper oil temps.
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[Eric&Barb]

[Floating VW]

OK, so I have a couple of doubts about your test results. You say you blocked off the inlets to the heat exchangers when you did your test. This is good. However, you also say you blocked off the outlets from the fan shroud. This is a very common mistake people make, usually in an attempt to "increase the air going to the heads". The fan shroud "needs" to have a certain amount of air flowing through these outlets to function properly. Along with preventing the cast aluminum fins from melting, I believe this is the real reason why the heat exchangers were designed to allow air to continue to flow through them, even if that air wasn't being used to heat the cabin. Will blocking off those outlets cause a 30°F spike in oil temps? Possibly, but it sounds like a stretch to me.

So, what else could have contributed to such a drastic rise in temperature? I'm wondering if maybe you didn't do your initial test during the heat of the day, perhaps going up the hill on your way to town. And then, a little later in the evening, after unblocking the fan shroud and reconnecting the heat exchangers, you headed for home going down the hill, and noticed that the oil was 30°F cooler. I'm not saying you DID do that, but you can see how these little things could skew your results. The only way to know for sure would be to repeat your test (the more times you repeat it, the better), under the EXACT same conditions as possible. This is why I say I have no doubt that a lack of airflow over my heat exchangers does not cause my engine to run hotter (excepting, of course, the heat exchangers). I have four separate thermometers to monitor both engine and ambient temps (well, technically, one of them is a pyrometer). And, due to the modifications I made to my heating system, I am able to turn on (or off) the air flowing through the heat exchangers with the flick of a switch. Every time I drive the car, these temperatures are observed and compared, and the conditions under which they occured are noted (including when the heat is turned off and on), and this is how I know that everything is functioning well and within normal parameters, every time I drive the car.

The final doubt I have is in regards to your theory of why an "uncooled" exhaust manifold would cause a rise in cylinder head and oil temps. I think we both agree that, for reasons previously stated, heat transfer through conduction, convection and radiation are not likely causes. We also agree that excessive back pressure in the manifold definitely could be a cause. I think the problem with your theory is this:

[Eric&Barb]

[75Flamebug]

How the heck do you get those apart? I try to get my heat exhangers apart, but it was a pain the butt, so I quit on them....
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[Eric&Barb]

There are a few spot welds at the rear you just break loose. Then peel the two sheet metal pieces apart like a banana...
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