Hot Topic: Can You Add Oil to a Hot Engine? Dos and Don’ts

The internal-combustion engine was one of the most important advancements in mobility, as it allowed for covering very large distances on one small tank of fuel. And although it is very complex, it only requires two liquids to run: gas and oil. Sure, most modern engines also need a coolant, but an internal-combustion engine can also be air-cooled.

Both gas and oil are not negotiable – without gas, the engine won't have anything to combust, and without oil, its constituting parts will overheat and wear out in a matter of minutes. Even if there the oil level in your engine is not optimal, it can also result in parts being under-lubricated and overheated, so adding oil when necessary is a nice skill to have in your arsenal.

Still, while adding gas is something that most drivers do on a weekly basis, adding oil isn't a practice that modern drivers know how to accomplish. This is especially true in the modern world when even for a simple bulb change, drivers bring their vehicle to the shop.

But you don't have to be that driver. Adding oil to your engine is easy and approachable, even if you've never done it before. With that said, there is more to adding oil than just opening the cap and pouring it inside. That will work, sure, but if you want to do it right, you will need to follow some steps.

For instance, many drivers often ask me whether they can put oil in a hot engine because they saw the light on the dashboard and are in a hurry. Like with most things in cars, the answer isn't as straightforward because there are many variables in play.

So, let's dive into the matter of adding oil to a hot engine because there is a lot to talk about here!

Why Engine Oil is Important

Engine oil is a crucial fluid that lets your engine run smoothly and efficiently while also ensuring its durability.

1. Lubrication

The oil is the lifeblood of your engine as it serves as a lubricant for all internal parts. Everything from the pistons to the crankshaft bearings and valves uses engine oil for lubrication. The oil creates a thin film between these parts, ensuring smooth movement and reducing metal-to-metal contact.

By minimizing friction, engine oil not only prolongs the life of these components but also maintains the engine at its peak performance, which results in higher power and better fuel efficiency.

Modern engine oils are asked to do many different things. They are designed to lubricate many different types of components, like bearings and piston rings, and retain their viscosity at cold and hot temperatures.

It sounds like a hard job, and it is, which is why I always recommend paying a bit more for higher-quality engine oil. A superior engine oil will ensure every part is optimally lubricated, thus prolonging the life of the engine more than if you used a cheaper oil.

2. Cooling

A lesser-known role of engine oil is cooling. A person that doesn't understand how engines work would think that it's the coolant that does that job, but while that's true, the engine oil is even more important for cooling.

Namely, the coolant takes care of cooling the engine block and cylinder head, while the oil cools the internal moving parts. Namely, the constant movement of the internal engine parts generates heat, which, if not managed properly, can lead to overheating and cause severe damage to the engine.

Engine oil circulates through the engine and absorbs and distributes heat away from critical components, thus maintaining optimal operating temperatures. The oil also cools those parts with its lubrication properties – a bearing would start melting if not lubricated, for example.

3. Cleaning and Protection

When the engine's internal parts grind against each other, they produce small metal shavings, and the combustion process produces byproducts that could accumulate in the engine. Moreover, although the air filter catches most of the debris from the atmosphere, some of it will still end up in the engine.

But that's not an issue because the engine oil will come to the rescue and clean the engine from all that debris. It contains detergents and dispersants that help suspend and remove these contaminants, preventing them from forming harmful deposits. Additionally, engine oil contains anti-corrosion additives that protect metal surfaces from rust and corrosion, further extending the engine's lifespan.

By circulating inside the engine, the oil also takes the dirt away from the moving parts, which is then captured by the oil filter. Therefore, it is always crucial to replace the oil filter at every oil change; not doing so could result in the dirt getting back into the engine and cause all sorts of issues.

Understanding Hot Engines

Combustion and friction lead to very high temperatures in the combustion chamber. However, thanks to the coolant and engine oil, the heat is dispersed throughout all other engine components and out of the engine.

1. What Constitutes a Hot Engine?

So, how hot does a car engine get? Well, considering everything is working properly and the coolant and oil are doing their job, the temperature varies between 190-220 degrees Fahrenheit (88-104 degrees Celsius). That is enough to get your skin burned, but also potentially cause other problems.

2. Why Adding Oil to a Hot Engine Can Be Problematic?

The engine's operating temperature brings me to the reasons why you wouldn't want to pour oil into a hot engine. Here is why you need to be extra cautious when doing that:

• Risk of burns: you could easily burn your hands or arms if you touch the cylinder head, engine block, and various pipes around the engine when it is hot. The risk is even higher when you add oil to a hot engine because you will need to be near those hot surfaces.
• Oil spillage: spilling oil on those hot surfaces is a fire hazard. While it is true that if you spill oil on a cold engine, it could still result in a fire when the engine gets hot, in that case, you will be able to clean the spill before anything bad happens.
• False oil level readings: when the engine is hot, the oil expands, just like every other liquid, making it more challenging to settle in the oil pan. Hence, you won't get accurate readings on the dipstick.

Can You Add Oil to a Hot Engine?

