Why Running Diesel Return Line Into Supply Lines Is A Problem?

Diesel fuel return lines, also known as filter drains, are used to provide an outlet for the return of excess fuel from the primary supply line back to the fuel tank or reservoir.

It’s important to maintain proper flow through these lines to keep the fuel system functioning properly and prevent damage in your vehicle’s power train components.

You can achieve this by using the correct fittings and by avoiding situations that may cause kinks or obstructions in the line. But what about running diesel return line into supply lines? Well, let’s see-

Reasons For Running Diesel Return Line Into Supply Lines

There are 2 common reasons you might want to run your return line into your supply line.

In both cases, running your return line into your supply line avoids potential storage problems down the road. But while these seem like good reasons at first glance, they’re actually more like short-term solutions that can cause long-term headaches.

For one thing, running your lines together means you won’t know how much fuel you have left until it’s too late.

If you get busy with other things and forget to check regularly, before long, your tank will be empty without any warning.

This can lead to having vehicles stranded without fuel or, even worse, damaged due to being left out in bad weather with no power steering or brakes.

Advantages of Having Separate Lines

There are a few reasons why you might want your return line (diesel-out) separate from your supply line (fuel-in).

  1. Safety: If you have an emergency shutdown, you can quickly kill your supply line while leaving your return line open, preventing fuel from spilling out of your tank into your bilge.
  2. Consistency: Having separate lines ensures that each time you fill up with diesel, it goes directly into your tank without mixing with any old fuel in your lines or tank.
  3. Flexibility: If you need to move, you can just disconnect your supply line, fill up with diesel, then reconnect your supply line at your new location.
  4. Portability: If you’re traveling in an area where there are no diesel pumps, you can just fill up your tank by connecting your return line directly to a nearby gas pump (the same way as you would with your supply line).
  5. Fuel Quality: If you’re filling up at a high-quality fuel dock, you can use your return line to drain any bad fuel out of tank before it enters your vehicle systems.

Problems With Mixing a Diesel Return Line Into the Supply Line

There are two major problems with running your diesel return line into your supply line.

This can cause oil starvation issues within your engine. If you take too long to notice an issue, it could lead to serious damage and even death in extreme cases.

You may not be able to avoid mixing these lines completely; however, if you do mix them together, be sure to cut off or reduce your return line so that it isn’t connected to your main supply line while using the generator.

Instead, connect it only once you have started up your vehicle. Doing so will keep you safe and protect your environment from unnecessary pollution.

2 Options For Fixing This Issue

Fixing this issue can be as simple as fixing your leaky supply line. Still, it may also involve changing out your fuel system. Depending on how badly you need an uninterrupted fuel flow, here are two options for dealing with a diesel return line running into your supply line.

Option 1: Switching Out Your Fuel System

If your tank has two different fill points (one for diesel and one for gasoline), switching them could fix the problem right away. However, if you don’t have two separate fill points, then you’ll need to add one.

This can be done by installing an in-tank fuel filter or adding a remote filler neck. These are relatively simple fixes that should only take about an hour of work.

  • This will probably be your easiest option because it requires no extra equipment. All you have to do is switch your current filter with an in-tank fuel filter, which will prevent any liquid from getting into your supply line. At most auto parts stores, you can find one for about $15-$20.
  • You can install a remote filler neck if you don’t want to buy a new in-tank fuel filter or if your vehicle doesn’t have one. These are available at most auto parts stores for about $50-$60 and can be installed by anyone with basic hand tools like wrenches and screwdrivers.

The only downside is that you’ll need to fill up more often than before. But that might not be such a bad thing. For example, installing a remote filler neck could allow you to fill up on diesel when there aren’t many gas stations around.

Option 2: Fixing Your Leaky Supply Line

Sometimes, there’s nothing wrong with your return line-it just happens to be running through a leaky supply line. If you suspect that’s what might be happening, all you have to do is find where your supply line is leaking and fix it.

This could involve replacing a gasket or tightening some clamps, but it shouldn’t take more than an hour of work. And remember, if you don’t know how to fix it yourself, you can always pay someone else to do it for you.

Just make sure they use high-quality parts so you don’t end up dealing with another leak in a few months.

Frequently Asked Questions (FAQs)

Does The Fuel Return Line Have Pressure?

Fuel return lines operate under almost zero pressure. They don’t put any extra force on your engine, but they carry fuel vapor used in your combustion process. If you run both supply and return lines into one tank, then you’re losing all that fuel vapor because of higher pressure pushing it back toward your pump.

How Much Pressure Is In A Diesel Return Line?

The fuel return line typically runs from the tank through an underground pipe or above-ground hose to your in-line fuel filter. This is where gravity takes over and allows excess fuel, water vapor, sediment, and particulates to flow back into your fuel tank. As far as pressure goes, all you need is about two psi (pounds per square inch) of force to push that liquid back into your tank.

How Much Pressure Is On A Diesel Fuel Line?

The fuel pressure inside your diesel fuel lines is typically between 4-6 bar or 55-75 psi.

Last Words

For average off-road enthusiasts, for whom fuel economy is often not an issue, having only one return line might not pose any major problems.

If you’re planning on running diesel return line into supply line or running diesel fuel at higher pressures (above 100 psi), or if you have plans of running waste oil in a multi-tank system, however, you’ll want to avoid returning your excess supply back into your tank.

Doing so can cause pressure issues within your system that may eventually lead to expensive problems down the road.

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Ronald Berit

Our chief editor, working 24/7 to ensure the precise and only quality data regarding different trucks.He is mastered with the ins and outs of cargo to off-road trucks of Dodge, Ford, Chevy, Toyota, GMC and more. This truck geek graduatedwitha Bachelor of automobile engineeringdegree and practiced through his own automotive parts repair center.

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