To Flap or Not to Flap

OK – as you all know, in the late 60’s some people got the idea that removing the cooling flaps from the dog house on the air-cooled VW engine made them run cooler. I saw it develop into a mantra from So Cal and other places in the Southwest. It was common for VW shops to remove them or disable them. I’ve seen some engines with the thermostats unscrewed and others with the actuating rods cut. Many, many of them had the flaps completely removed from the doghouse. All for the cause of running cooler.
I’m going to keep it simple here. I’ve owned split window buses. I have owned bugs. I ran dune buggies. I saw them with many different setups for cooling that are seen today; remote coolers, spin on oil filters, and large sump oil reservoirs. None of these did the job, evidenced by the fact the engines, largely, still ran HOT!

Now let’s face it……there are many reasons the VW has the reputation for “running hot”. BUT… when they came from the factory, they didn’t. What was the cause of the change? It’s hard to say, but I can tell you my observations – bear with me, I’m getting to the flaps…

When VW’s were imported in numbers to the United States in the late 1950’s-early 1960’s, there were very few certified/authorized VW service centers in the US. Consequently, many VW’s ended up at non-VW dealerships or service shops for service. The non-conventional air cooled Volkswagens from German factories became mainstreamed in non VW service centers across the country and in the process, the valves were set to many different specs.
I remember the late 60’s, when many shops had one gauge for setting valves…it was referred to as a ‘go-no-go’ gauge. I remember once when a mechanic at the VW dealer on NW 7th avenue in Miami said he adjusted the valves with the engine idling very slowly, till the valves wouldn’t clatter. That’s kind of like today when you try to get your VW brakes adjusted at a muffler shop or other non-VW service center! You know – you may have seen it: the guy stabs at the backing plate adjuster hole with a screw driver until any one of the shoes sucks up and touches the drum. The guy feels drag on the wheel and says you’re good to go. Then your brakes feel lousy because they are stopping with only one shoe per wheel instead of two. This gives the VW Thing a reputation for bad brakes so – here goes – the aftermarket sellers can sell you on disc brake set ups. Same ole same ole marketing.

Anyway, I digress. The flaps are there for a reason. They are restrictive and directional.  First, they are somewhat restrictive, because they SLOW DOWN the cooling air coming from the doghouse fan. This allows the air to absorb more heat from the heads. Second, they are directional. They slant and so direct the air to the hottest areas of the heads under the cylinder head tin. The German engineers knew what they were doing on this for sure. Now don’t get me wrong here – there are other things that will make your engine run hot; timing, carburetor jetting, wrong oil, valves too tight, compression too high for the fuel, restriction in the fan, stuck oil relief plunger, handbrake partially engaged, low oil pressure, low oil, as well as the old favorite, too much carb for the cam.

However, the main thing that is apparent to me is the flaps should be left in place, and operating correctly.  Did you know they are adjustable from the factory as well? Push the thermostat bracket all the way up and it’s set for summer driving… pull it all the way down, and it’s set for winter driving. These are also factory designed to ‘fail in the open position’ if something hits the bracket under the Thing. That’s why they are spring loaded behind the doghouse. With the lousy fuel available these days, especially the ethanol based crap they are selling, I build all my engines to 6.8 to 1 compression ratio. No higher than 7.0 to 1 with good gas. The ethanol raises the octane….but lowers the boiling point of the fuel – a sure-fire formula for vapor lock in warm weather. This makes it more important to run the flaps, as well as reduce the compression ratio.

Here in Idaho where we run in the high desert and enjoy annual summer rallies to the Arizona Strip or many other places in the Western US, at sustained speeds of around 60-65 mph, we use electric fuel pumps in addition to the stock mechanicals. Contact me for those part numbers if you like.