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On 14 Jun 2001, at 20:02, David Britton wrote: > Jim Adney Wrote: > > >One thing to ask is how they feel about the aircooled thermostat > >assembly. If they tell you that they always take it out, or disable it, > > >find another shop. > > What's the downside of removing or disabling the thermostat assy? > I know of 2 people that have their engines that way. They say it's no > big deal here in CA. Sometimes I suspect these parts are left out because the mechanic is not sure of how to properly reassemble and adjust them. Sometimes this is done on purpose. This approach to cooling is based on the assumption that cooler is better. This assumption is false. All engines are designed, by necessity, to operate at some temperature above "room" temp. The clearances between internal engine parts were chosen so that once the engine was at its proper operating temp the clearances would be optimum to minimize wear and maximize efficiency. Think of things like aluminum (which has a high coefficient of thermal expansion) pistons riding in steel (which has a low coefficient of thermal expansion) cylinders. Did you know that cylinders are round but that pistons are NOT round? Pistons are shaped slightly oval when cold so that they will be round when hot. This is necessary because the pistons do not run at a completely even temp, due to the differences in the structures on their underside. The people who design ALL engines, not just VW, design them to run at a particular temp. Too hot is certainly hard on them, but too cool is also. Did you know that in a typical city 30 minute drive something like 50% of the wear occurs during the first 5 minutes of warmup? If you omit the thermostat in order to "help" your engine run cooler, you are prolonging the warmup time and generally increasing the wear. Gene Berg has a good paper available on cooling and the down side of removing the thermostat system. While most of his tests were done on beetles, I believe most of what he observed applys to us also. He found that in addition to prolonging the warmup time, removing the cooling control vanes also caused SOME part of the engine to run HOTTER than before. While it's true that the CA weather is often warmer than mine, you have to remember that our thermostats are set to try to regulate the exhaust cooling air to ~155F. That's awfully hot for any of us. When you start up your car on a 50 deg day it wants to get to 155 as fast as possible. The cars that VW supplied to Africa and the Sahara were still supplied with the thermostats. Another problem for FI type 3s is that if the temp sensor on #4 cylinder never warms up the FI will always run rich. This pumps extra gas into the cylinders, some of which washes the oil off the cylinder walls instead of burning. Extra piston ring and cylinder wear is the result. This problem acually happens to all engines right after startup, but can be worse on FI engines if they are never allowed to reach operating temp. For a more complete explanation, read this book by Bill Fisher. It debunks this and a number of other VW myths and tells you what really DOES work, as opposed to what makes money for the retailers. Certainly it was written a long time ago, but it's still the best book I know of for this kind of information. How to Hotrod Volkswagen Engines by Bill Fisher published by H. P. Books, Tucson, AZ, 1970 ISBN 0-912656-03-4 (excellent book, well written and researched) - Jim Adney jadney@vwtype3.org Madison, WI 53711-3054 USA ------------------------------------------------------------------- Search old messages on the Web! Visit http://www.vwtype3.org/list/