Aircooled engine cooling

When summer is here that hopefully means that we are experiencing warmer air temperatures. With warmer air temperatures, comes warmer engines. Those using aircooled engines will find it even harder to keep the engine cool during the summer months and we have all seen the odd VW at the side of the motorway! Don’t let that be you (not through overheating anyway!)

The tinware on a 1.6 Type 1 engine

Although it may seem like a small detail, to ensure cooler engine temperatures, it is absolutely vital that the tinware and engine compartment rubber seals are all present and intact. This ensures that there is cool air above the engine and hot air below it. These are known as the cool and warm zones. If tinware parts are missing, or the seals around the front and back of the engine are torn or broken, hot air will be drawn from the cylinder heads and exhaust back into the cool zone around the top of the engine and then sucked in by the cooling fan and re-circulated over the cylinders and heads, causing the engine temperature to rise, potentially to a critical level. This can cause all kinds of problems over time, some of which may not be immediately obvious, from hot starting troubles, to cracked cylinder heads, up to and including a seized engine.

If you’ve just bought a car/bus, it is well worth checking the condition of the tinware and seals and also making sure that there are no foreign bodies stuck in the cooling fan (remember to do this with the engine turned off!)

If you are fitting a reconditioned or new engine, don’t just rely on refitting the parts that were on the old engine, as they may not be correct either.

The thermostat is another vital piece in the cooling system. There is a set of flaps inside the fan shroud, that actually block cooling air when the engine is cold, in order to warm up the engine more quickly. These are opened by the thermostat, located between the cylinder barrels and if this part is defective your engine will very quickly overheat. Check the function of the thermostat and flaps and if required, replace. The alternative is to completely remove the thermostat and flaps, which while it certainly simplifies matters, is not ideal. It means that your engine may never reach the correct operating temperature in cold weather conditions.

The last few points to consider are your ignition timing, air leaks and fueling. Poor ignition timing can cause your engine to run too hot, it’s unlikely to be visible if it’s wrong but you should hear it. Fuel mixture is equally important, so ensure the carburettor jetting is correct for the size of the engine, fuel starvation will raise the
engine temperature internally. Your fuel system could be setup perfectly, but if your engine is sucking air in elsewhere through a split hose or a broken gasket, then the whole fuel/air mixture is compromised and the chances of running lean and therefore hot, are increased too. Spraying the intake system with Wd40 whilst running will help to detect this, an air leak will suck the spray in, using it as fuel and changing the engine note at the same time.

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