Fuel tank caps, also known as ‘gas caps’, are an important part of the fuel tank that keeps gas in the vehicle. Despite them being a small feature, they are a fundamental part of allowing vehicles to run properly and in preventing dangerous situations. In this blog post, we will cover the different types of fuel tank caps available and the signs to look out for that mean you may need a replacement, so you can be sure your HGV fuel tank cap is fit for road use.

What do they do?

Fuel tank caps are essential for keeping gas inside the vehicle’s tank. They keep debris and dirt from entering the fuel tank and they act as an extra line of defence, after the fuel tank door, in preventing leakage or contamination. They can also be integral to the vehicle’s fuel efficiency, as gas vapours could leave the tank and go into the atmosphere, not only losing valuable gas for your truck, but also damaging the environment and air quality.

Why is it especially important for HGVs to have them?

HGVs are vulnerable to tipping when cornering or when the vehicle rolls over if the fuel tank isn’t kept upright and it can easily spill if there is no cap. The frequent amount of travelling and long-haul journeys may not be exclusive to HGVs, but they do carry larger fuel tanks, and can carry up to 600 litres of fuel which could result in a large-scale leak. This is why it is fundamental that your truck’s fuel tank cap is sealed and secure, lowering the risk of hazard. The different types that are suitable for each truck may vary, and convenience can also play a factor in choosing a cap.

Types of fuel tank caps

Fuel tank caps, although small, have varying features which serve different purposes. The main types are vented or unvented caps, which can both be suitable for bayonet-style gas tanks. Additional features include those that are lockable with a key, or screw-type caps, both of which can come with a chain (with a chain clip at the end) for extra security.

• Vented caps, also named ‘cap-less’, are the newest invention of the fuel tank cap and are seen in newer vehicles. They are designed to ventilate very small amounts of air into the tank so that the process of combustion can happen, allowing the car to move, as well as preventing a vacuum from forming inside the tank which can lead to the vehicle stalling. It works similarly to a trap door by allowing gas and air inside it whilst keeping dirt and debris out of it. When gas is being put into the filler neck, the pressure from the fuel pump nozzle activates the one-way release valve so that it can start filling the tank up with fuel. Vented caps keep the fuel pressure more consistent which is great at regulating the fuel conditions that allow the vehicle to function in all types of driving conditions reliably. High pressure in the fuel tank can lead to vehicle misfiring and increases vehicle emissions, meaning more fuel is used so money is wasted, as well as affecting the atmosphere. Low pressure is just as bad, and it can cause poor vehicle performance and slow or even no starts. Both of these can reduce fuel efficiency and, in worst cases, shorten the life of an engine. The vented cap offers better chances at maintaining a sustainable engine system.

• Unvented caps are an older invention which were in vehicles until the 1960’s. They are technically still ventilated as they have a tiny hole on the top of the cap but were inefficient at keeping the fuel in the tank as it still splashed out when the vehicle accelerated or turned a corner. We still stock these caps for older vintage trucks and vehicles.

• Caps with keys can offer more security which is great for when unvented caps can easily be removed, and people can steal fuel from your tank. These are usually replacement caps and aren’t already installed in a vehicle, so only you would own the keys to the cap. The downside is that keys can easily be lost and will require a mechanic or a locksmith to open the cap, meaning more money spent.

• Screw-type caps are usually locked into place when rotated clockwise. Common user error has meant that screw-type caps may not be closed tightly enough, so fuel leakage occurs. To avoid this, some other caps have tighter seals so that just a 1/8 turn can ensure the tank is sealed and locked tightly.

The risks

As we have already learnt, HGVs can be susceptible to a great loss of fuel during a leakage which can be expensive. The more dangerous risk with leakage, though, is that large-scale leaks from trucks have the potential to disrupt other road users and can lead to road closures, as an emergency clean-up would have to be executed as soon as possible. Fuel leakages of this size can quickly ignite, causing a fuel fire which can take a long time to put out and can sometimes be fatal. The main cause of heavy-vehicle fires is from a leakage of hot gases which can result from a failure with the fuel tank cap.

 

Signs you need a new fuel cap

To avoid the chances of leaking, replacement caps are the best option if you experience any of the following:

• If your cap doesn’t tighten completely, and you don’t hear a ‘click’. This is a risk as the seal needs to be airtight as dirt can get in. It may be a fault in the seal, or the rubber seal is missing or coming off.
• It is important that the cap is locked tight and hasn’t exceeded the mileage limit (50,000 miles) so that you know it’s not working overtime. We recommend visiting our site for good quality cap replacements that will ensure a safe, leak-free journey.
• You smell a strong fuel smell exuding from the vehicle (with the fuel cap and door closed). This could mean your vehicle is already leaking fuel from the filler neck. It should be replaced straight away.

Drive confidently knowing your fuel tank cap is secure. Truckspares 365 has a range of caps suitable to fit universal or branded trucks. Save on money and get yours at the best price in the market!