If you don’t have the time, or the skills to remove a fuel tank in order to clean it, here is how to clean a fuel tank without removing it:
1. Read the instruction manual. Before starting, find the instruction manual and see how to disconnect the fuel tank lines. This step is important because fuel tank lines vary on make and model. Make sure you follow the safety instructions.
2. Drain the fuel tank. This is probably the most important step. You need to drain the fuel tank completely. A good way to do this is to leave the car running until it’s the last drop of fuel. You can also jack your car from one side so the fuel can drain better from the tank.
3. De-grease your fuel tank. After you drain your fuel tank, but it still smells of gasoline, you need to de-grease your tank. De-greasing your fuel tank will bring a better result. You can use a commercial de-greaser or mix some dish detergent and hot water. Leave this mixture in the tank for 24 hours. If it still smells after 24 hours, do this step again.
4. Pressure wash your fuel tank. After the degreasing process is done, you need to wash your tank with water. Use a pressure washer to wash out all the debris, dust, and dirt from the tank. Try to point your sprayer at various angles inside the tank so you can remove the rust from the fuel tank walls. Make sure you are wearing goggles as debris may get into your eyes.
5. Adding a cleaning solution. Your fuel tank probably has grime or rust in it. For this, you will need to use a cleaning solution. The chemicals from the cleaning solutions will break down the rust. After applying the cleaning solution, you will be able to wash off the dirt and debris easily. Try using some professional-grade acid solutions.
6. Leave the tank. You need to allow the cleaning solution to sit for a couple of hours. I left my tank for 5 hours total. After that, I was able to remove the rust and sludge very easily. If you don’t have much free time, I think that leaving it for 2 hours will do the job.
7. Rinse the fuel tank. Rinse your tank properly with some water. Spray with water until there is no more smell of gasoline manual. After you are done with cleaning, you need to leave the tank for 24-48 hours to dry. Make sure your fuel tank is dried completely. You do not want to leave water in your fuel tank. Again, after it is dried, make sure there is no smell of gasoline.