Overheating due to wrong serpentine/drive belt routing

The serpentine belt is a very important part of the engine, for those engines that use it. Remember that cars like the Toyota hybrid Synergy Drives do not use serpentine belt, rather many accessories are powered electrically, directly from battery and inverter/converter sources.

The serpentine belt is one part of the engine that does more than one function.

Functions of the serpentine belt

It is used to drive various accessories of the engine through the crankshaft pulley. Accessories that the belt drives are:

1. Water pump
2. Alternator
3. Power steering
4. AC compressor
And so on.....

Engine overheat is a condition where the temperature of the engine rises above the normal operating temperature.

Engines have specific ways which their belts are routed from the crankshaft pulley through rollers and belt tensioners to the various engine accessories.

It is very important to get the routing correctly as an error would cause a wrong direction of rotation of the accessories.

How wrong serpentine belt routing causes wrong coolant pump rotation and overheating

This will be explained with a practical example of a volkswagen passat 3.6L VR6 engine overheat.The customer contacted us on phone and explained the overheating problem of the car claiming that everything some other technicianstried didn't resolve the issue but coolant kept bubbling out from the expansion tank.
We explained to him that we are suspecting an issue around the water pump after he sent a video showing the coolant bubbling out of the water pump but another technician gave him a hundred percent assurance that it is an engine top gasket fault.
To cut the long story short, the engine top gasket was replaced but the fault condition remained.
At this point, the owner had no choice but to bring the car to us and upon visual inspection, we immediately realised that wrong belt routing was turning the coolant pump in the opposite direction of the correct rotation.

In fact, a smaller belt compared to the stock belt was installed in the car.

We got another belt, placed it correctly and viola! Coolant bubbling and overheating problem was solved.

This kind of fault resolution might look simple but can chew a complete day of work or more, even from an experienced technician if proper care is not taken. Hence, attention is to be given to the belt size and belt routing pattern specified by the engine manufacturer.