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Hello- > "In small engine repair it states 1/3 heat is > conducted through cylinder walls, 1/3 for power > in the cylinder, 1/3 escapes in exhaust." Well, that's certainly not a rule, but it does well to give a very rough first-order approximation to what is happening. The truth is actually much more involved. Believe it or not, the same physics that applies to a watercooled Chevy also applies to an aircooled VW or a Briggs - they are more similar than you think. Blasphemy, I know, but absolutely true. I hesitate to go into more theoretical detail here, because it would take me an hour or two to make a post that most would probably ignore and, of those that read it, only a couple people would even care to understand what I'm saying. The rest would simply argue with me and tell me that physics is wrong. I'm being cynical here, I know, but it's happened to me far too many other times to ignore :-). I will, however, respond to some other things that were said: > In order for oil to cool the engine the heat it absorbs needs to be released. > It is part of the cooling system i.e. it directly cools the engine. I would > venture to say if an oil cooler was simply to keep the oil from breaking down > then those of us with bigger engines (producing more heat) wouldn't be running > with extra oil coolers ;-) Well, that's incorrect. Oil is a _secondary_ coolant in just about all engines. The primary coolant is _always_ the one that is around the cylinders and heads. For a watercooled engine, this is water (or antifreeze or whatever). For an aircooled engine, it's air. The amount of heat released here is MUCH, MUCH more than goes into the oil. Whoever says that aircooled engines are actually oilcooled is false. Until the VW engine grows waterjackets and we fill the waterjackets with oil, it is aircooled :-). The main thing that heats up oil is generally bearing friction. Sustained high RPM and high load make it get hotter. So, bigger engines get bigger oil coolers. If you have a turbo, then it just makes it worse, as often turbos are oilcooled. Cylinder head temperature is a good way to keep tabs on how the primary cooling system is working. Unfortunately, many people don't understand how to make it work better, and so they let their high performance engines overheat. Reduced engine life and/or cracked heats are a common result. > nope, exactly right. the heat path is some from friction, more from > the oil that washes the cylinder walls and rocker areas, but mostly > due to convection to the case from the heads/cylinders. Absolutely false. > i'd like to hear from those running extra oil coolers and see how > often they change valves or replace pistons. i'm guessing they do it > a bit more frequently than normal (flame suit on!) despite the > cooler. They have no _direct_ relation to one another. However, indirectly by personality only, they do have a relation. The majority of people that have "high performance" VW's have added big oil coolers, but have done little to nothing about their primary cooling system. Therefore, the pistons and valves don't like to live long. Those that have tackled the problem properly don't have a problem. The first and most important step is to ditch the cast iron cylinders. I'm not trying to be a salesman here for LN Engineering's products, but for over fifty years, Porsche has ditched cast iron cylinders on their high performance engines. There's a very major reason why. > For us, we have to remember that the middle 1/3 is really all the heat lost > thru the cylinder walls, the head, and the piston, so a lot of this makes its > way outside via the oil. False. The overwhelming majority goes out the cooling fins. For a little rock-solid proof of this, here's a test: get cylinder head temp and oil temp gauges. Then, hit the road for a cruise and note what you see. Then, go back home and disconnect the oil cooler entirely. Repeat the test. Then, reconnect the oil cooler, but kill the engine cooling fan. You won't be able to drive but a few blocks - the head temp will SKYROCKET! I've done a lot of testing without oil coolers at all to prove a point. I do not recommend it in the long run, but it was interesting to see how it actually effected things, verifying the laws of physics I already knew. I've never purposefully done testing without an engine cooling fan. The very few times I accidently did it (belt snapped on a T1), the results were very, very bad. Take care, Shad Laws LN Engineering - Aircooled Precision Performance http://www.lnengineering.com ------------------------------------------------------------------- List info at http://www.vwtype3.org/list | mailto:gregm@vwtype3.org