Oil consumption is a topic that most people might not think about. But when you're driving a rig that requires about 11 gallons of engine oil, it's something that can cost you money and time. So we asked Dan Arcy, our resident technical expert, to share his opinions and tackle this topic.
In this article we'll go over some of the basic questions surrounding oil consumption. More specifically, we'll talk about excess oil consumption, a costly problem, so we'll take time to focus on four key questions.
- What is excess oil consumption?
- How can it hurt?
- What causes excess oil consumption?
- How can you fix it?
1. What is excess oil consumption?
In heavy-duty trucks, what defines “excess oil consumption”? How much is too much?
All engine manufacturers have specific warrantable levels of oil consumption - what they expect their engines to go through as part of normal operating conditions. These levels really help define what is excessive in a given engine.
Engine, Age, and Oil Consumption
Oil consumption changes as your engine ages. Typically, a new engine will have a "breaking-in" period which might call for a high consumption of oil.
The increased oil consumption tends to fall off after the engine breaks in. And then as the engine ages – as you get toward the end of the life cycle of the engine – the oil consumption tends to rise again. We'll discuss the mechanical reasons for this in a moment.
Heavy Loads, Extreme Conditions, Increased Demand
There are many other factors that affect oil consumption. If you are pulling heavy loads in the mountains, you are going to consume a lot more oil than if you are pulling a light load on a flat surface.
The harder a diesel engine works, the more oil it will consume. Idle time also must be taken into consideration. If you are sitting there idling, you are going to use more oil than you should.
Does Viscosity Effect Consumption?
Changing the viscosity of your engine oil can also make a difference. For example, if you change from a 15W-40 to a 10W-30, you should see a slight increase in oil consumption because you now have a slightly lighter viscosity oil in your engine.
Do The Right Thing
Similarly, extending drain intervals beyond reasonable limits can also lead to excessive oil consumption.
With this in mind, I would have to say that the simplest definition of excessive consumption is anything that exceeds the engine manufacturer’s recommended guidelines, bearing in mind all of these other factors for conditions.
2. How can it hurt?
Stress, contamination, and the environment
Stresses
When you are consuming an excessive amount of oil, and constantly running a gallon or more lower than you should be, you are putting excessive stress on the oil that is left in the engine.
For example, when you have a situation where nine gallons is having to do the work of ten, the additives in the oil are going to be consumed at a faster rate. You can actually wear out the oil.
Deposits and Lost Performance
Additional problems can occur if you are burning the oil – carbon deposits will form on the valves and in the combustion chamber.
If the oil is getting up into the combustion chamber, it also can cause deposits to form on top of the pistons. Burning also will cause deposits on the exhaust valves. Then you are not going to have the proper airflow through the engine, which will result in a loss of power and overall engine performance.
The Environment
There also are environmental problems that can result. If you are leaking oil, it is going on the ground. This should be a concern for anyone operating a truck. Excessive burning brings about another environmental matter. This could easily create a situation where unsafe particulates from your emissions are coming out of the exhaust.
3. What causes excess oil consumption?
Under normal operating conditions, excess oil consumption is generally a mechanical problem.
Technically Speaking
Oil is consumed in one of two ways:
- You either burn it
- You leak it
Leaking
In the majority of cases where we have investigated oil consumption problems, it usually turns out to be a leak issue – either the valve cover gasket is leaking, or one of the main seals is leaking. Something along those lines. A bad gasket down in the pan could also cause the leaking.
Burning
When you are burning too much oil, it might also be because you're not using a high enough quality oil.
The reason I say this is because if you are using a high quality oil, it is going to keep the piston ring areas clean, and the ring belt areas clean. If those areas are kept clean and free of carbon deposits and such, you will not consume as much oil. But when those get dirty and covered with carbon and the rings can’t move freely. You will start to have a high oil consumption rate.
4. How can you fix it?
How can excess oil consumption be prevented through preventative maintenance?
The first thing I'd recommend is that truck operators always use a premium product (Shell Rotella T has an excellent record of performance in diesel engines). The newer CI-4 oils perform much better than previous oil because your volatility control is better. Also, the detergency and cleanliness additives are much better.
Unfortunately when it comes to mechanical issues like excessively dirty piston ring areas, changing to a quality oil is probably not going to do you any good. That said, your best bet is to use the better quality oils from the outset and then throughout the life of your engine.
