Question -
I told you that our car is tin-less at the moment. Also the tubes that run from the fan down to the heater boxes fell apart in my hands when I removed them -- real junk. I need to find some good substantial ones.
Quick question - I need to not drive the car until I get those fresh air tubes replaced, right? Aren't the heater boxes relied on in the design to remove heat regardless of whether that heat is used to warm the cabin?
Rob responded -
If you need to drive the car -- just block off the air outlets on the fan shroud, so it does waste all the cooling air out the heater holes. Just a number of thicknesses of aluminum foil molded over the hole and held with the hose clamp or some twist wire will do the trick until you get new tubes. The holes in the lower tinware where the pipes went through underneath would be best blocked up too, but the car should be OK with them open unless you drive a long distance on a really hot day, when the mixing of old and new cooling air would become a problem.
Rob wrote, regarding the 009/oil cooler mismatch -
Another problem occurs in mismatching the 009 with the doghouse or non doghouse cooler engines. Up to and including 1970, the air cooling shroud had an internal the oil cooler, and this meant that #3 cylinder (left front) got WARM air for it's cooling and therefore ran hotter than the others. So VW altered the timing on #3 only the cam in the vacuum distributors has #3 cut 2-3 degrees later than the other three cylinders, to reduce the heat load on that cylinder a little. The early 009s also had this feature.
But since 71 the engines have a doghouse oil cooler which sticks out the front of the fan shroud, and dumps that air overboard through some extra tinware, and the fan itself is a little larger to supply this extra air. You should be able to see/feel this cooler sticking out the front of your engine front is front of car of the shroud slight left of centre, and when under the car should be able to see the rectangular air outlet in the tinware just above the bell housing. If the shroud is smooth/straight right across the front of the shroud, you have the earlier type of "in shroud" cooler.
So with the newer type oil cooler, #3 cylinder now gets nice cool air for cooling, and the retard on #3 is not needed. The double vacuum distributors therefore have no retard on #3 (double vacuum distributors were only used on 71 up engines). And they dropped the retard on 009s about 10 years ago too. So SOME 009s have the retard, some don't. You need to make sure you have the right one. The only way to tell is to time the engine on #1 as it should be, then look at the timing for #3 (turn the engine 360 degrees). If the points open at the same time OK, but if the points are opening later (the timing mark is now more about 4 5mm to the right) it's the WRONG 009 for a doghouse cooler engine.
You see where messing with VW's design leads -- YOU become the engineer! This is OK so long as you know what you are doing, but most folks operate in a "partial information" arena, and don't realize that the alterations may not be compatible.
Question -
Remember the suggestion of plugging the fresh air snouts in the summer to provide more cooling air to the engine? Do you think this is a good idea or not? Sounds good in theory...
Rob responded -
The heater exchangers are designed so that a proportion of air is constantly flowing through them, even if the heater is turned off you can see the slot shaped outlet at the top/front of the exchangers, above the actuating flap. I think this is designed so that when you DO need the heaters they haven't filled up with smelly old/dust and such. Therefore plugging the shroud outlets in hot weather probably would provide a tiny amount of extra air to the cylinders/heads.
But I don't think it would be very much Bob Hoover described the airflow through the shroud and cylinder/head finning in one of his 'sermons' (he did some comprehensive studies of this many years ago using an electric blower to measure airflow through the tinware), and in essence he said that the shroud provides a "header" or "supply tank" for the air, and the actual flow is controlled by the close fit of the tinware over the cylinders/heads, and the size and spacing of the fins (leaving a certain amount of space for actual airflow).
Bob also commented on the heater outlets in the shroud and the fact that they were "channeled" internally off the shroud not just holes, and that this tended to separate the airflow through the heater pipes from the airflow through the cylinders/heads. I gathered from this that he meant that blocking the outlets completely would not make much difference to the airflow over the cylinders compared to having the heaters fully installed (since those channels were separated internally), but he did note that leaving them open reduced the air pressure inside the shroud which resulted in lowering airflow over the cylinders that is it's the air pressure above the cylinders which is important more so than the quantity of air available from the fan (which is more than sufficient).
This fits with my understanding of the doghouse cooler too. The fan on these cars is fatter for greater airflow, because the cooling air through the cooler is vented overboard BEFORE the cylinders get the air. But if you have a close look at the doghouse shroud internally, it has two distinct separate passages leading from fan to the oil cooler (one from each side of the fan) -- that "separation of airflow" again; so the bigger fan is designed to maintain the shroud air pressure in the rest of the shroud whilst allowing a separate additional flow to the cooler.
The upshot of all this is that the fan has been designed to maintain a certain positive pressure in the shroud (which then acts like a pressure tank on an air compressor for even airflow to the tool), and although there is some relationship between leakage (wasted airflow) from any source, and the cylinder temps, it's the PRESSURE which is more important, and blocking the heater outlets in the shroud will only marginally increase that pressure when compared with the heaters fully installed.
