Condensed water under tank cap
5 Reasons Why Condensed Water Under the Fuel Tank Cap Is Concerning – and How XADO Can Fix It
Condensed water under the fuel tank cap is a common but often overlooked problem. It occurs when warm, humid air inside the tank cools down and forms water droplets on the internal surfaces. This is especially common when the tank is not full, or when the vehicle is exposed to large temperature changes. Water can also enter the tank during refuelling, particularly in older fuel stations or in wet weather.
Over time, this moisture mixes with fuel and leads to a range of engine and fuel system issues. Diesel engines are especially vulnerable, as water contamination can cause freezing, corrosion, and injector malfunction. Below are the five main reasons why condensed water under the tank cap should never be ignored.
1. Water Causes Corrosion Inside the Fuel Tank
Even small amounts of water can cause corrosion on the internal surfaces of the fuel tank. This corrosion can lead to rust particles entering the fuel system, clogging filters, damaging injectors, and reducing overall engine performance. Modern fuel systems are highly sensitive, and corrosion-related debris can cause expensive repairs.
Keeping the tank at least half full reduces the amount of air — and therefore moisture — inside the tank. Using a moisture‑removing additive such as Aquastop helps eliminate water before corrosion begins.
2. Water Contaminates Fuel and Affects Combustion
When water mixes with fuel, it disrupts the combustion process. This can lead to unstable engine revolutions, jerking during acceleration, and poor fuel efficiency. Diesel engines are particularly sensitive, as water contamination can cause injector misfires and incomplete combustion.
Symptoms often appear when driving on uneven roads or when the tank is nearly empty. Removing moisture from the fuel system helps restore smooth engine operation.
3. Water Can Freeze in Cold Weather
In winter, condensed water can freeze inside the fuel lines, fuel hose, or main filter — especially in diesel engines. Frozen moisture restricts fuel flow, causing the engine to stall or fail to start. This is one of the most common cold‑weather issues for diesel vehicles.
Using a water‑removing additive prevents freezing and protects the fuel system during low temperatures. For more information on fuel system freezing and moisture, see this article from Drive Quip
4. Water Damages Fuel Pumps and Glow Plugs
Water contamination can cause premature wear of the fuel pump, as water reduces lubrication and increases friction inside the pump mechanism. In diesel engines, glow plugs are also at risk — moisture can cause them to malfunction, leading to difficult cold starts and rough idling.
Removing water from the fuel system helps protect these components and extend their lifespan.
5. Water Leads to Poor Engine Performance and Reliability
When water accumulates in the fuel system, the engine may experience hesitation, jerking, unstable idle, and reduced power. These symptoms are often more noticeable when the tank is not full, as water mixes more easily with fuel when the fuel level is low.
Eliminating moisture ensures consistent engine performance and prevents long‑term damage.
Recommended XADO Products for Removing Water from the Fuel System
Condensed water can be successfully eliminated from the tank and fuel system using the following XADO products:
- Aquastop water remover from gasoline
- PETROLTANK complex cleaner of the fuel system
- Advanced RED Petrol Gas Fuel System Cleaner – optimises fuel properties and cleans the engine fuel system
- Atomex MultiCleaner for diesel fuel systems
- Atomex Multi Cleaner for petrol engines
Aquastop – Water Remover from Gasoline
Aquastop is a specialised product designed to eliminate moisture from the fuel system. It restores fuel system components, prevents corrosion, and protects against freezing. The product also defrosts locks and prevents them from freezing in cold weather.
Properties
- Quickly eliminates water from the fuel system
- Protects the fuel tank from moisture
- Prevents corrosion in the fuel system
Application
- Add Aquastop into the fuel tank at a ratio of 10 ml per 5 litres of gasoline
- Drive as usual
Conclusion
Condensed water under the fuel tank cap is more than a minor inconvenience — it can lead to corrosion, freezing, poor engine performance, and costly repairs. XADO products such as Aquastop, PETROLTANK, and Atomex MultiCleaner provide effective solutions to eliminate moisture, protect the fuel system, and restore reliable engine performance.
Explore more solutions in our Fuel System Cleaners Collection.