Knowing when to change lubricating oil is not always as simple as counting miles or hours. One key factor many people overlook is TCN (Total Contaminant Number). As oil works inside an engine, it slowly collects dirt, soot, metal particles, and other impurities. At Fubex Lubricants, we offer high-quality lubricants for all types of engines. Enjoy fast shipping, a price match guarantee, and no-questions-asked returns. Need help choosing the right oil? Call us at +971 50 544 9614 — our friendly team is ready to assist! Â
If TCN levels get too high, the oil can no longer protect the engine properly. Understanding acceptable TCN limits helps you decide the right time to change oil, prevent engine damage, and keep equipment running smoothly and efficiently.
What is TBN and How Is It Used?
TBN stands for Total Base Number. It shows how well an engine oil can fight acids that build up during engine use. These acids come from fuel burning and can damage engine parts. A higher TBN means the oil can neutralize more acid and protect the engine for a longer time.
To measure TBN, the industry commonly uses the ASTM D2896 test. This test gives an accurate TBN value and helps compare used oil with fresh oil.
Many experts follow the 50% TBN rule. This means the oil should be changed when its TBN drops to half of its original value. For example, if new oil starts with a TBN of 6 mg KOH/g, it should be replaced when it reaches 3 mg KOH/g.
When TBN drops below 50%, the oil can no longer neutralize acids properly. This can cause:
- Oil to become thicker
- Faster oxidation
- Quick breakdown of the lubricant
Most Original Equipment Manufacturers (OEMs) use the 50% TBN rule. These limits are important because engine warranties and service agreements depend on them. They also decide how long oil can safely stay in the engine, which affects how people judge oil quality.
Why Should You Change Your Engine Oil Regularly?
Your car cannot run without engine oil. Engine oil helps the engine parts move smoothly, keeps them clean, and protects them from rust. It also helps control engine heat.
But over time, engine oil gets old and dirty. That’s why changing your engine oil regularly is an important part of car care.
The main job of engine oil is to reduce friction between moving parts inside the engine. Less friction means less damage. As oil moves through the engine, it collects dirt, metal particles, soot, and fuel leftovers. It also has special additives that protect the engine from corrosion and oxidation.
Over time, these additives wear out, and the oil fills up with dirt. When this happens, the oil cannot lubricate properly. This causes more friction, which can reduce engine performance and lower fuel efficiency.
Old and dirty oil can also form sludge, a thick, sticky substance that settles at the bottom of the engine. Sludge blocks oil flow, which can lead to poor engine protection and even engine overheating.
In recent years, oil change intervals have become longer in many countries. This puts extra stress on engine oil and can lead to:
- Oil breaking down due to heat and pressure
- Thicker oil and higher acidity
- More dirt buildup, including soot, metal particles, dust, and water
Changing your engine oil on time helps your engine run smoothly, use less fuel, and produce fewer emissions. Regular oil changes also help extend engine life and save money in the long run.
Challenging Common Beliefs About Stationary Gas Engine Oils
Does Oil Really Need to Be Changed at 50% TBN?
The 50% TBN rule is one of the most trusted rules in the oil industry. For many older stationary gas engine oils, this rule works well. But to make better and longer-lasting oils, we need to understand this rule more clearly.
What Is TBN and How Is It Used?
TBN (Total Base Number) shows how well an oil can neutralize acids inside an engine. Acids form during engine operation and can damage parts. A higher TBN means the oil can fight acids better and protect the engine longer.
The most common test used to measure TBN is ASTM D2896. This test gives a clear TBN value and allows comparison between new oil and used oil.
The 50% TBN rule means oil should be changed when its TBN drops to half of the fresh oil value. For example, if new oil has a TBN of 6, it should be changed when it reaches 3.
Below 50%, the oil cannot neutralize acids properly. This can cause:
- Oil to become thicker
- Faster oxidation
- Quick breakdown of the lubricant
Also Read: What Is the Significance of TBN (Total Base Number) In Engine Oil?
Why Is the 50% TBN Rule Important?
Many Original Equipment Manufacturers (OEMs) follow the 50% TBN rule. These limits are important because engine warranties and service contracts depend on them.
This rule also decides how long oil stays in the engine, which affects how people judge oil quality.
Why Should We Rethink the 50% TBN Rule?
To understand this, we need to look at how the ASTM D2896 test works. In this test, oil is mixed with a very strong acid to measure all the base materials inside the oil.
This method works well for older gas engine oils because their TBN mainly comes from strong base additives that neutralize acids.
However, modern clean-technology gas engine oils are more advanced. They contain both strong and weak base additives, not just one type.
Some weak base additives include:
- Certain antioxidants
- Metal deactivators
Because the test counts all base materials, it may not always show how much real acid-fighting power is left in modern oils. This is why the industry is starting to question whether the 50% TBN rule is always the best guide.
Final Takeaways
Keeping an eye on TCN levels helps you make smarter oil change decisions. As contaminants build up, oil slowly loses its ability to protect engine parts. Changing oil before TCN goes beyond safe limits reduces wear, improves efficiency, and helps prevent costly breakdowns.
Regular oil testing and timely oil changes ensure longer engine life, lower maintenance costs, and reliable performance. By understanding TCN, you can move away from guesswork and give your engine the care it truly needs.
FAQs
Q1: How often should I change synthetic oil?
Synthetic oil usually lasts 7,500–10,000 miles in normal driving. If you drive in heavy traffic, extreme weather, or tow loads, change it sooner—around 5,000–7,500 miles. Always follow your car maker’s advice, especially during warranty.
Q2: What’s the difference between full synthetic and synthetic blend oil intervals?
Full synthetic oil lasts longer—about 10,000–15,000 miles, while synthetic blend oil lasts 5,000–7,500 miles. Full synthetic costs more but needs fewer oil changes and gives better engine protection.
Q3: Can I trust my car’s oil life monitor with synthetic oil?
Yes, oil life monitors track driving conditions, not just miles. They usually match synthetic oil change needs, but you should reset the monitor after every oil change and follow it for warranty safety.
Editor-at-Large
A passionate writer in the lubricant industry, Awais Iqbal has been covering oils, greases, and industrial fluids since the start of his career. At 25, he’s already written for blogs, catalogs, and brand guides across the UAE. Awais’s insights help companies connect with their audience, and his clear, helpful writing style is trusted by brands in the region.
