Can You Add Oil to a Hot Engine?

by Synthetic Oil | Last Updated: January 29, 2023

A warning light comes onto the dash and you begin to wonder if you need to change your oil. So you stop at the local auto parts dealer, grab some motor oil, and get ready to add the oil. But then you stop. Can you add oil to a hot engine? Or would doing so result in engine damage? The short answer is yes, but there are various factors involved that you need to know about first.

If you are unsure of what those factors may be, you have come to the right place.

**Note** – A quick hello to anyone reading this, I’m Alastair and this is my site Synthetic I started this site to help people with their oil questions, and hopefully what you’re about to read will help answer your questions. This page may include affiliate links to the likes of Amazon, which if you make a purchase I qualify to earn a (typically small) commission. Don’t worry as this won’t cost you anything, the likes of Amazon pay any commissions. Thank you in advance for your support as this helps bring you more (hopefully) helpful content.

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Can You Add Oil to a Hot Engine?

While you can add oil to a hot engine, it is not often recommended for a complete oil change. Most of the time people will add oil to a hot engine when they need to top off their motor oil. Otherwise, you should always wait about 20-30 minutes after shutting off the vehicle before measuring the oil level or conducting an oil change. Waiting is important because you have a better chance of receiving an accurate measurement.

Plus, engine oil gets very hot (around 230-260°F or 110-127°C), and you probably don’t want to get burned.

How Does Engine Temperature Affect Oil?

Motor oil outside of an engine may look and behave differently than what is inside when there is a temperature difference. In short, the temperature of an engine affects the viscosity of the oil. When the engine is hot, the oil inside is thinner. While this is good for the engine, it can make it more difficult to determine just how much oil is present in the engine. If you try to read the oil level on the dipstick while the motor is still hot, the reading may be inaccurate.

Conversely, when the engine has been sitting for some time, the oil will be thicker. Oil will expand and contract, but synthetic oils are more likely to do this than conventional oil.

What Happens If You Add Oil to a Hot Engine?

As mentioned previously, topping off the oil when you have a hot engine is sometimes necessary. You should be fine, just try not to spill any oil on the engine parts.

Here is the thing, when an automotive technician has your car for an oil change, they will warm the engine slightly. Cold oil takes longer to absorb heat in the engine. In other words, there is not much danger involved here.

The thing you want to keep in mind is the level of oil. You should never go over the maximum amount shown.

What is the Correct Temperature for Adding Oil to an Engine?

According to NAPA, the best engine temperature for topping off or changing your oil is around 100 degrees F (37 degrees C), but you can add oil to your engine whether it is hot, warm, or cold. Whichever way, nothing concerning will happen.

That said, you should avoid topping off or changing the oil when it is either extremely hot or cold outside. For instance, if your car has been sitting all winter and the temperature outside is freezing, you should not change the oil without warming the engine first.

What About Adding Cold Oil to a Hot Engine?

Cold oil is safe to add to a hot engine. You need not worry about the oil adversely affecting the vehicle. The only time you want to be careful is when the outdoor temperature is cold, too. Sometimes, when the temperatures dip, synthetic oils can become thinner, so you may accidentally end up adding too much oil to the engine.

Can I Mix Oil Types?

What happens if you need to top off oil during a road trip and only have a few half-filled bottles of oil in two different weights? Can you mix them in a hot engine? Mixing oil brands may be OK, depending on the brand, but you should be careful when mixing weights. Even if adding oil to a hot motor won’t cause problems, the change in engine oil viscosity may cause performance issues.

Final Thoughts

So can you add oil to a hot engine? Yes, you can! Ideally, you want to let the car sit for about 20 minutes before you start working with the oil directly because you risk getting burned. Otherwise, it is perfectly safe to top your motor oil off while the engine is still relatively hot. Putting oil in a car while the engine is hot will not damage the motor or affect the oil.

Now that this question has been answered, why not double-check how long a car can go without an oil change?