Question -
I discovered that the oil cooler tin on the front (I sure want to say "back"!) of the fan shroud has a corner missing -- seems to have been torn off from the look of the ragged edge, and left a hole about an inch and a half in diameter.
Rob responded -
A good thing to find and fix -- it can only help the bug's cooling for next summer.
Is the damaged piece sort of L shaped? If so, it's the famous "Hoover bit" (after Bob Hoover, who pounds the importance of this piece in maintaining a proper airflow through the doghouse cooler).
Rob's response to a question about a dirty fan -
The bit about the dirty fan caught my attention I know mine's got a layer of crud on it, and I intend to get it sparkly too. I wonder if it will run a little quieter with a clean fan -- I imagine the crud would have to disturb the airflow through the fan somewhat. Probably not enough difference to here though (through the exhaust noise etc).
Question -
I can't imagine why someone tore that L piece off (the "Hoover bit") -- it fits just below the oil cooler and properly directs the air out through the little downspout thru the firewall tin. Otherwise it could get sucked right back into the fan.
Rob responded -
Yes -- without this the engine will run hotter as some of the oil cooling air will get back into the fan just as you said. I don't know why people think they can leave this off -- it's an essential part of the cooling system in doghouse cooler engines.
Bob Hoover gets REALLY annoyed when he sees this part missing -- I guess the car will survive OK in cooler climates, but he lives in LA, and I bet there have been a few cooked engines around there running without that little part.
Question -
Yesterday when I was poking around the engine tin I noticed two horizontal pieces, one on each side, between the push rod tubes and the cylinders. I'm enclosing a scan of the picture ... Can you enlighten me regarding the function of these tin pieces?
Rob responded -
These are essential parts of the cooling system which force the cooling air to pass through the cylinder fins rather than leaking down between the cylinders and doing no cooling. Because they also restrict the air path to just the cylinder fins, they help to maintain the positive pressure in the fan shroud above, which is needed to force the cooling air through the fins. Without the over pressure from the fan, the air moving through the fins get hot, expands, and forms a "plug" between the fins, which slows down the flow, and the engine is undercooled, so it's ESSENTIAL that these are in place.
On Type 3s (and can be retro fitted to beetles), a modification to these is called "cool tins". These are better shaped pieces which are "molded" to the shape of the fins (kind of inverted V shaped) to even more carefully control the airflow between the cylinders. Often fitted to higher capacity VW engines so they get every scrap of cooling they can get.
Regarding the engine lid, Rob commented -
My '68 Bug always smells a little hot after a run, and I keep the speed to 50mph to limit it. That's the solid engine lid I think - Have to get a slotted engine lid for him.
Question -
I want a cool running engine, one that can take 70 mph into a headwind at 95 degrees all day.
Rob responded -
The stock cooling system will handle higher power OK, but DO include the thermostat and cooling flaps.
One useful trick is to examine the heads carefully, and use a dremel or small chisel to remove any casting flash between the fins - this improves airflow for better cooling.
Paint the cylinders (not the heads) with a very thin coat of matt black heat resistant paint (brush-on, not spray paint -- according to John Connolly, using the brush-on type is much better than spray-on, maybe it sticks better. Also paint the push rod tubes with the same stuff (that will cool the oil just a little, since it's just come from the hotter heads and is dribbling past the cooler cylinder air).
It's possible you might need "cool tins" too - these are advanced forms of the small deflector plates used on upright engines - they were developed for the Type 3 engine. They replace the flat deflector plates under/between the cylinders. They control the cylinder air flow much more closely, and increase the air pressure above the cylinders so the heads get better cooling. Probably not needed, but can be fitted later if needed.
If it's really needed you can alter the oil cooler doghouse to fit the wider type4 oil cooler.
Question -
I asked Speedy Jim about these things; he wrote back -
Sorry. My personal feeling is that all of those measures are "lily-gilding". Any improvement is likely to be small and probably insignificant.
Rob responded -
He might be right.
But the "cool tins" I think might help. They cup the underside of the cylinders and have smallish outlet holes for the cylinder air. That means they restrict the cylinder cooling air a little, and that means there's more air forced through the heads. The cool tins also have small sections which cup the underside outer corners of the heads, redirecting the head air right through the underside head fining near the exhaust valves - less "spillage" means better cooling.
Having looked at a lot of aircooled aircraft engines (which have very close cowling and tinware around the cylinders and heads), I can see exactly what VW were trying to do with the "cool tins" and I've thought it would be a good thing to try in my warmer climate.
Here's a picture of this cooling tin from John Connolly's page (Aircooled.Net).
You can see that cupping BOTH sides of the cylinder undersides with an exit hole in the middle will force the cooling air around more finning, in contrast to the flat deflectors which just send it roughly across the bottom of the cylinders, and you can also see the little "wings" (in the center on that picture) which cup the exhaust valve area of the head for better cooling there.
