1998 Chevrolet Express Van Owner's Manual - Page 222

Engine Fan Noise Your vehicle has a clutched engine cooling fan. When the fan air clutch is engaged, the spins faster to provide more to cool the engine. In most everyday driving conditions, the fan is spinning slower and the clutch is not fully engaged. This improves fuel economy and reduces fan noise. Under heavy vehicle loading, trailer towing and/or high outside temperatures, the fan speed increases as the clutch more fully engages. you may hear an increase in So fan noise. This is normal and should not mistaken as be the transmission slipping or making extra shifts. It is merely the cooling system functioning properly. The fan will slow down when additional cooling is not required and the clutch partially disengages. If a Tire Goes Flat It's unusual for a tire to "blow out" while you're driving, especially if you maintainyour tires properly.If air goes out of a tire, it's much more likely to leak out slowly. But if you should ever have a "blowout," here are a few tips about what to expect and what to do: If a front tire fails, the flat tire will create a drag that pulls the vehicle toward that side. Take your foot off the accelerator pedal and grip the steering wheel firmly. Steer tomaintain lane position, and then gently brake to a stop well out of the trafficlane. You may also hear this fan noise when you start the engine. It will go away as the fan clutch partially disengages. A rear blowout, particularly on a curve, acts much like a skid and may require the same correction you'd use in a skid. In any rear blowout, remove your foot fromthe accelerator pedal. Get the vehicle under control by steering the way you want the vehicleto go. It may be very bumpy and noisy, but you can still steer. Gently brake to a stop -- well off the road if possible. next part shows how to use your If a tire goes flat, the jacking equipment to change a flat tire safely.