By Steve Schaeber, MACS Technical Editor
Most modern engines use some type of water pump to circulate antifreeze through the engine and heat exchangers to regulate operating temperature. Many of the engine-driven pumps contain shaft seals that are lubricated by the coolant itself. As part of the pump’s normal operation, these seals are in direct contact with the coolant, which leaks (extremely) slowly past the seal as it provides lubrication. Once past the seal this small amount of fluid collects in an area known as the weep chamber. It’s a place where this leaked coolant has a chance to evaporate, its vapor escaping through a vent or weep hole.
Older style water pumps had a similar setup, although they were designed to simply allow the lubricating coolant to drip past the water pump seal and into the weep hole and drip out of the pump housing, along the front of the engine and eventually down onto the ground, that is if it could make it that far. In most cases, especially when the vehicle is in motion or the engine cooling fan is operating, that dripping coolant would be blown across the front of the engine and evaporate relatively quickly not causing alarm, although over time a rusty stain may develop. As the water pump shaft seal wears out further, the coolant leak rate can increase to the point where it becomes a visible drip or puddle requiring replacement of the pump.
To help technicians diagnose their newest style of water pumps, Ford has issued GSB (General Service Bulletin) # GSB-0000083, “Cooling System – Coolant Pump Warranty Information.” This bulletin, which is intended to explain coolant pump design characteristics and features, what normal staining looks like and show an example of a leak, along with a diagnostic tip. It’s all in an effort to explain what water pump weeping is and how to figure out when to replace the pump.
Newer model Ford engines, such as the 2.0-Litre 4 cylinder in the 2012 Focus, use a type of water pump with a coolant-lubricating seal and integral weep chamber. Any coolant that collects in the chamber later evaporates with normal usage. Sometimes this can result in an exterior stain due to the vapor escaping past the vent hole and collecting on the pump housing rather than on the inside of the weep chamber. Ford wants technicians to know that this is a normal characteristic of the pump style and is not an indication of failure. But if there is wet coolant or puddles on the weep chamber, a quick test can determine whether or not the pump needs to be replaced.
Dry the coolant pump housing using a clean paper towel. You might have to wipe the area a few times, especially if there’s dirt, oil or grime. Allow some time then wipe it again. If the towel only has a dry or waxy residue, the seal is working properly. But if the towel is wet, the pump is leaking and needs to be replaced.
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