I think the small flat deflectors in the center of the head area ("between" the cylinders sections) still stays in place, but the larger one between the cylinders comes out.
You have to remove the push rod tubes to install the cooling tin, then replace the push rod tubes.
Question -
It was very warm yesterday, and in the ten miles to the paint shop (all highway, 60mph and greater) the Bug got pretty warm. The dipstick wasn't scalding hot, but it was hot. I knelt down and checked out the thermostat and it was fully extended (though it seemed a little crooked). I reached back and wiggled the cooling vane control rod, but I couldn't remember which way is open and which way is closed (and it was pretty warm back there to stay very long!).
Rob responded -
I'd just look at the thermostat - if it's expanded, the flaps should be open OK as long as the control rod is moving freely.
Question -
I'm wondering if I should install a temperature sensor.
Rob responded -
I've often thought of doing this myself, but never got round to it. I like the sump plug sensor idea myself, not because it's more accurate (it will read about the same), but because it's cheaper. Of course you can use a Gene Berg dipstick sensor which connects to the oil pressure wire and causes the oil pressure light to blink when the engine is too hot - no extra gauges needed, but it's only a "hot or not hot" warning - maybe too simple.
Question -
I'm a bit spooked by the wiring for the sump plug temperature sensor -- I assume you would need to run a wire from the sensor up under the back seat, maybe? And then forward to the gauge?
Rob responded -
I think most of them are resistor type sensors, so the wiring is basically 12+ to sensor, sensor to gauge + and then gauge - to ground. If the sensor has two wires I guess one would be grounded. So yes - you'd need at least one wire from the sensor under the car (or in the engine bay) up to the gauge at the front. From under the car you could probably push the wire through the grommet for the heavy starter cable, then run it under the carpet or whatever. I'm not certain of any of this, but I would imagine it would have instructions or pretty pictures etc.
Question -
Gene Berg gives technical information in his manual regarding temperature gauges. I'd be most interested in your comments.
>Why We Don't Sell Gauges - Technical Info - Most Gauges Are "Horrible!"
Rob responded -
I've heard about the Berg dipstick sender, and how it works.
It sounds like a very simple, reasonably foolproof way of checking oil temp, but of course it only tells you when you've reached the limit (the oil light flickers) - not that the problem is developing, like gauges should.
He says that gauges are usually WAY off - I have no idea how inaccurate they are myself, though I've heard plenty of people say, use them as an indication - not as gospel. Oil temp is reasonably easy to check - dip the sender in boiling water and see where the needle lies in relation to 100c (212f). You could check it at say 80c too (comparing with a cooking thermometer) so you got some kind of "scale" of inaccuracy. Cylinder head temperature gauges would be much harder to check, since you are dealing with much higher temps, though you CAN get infrared thermometers you just point at the part to get the real temp off - perfect for checking against a cylinder-head gauge I would think (you could point the infra-red thing at the underside of the cylinder head and cylinders etc.
I don't know WHY gauges should be way off the mark - it should be easy enough for a manufacturer to calibrate them reasonably accurately, and if they are all so far off as Berg suggests - what does that say for factory fitted gauges in modern cars?
Question -
I really would like to do something that will have a measurable effect on the engine operating temperature. I've heard people talk about compression ratio...
Rob responded -
I think you have about the right compression ratio for that fuel (92 octane). If the compression ratio is too low, the valve timing needs changing and the car losses tractability.
Question -
I'm told the only way to reduce the operating temperature of the engine is to reduce the head temperature.
Rob responded -
That's generally true - since it's the hottest part, getting those temps down helps a lot.
Dare I say it - those shiny aluminium rocker covers don't help - the black VW ones shed more oil heat according to Bob Hoover. Apparently VW offered an Arctic Kit many years ago which included chrome rocker covers to slow the radiation of heat in cold climates.
Question -
What about a larger oil sump? The Gene Berg catalog says that oils sumps aren't really effective in reducing the oil temperature.
Rob responded -
True - you only end up with MORE hot oil. The deep sumps don't have enough surface area to make much cooling difference. They were originally designed to prevent oil surge in hard cornering (racing), not for oil temperature reasons.
Question -
I suppose increased air flow would help; do the stand-off engine lid brackets provide increased air flow?
Rob responded -
On cars with solid engines lids - yes. On those with slotted lids - not enough to make it worth the "ugly".
Disclaimer stuff: Rob and Dave have prepared this information from their own experiences. We have not assumed any specialised mechanical knowledge, but we DO assume that anyone using this information has at least some basic mechanical ability.
We hope you find this information useful, but we don't take any responsibility for anything which happens to you, other people, your VW or any other property or goods resulting from your use of this material.
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Last revised 16 May 2004.