Sure, you can add oil to a hot engine if you are in a hurry. However, you need to be extra cautious when doing that. Here is what you should pay attention to.

If possible, wait for the engine to cool down slightly after turning it off – anywhere between 5-10 minutes would be fine. By doing this, you will lower the risk of getting burned and improve the accuracy of the oil level readings. Furthermore, I strongly recommend using a funnel when pouring oil inside a hot engine. The funnel will minimize spills and make the job neater and easier for you.

You should also check the oil level after adding some oil to ensure that you don't overfill the engine. Putting too much oil inside the engine is as dangerous as putting too little oil, as it can significantly increase the pressure inside and damage the internal components.

Repeat the process if necessary until you see the oil reaching the "FULL" level on the dipstick. Oh, and don't forget to clean the dipstick before checking!

Finally, you can greatly minimize the risk by wearing protective gear, like gloves and long sleeves.

Best Practices for Adding Oil to Your Engine

Adding oil isn't a complex process, but following the next practices will ensure the optimal performance and longevity of your engine.

1. Checking Oil Levels

Although every modern car is equipped with a dashboard light for low engine oil, I still recommend checking periodically. This is because the light only shows you when the oil reaches the minimum level, yet for optimal engine performance, it is recommended to keep it at "FULL" whenever possible.

Here is how you can get the most accurate reading out of the oil dipstick:

• Park the engine on a level surface: this is crucial, as an uneven surface can result in false readings.
• Allow your engine to cool down for 5-10 minutes before checking the oil level, as high temperatures can also result in incorrect readings.
• Locate the dipstick: its handle is brightly colored, and it is usually marked with "ENGINE OIL" or the oil pan symbol, similar to the light on your vehicle's dashboard.
• Pull out the dipstick and wipe it clean using a cloth or paper towel.
• Reinsert the dipstick fully into the tube, then remove it again to check the oil level. The oil should be between the minimum and maximum marks on the dipstick. If it's below the minimum mark, you'll need to add oil immediately. However, you should also add oil soon if it reads below the "FULL" level on the dipstick.

2. Choose the Right Oil

Choosing the right oil for your engine is crucial, as it ensures its smooth operation and longevity. Automakers test various oil types for every particular engine before finding a gradation that combines efficiency, performance, price, and durability.

You can find the correct oil gradation for your engine on the dipstick or inside the owner's manual. On some vehicles, you will be shown two gradations, with one usually better for hotter climates and the other one for colder climates.

The manual/dipstick will specify the oil grade (e.g., API SN) and viscosity (e.g., 5W-30). The oil grade, i.e., API specifications, are represented by a two-letter code, with the first letter indicating the engine type (S for gasoline engines, C for diesel engines) and the second letter denoting the performance level.

Meanwhile, the SAE viscosity rating measures the fluid's resistance to flow, meaning it determines how the engine flows through the engine at various temperatures. SAE viscosity ratings are typically represented by a number followed by the letter W (for winter), then another number (e.g., 5W-30 or 10W-40). This is known as the multi-grade rating system.

The first number represents winter oil viscosity, i.e., its resistance to flow at lower temperatures. An oil with a lower number would flow more easily inside the engine and is generally more desirable, especially if you live in areas with freezing winter conditions.

Meanwhile, the second number shows the oil's viscosity at high temperatures, like in the summer or during performance driving. In this case, a higher number is more desirable, as it ensures that the oil will maintain its protective film better at higher temperatures, reducing the risk of engine wear and damage under high-stress conditions.

3. Adding Oil Safely

Here are the steps you need to follow to add oil safely and effectively:

• Locate the oil filler cap: it will be situated on the top of the cylinder head and clearly marked with "ENGINE OIL" or the oil pan icon. Remove the filler cap and place it in a safe place – don't put it over the engine, as it could easily roll over and fall into a hard-to-reach area.
• Insert a clean funnel: doing this will minimize spills.
• Pour oil gradually: this is important, as you don't want to overfill the engine with oil. I recommend checking the oil in smaller increments and checking the level between additions.
• Remove the funnel and tighten the oil filler cap securely.

This video will show you the complete process to add oil to your car. Please check for a visual explanation.

Video created by CD How To

Properly Dispose of the Used Oil

Although you won't need to displace any oil when refilling, this is an important thing to note when you change the engine oil. Namely, oil is harmful to the environment and can reach the soil we get our food from, even if you pour it down the drain.

So, be responsible and collect the used oil in a sealed container and take it to a recycling facility or an auto repair shop. Some recycling facilities will even come to your place to collect the used oil, of course, at a price.

Conclusion

I hope that this article answers every question you have regarding putting oil in a hot engine. If not, please do not hesitate to ask me any further questions you might have. Also, be free to add something!

With that said, please be careful when working on a hot engine, as it is not a joke. Recently, a friend of mine spilled some oil on the hot exhaust manifold, which ignited the oil and caused a small fire. It was nothing serious, but it could've been if he spilled a larger amount. So, take your time, don't skip steps, and use protective gear!