Katerina Swanson
Mixing diesel fuel and hydraulic fluid is not recommended as it can cause issues with the pump and cylinder seals. However, some people intentionally mix diesel and hydraulic oil to improve turning forces in hydraulic steering systems. If diesel is accidentally added to a hydraulic tank, it is generally recommended to drain and refill the tank with new hydraulic oil, as diesel can thin the hydraulic oil and cause issues, especially on long runs or hot days.
Characteristics and Values
| Characteristics | Values |
|---|---|
| Mixing diesel and hydraulic oil | Not recommended due to potential issues with pump and cylinder seals, and contamination. |
| Impact on viscosity | Diesel can thin hydraulic oil, affecting performance in high-temperature or extended use cases. |
| Impact on seals | Diesel may weaken or damage rubber seals in pumps, hoses, valves, etc. |
| Corrective Action | Drain and replace hydraulic oil. Adding gear oil can counteract thinning. |
| Safety | Diesel is more flammable than hydraulic fluid. |
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What You'll Learn
Diesel in hydraulic tanks is a common issue
If diesel is added to a hydraulic tank, the best course of action is to drain the hydraulic tank completely and refill it with new hydraulic oil. This is because diesel fuel has a lower viscosity than hydraulic oil, so the mixture will be thinner and may not provide adequate lubrication for the hydraulic system. Running a hydraulic system with diesel fuel can lead to problems with pump and cylinder seals, and contaminated hydraulic fluid is a common issue in the marine industry.
However, if the machine has not been started after the diesel was added, simply draining and refilling the tank may be sufficient, as the fluids likely have not mixed. In addition, some older machines used a mix of 50% diesel and 50% oil for flushing hydraulic systems, so a small amount of diesel in the hydraulic tank may not cause significant harm.
In some cases, it may not be possible to completely drain and replace the hydraulic fluid. In these situations, adding gear oil to the hydraulic tank can help counteract the thinning effect of the diesel fuel. For example, adding two quarts of 90-weight gear oil can make the hydraulic fluid thicker again.
It is important to note that while a small amount of diesel in the hydraulic oil may not cause immediate issues, it is still recommended to replace the hydraulic fluid as soon as possible to maintain the proper functioning of the system and prevent potential damage.
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Diesel in hydraulics can cause pump and cylinder seal issues
The addition of diesel fuel can reduce the viscosity of hydraulic fluid, which may be desirable in some steering systems. However, if the diesel content exceeds a few percent, it can lead to issues with the pump and cylinder seals. Diesel has some lubricating properties, but it is not as effective as hydraulic fluid, and the dilution of hydraulic fluid with diesel can result in reduced lubrication and increased wear on pump and cylinder seals.
Furthermore, diesel in the hydraulics can lead to negative pressure in the hydraulic cylinder, causing air to be drawn past the rod seals. This can result in aeration, where air mixes with the hydraulic oil, creating an explosive mixture that can damage the cylinder and burn its seals. This phenomenon is known as the "dieseling effect" and can be caused by various factors, including faulty float valves, worn rod seals, and loose hoses or connections.
To prevent these issues, it is important to ensure proper maintenance and servicing of hydraulic systems, including regular inspection and replacement of seals as needed. It is also crucial to avoid mixing diesel and hydraulic fluid in multi-use containers and to follow the manufacturer's recommendations for the specific hydraulic system.
While some sources suggest that a small amount of diesel in the hydraulic fluid may not cause significant damage, it is always best to consult with experts and follow recommended practices to ensure the optimal performance and longevity of hydraulic systems.
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Flushing the system with diesel was once common
Flushing the system with diesel was once a common practice. In the past, it was not unusual for a manufacturer to suggest a mix of 50/50 oil/diesel for flushing a hydraulic system. This mixture was used to reduce viscosity and improve turning forces in hydraulic steering systems. However, newer fuels may not be as compatible with seals, and both hydraulics and fuel systems have become more chemically different and less tolerant.
While a small amount of diesel in the hydraulic oil or vice versa may not cause significant damage, it is essential to exercise caution with newer equipment. Mixing different fluids in multi-use containers can be risky, and it is always better to check with the manufacturer for specific requirements for hydraulic fluid.
