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From the Archives: Vehicle Lightweight

Archive Issue Nov/Dec 2017: Cooling Corner, By: Steve Schaeber

Tight Threads

As vehicle manufacturers continue working towards higher fuel economy vehicles, one of the easiest things they can do is to lightweight the vehicle. This means rethinking the function, shape, design and materials used in almost every part. This ensures they can weigh as little as possible, at the right cost, and will perform the same function as before the process.

In some cases, this means turning to plastics. Many composites can yield parts as strong or even stronger than their metallic counterparts. Of course, the added benefit of plastic is that it generally weighs much less than most metals do. Less weight means less mass for the engine to move around. This in turn uses less fuel and can really add up over time.

Lightweight Material Affects

One common cooling system component that has long been made of plastic is the overflow bottle (or surge tank, depending on the application). For these, plastic is an ideal material. It is able to be molded into seemingly limitless shapes. This can then be mounted on firewalls, above wheel wells, atop engines, or even integrated into fan shrouds or other sub-assemblies.

One thing you may have noticed is that some tanks, depending on their design and application, also incorporate metal necks. In some cases, they even incorporate plastic threads, to secure their pressure caps. For most installations, these connections give little or no problems. However, in some cases, it’s found that the plastic threads can become warped or disfigured over time. This makes it quite difficult to remove or install the cap. Generally, this is caused by thermocycling, a wide or rapid changes in temperature over time. This can repeatedly expand and contract the material.

Recommendations for lightweight

A similar situation was noticed by Jaguar, which is documented in technical service bulletin # JTB00518NAS2. They describe how an engine coolant leak may be found coming from the engine coolant expansion tank filler neck. This might also include steam coming from under the hood. It can even include an engine overheating warning message being displayed on the instrument cluster.

This specific condition could be caused by a distorted engine coolant expansion tank filler neck, which can be checked for out-of-round and compared to factory specs. Jaguar recommends using a Vernier caliper to measure the diameter of the tank’s filler neck in at least two places. After making the first measurement and jotting down the diameter, rotate the tool 90° and take a second reading. Then, compare the two measurements. If the dimensions across the centerline of the neck are less than 50.70mm, a new engine coolant expansion tank must be installed, along with a new coolant pressure cap. If the dimensions are more than 50.70mm however, then the sealing bead should be visually inspected for damage. Including things like a cut, chip or gouge that could be allowing coolant and vapors to escape from the tank. If the sealing bead is damaged, a new tank should be installed.

However, if the dimensions are correct and no damage is found, then a new pressure cap may fix the leak.

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