If diesel is accidentally added to the hydraulic tank, the best course of action is to drain the tank and refill it with new hydraulic oil. In some cases, flushing the system with screened used hydraulic oil may be a more cost-effective solution. It is also recommended to properly identify the fill ports to prevent future mix-ups.
Additionally, diesel in the hydraulics can cause problems with pump and cylinder seals, leading to seal failure and contaminated hydraulic fluid. The diesel can soften the rubber seals in pumps, hoses, valves, and rams, resulting in potential leaks and further complications. Therefore, it is crucial to address the issue promptly and ensure a thorough flush of the system.
While flushing the system with diesel was once a common practice, it is no longer recommended due to the potential risks associated with modern equipment and the availability of alternative solutions, such as using screened used hydraulic oil for flushing.
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Diluting hydraulic oil with diesel improves turning forces
Diesel fuel in hydraulic tanks or reservoirs can cause problems. In such cases, it is recommended to drain the hydraulic oil and replace it with a new one. However, some people on forums have mentioned that diluting hydraulic oil with diesel can improve turning forces in hydraulic steering systems.
Tony Athens, a diesel expert, has suggested that diluting hydraulic oil with diesel can improve turning forces in hydraulic steering systems. He recommends a ratio of about 3 parts hydraulic fluid to 1 part diesel. This dilution is said to reduce the viscosity of the hydraulic fluid, making it thinner and easier to turn.
However, it is important to note that mixing different fluids in multi-use containers can be risky. Some people have reported problems with their pump and cylinder seals after accidentally mixing diesel with hydraulic oil. It is always recommended to check with the manufacturer of the equipment before proceeding with any advice from online forums.
Additionally, the type of "O" rings and seals in the hydraulic system can also play a role in determining the compatibility of diesel fuel and hydraulic oil. In some cases, diesel fuel may not cause significant damage to the system, especially if it is a small amount.
While some people have reported successful dilution of hydraulic oil with diesel, it is always a good idea to proceed with caution. It is important to consider the specific requirements of the hydraulic system and seek advice from experts or manufacturers before making any changes.
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Diesel in the tank but not run through the machine is less of a concern
Diesel in the hydraulic tank but not run through the machine is less of a concern. If diesel is poured into a hydraulic tank reservoir, but the machine has not been started, the best course of action is to drain the hydraulic tank and refill it with new oil. This is because diesel fuel can cause issues with the pump and cylinder seals, leading to seal failure and contaminated hydraulic fluid.
In some cases, it may not be possible to completely drain the hydraulic tank and replace all the oil. In such situations, it is recommended to add gear oil to counteract the diesel fuel. The diesel fuel will make the hydraulic oil thinner, and the gear oil will thicken it. The contaminated oil can then be drained and saved to run in the fuel tank, mixing it in a 50/50 ratio so it is not wasted.
It is important to distinguish between diesel in the hydraulic tank and hydraulic fluid in the diesel tank. While a small amount of diesel in the hydraulic oil or vice versa may not cause significant issues, diesel in the hydraulics can be problematic. This is because diesel can affect the pump and cylinder seals, leading to potential seal failure.
To prevent future mishaps, proper labelling and identification of the fill ports for hydraulic oil and diesel fuel are crucial. Additionally, ensuring that the hydraulic tank is easily accessible can help avoid accidental mixing.
In summary, while diesel in the hydraulic tank but not yet run through the machine may cause initial concern, it can be addressed by draining and refilling the tank or adding gear oil to counteract the diesel. However, it is always advisable to exercise caution and consult with equipment mechanics or professionals for specific advice regarding your machinery.
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Frequently asked questions
If you haven't started the machine, you can simply drain the tank and refill it with new hydraulic oil. However, if the machine has been running, you may need to flush the system or replace the seals.
Mixing diesel fuel and hydraulic fluid can cause the hydraulic oil to become thinner. This may affect the performance of your machine, especially after a long run or on a hot day. It is recommended to change the oil and filter to avoid potential issues.
While some sources suggest that diesel fuel can be used to flush hydraulic systems, it is not recommended as a substitute for hydraulic fluid. Diesel fuel may not be compatible with newer seals and can cause softening and damage.
