How to Diagnose and Fix Low Coolant Warning for Audi (A3 8V) / VW


Hey guys! Matt Popovich here. Today in my series of Audi A3 tutorials, I’m going to explain what it means to have a “low coolant” warning and how to fix it from the prospective of a 2015 Audi A3 8V. When you first start your car, beeps and chimes will start going off like your car is very unhappy with you, but don’t freak out as it’s not the end of the world yet… although it could be if you don’t keep an eye on things.


  1. Check the coolant temperature indicator
    • If it stays in the middle, you are fine to keep driving.
    • If it goes above the middle, you will want to pull over, shut the engine off, and add coolant (if low).
  2. Check coolant reservoir level
    • The coolant reservoir is on the passenger side of the engine bay.
    • When the car is cold, coolant should be between the maximum and minimum line. When the engine is warm, the coolant can rise to be slightly above the maximum marking.
  3. Add coolant
    • Use G13 coolant as stated on the reservoir. Cut coolant concentrate 50/50 with deionized water (also known as DI water) or distilled water.
      • The manual states that you can also use G12++, but I will follow what is printed on my reservoir.
      • Do not use tap water.
  4. Done
    • You do not have to reset anything in the car for the low coolant warning to go away. Once you drive it again, the sensor should read the coolant levels and the coolant light should turn off.

First steps: can you keep driving?

Audi A3 8V Dash Engine Temperature Gauge Location of the Coolant Temperature Indicator (Highlighted)

Note that if you have an S3/RS3, the coolant temperature gauge is replaced with a boost gauge. You can find the S3’s engine oil temperature by following this video. This video will show you how to modify an S3/RS3’s settings via OBD2 to add engine oil temperature to the instrument cluster. However, oil temperature is different from coolant temperature, read this article for a good explanation.

The first thing you’re going to want to do is to keep an eye on your coolant temperature indicator. Coolant has two functions: it keeps the engine from overheating and it protects the engine from freezing in the winter. I just started my car after it was sitting for a ~day so the engine is cold. After a few minutes, the coolant temperature will creep back up to the normal level, which is where it should be while you are driving. It’s “okay” to keep driving with the low coolant light on as long as your coolant stays at normal operating temperature. You’ll need to keep an eye on it. Ideally, you’ll want to check the physical, liquid coolant level as soon as you can for some additional peace of mind. If the coolant doesn’t get to normal operating temperature or if it goes past the midpoint line, that’s a bad sign and you should pull over, open the hood and check the coolant level in the coolant reservoir. Let me show you how to do that now.

Checking the coolant level

First, open the driver door so that we can pull the lever to pop the hood. We will want to park on a level surface so that the coolant in the reservoir isn’t tilting to any side. Next, we’ll go around to the front of the car and feel under the hood, above the Audi symbol for a button or latch to release the hood. From here, we can find our coolant reservoir which will be on the passenger side of the engine.

Audi A3 8V Coolant Reservoir

As we can see, my coolant is below the minimum line, so we’ll need to add some more. When the car is cold, coolant should be between the maximum and minimum line. When the engine is warm, the coolant can rise to be slightly above the maximum marking. As it is right now, it’s “okay” for me to drive with the coolant level below the minimum line, as I do have coolant in the reservoir, but I need to keep an eye on the coolant temperature indicator while I’m driving.

Which coolant to use?

Audi A3 8V Coolant Reservoir G13 Symbol

For coolant, I need to use G13 coolant as stated on the reservoir.

The manual states that you can also use G12++, but I will follow what is printed on my reservoir. While you can technically mix the two, it’s not ideal. If you want to switch from G12++ to G13 or vice versa, you should flush all of the old coolant out first (“When changing fluid types to a newer fluid, you must flush the old coolant out”).

G12++ and G13 will be pinkish / purple in color. Do not mix it with any blue, green, orange, yellow, or any other colored coolants as they are not compatible. Coolant can be bought as either concentrate (100% strength concentrate) or as diluted or mixed (50/50 concentrate and distilled water). If you buy concentrate, you will need to cut the strength yourself with distilled water. Do not use tap water, do not use bottled water. Use distilled water.

After further research, it appears that deionized water (also known as DI water) is preferred over distilled water for mixing. However, due to its cost ($18/gallon, affiliate link), and the owners manual stating that “mixing the coolant additive with distilled water is recommended”, I will continue to use distilled water ($1/gallon, affiliate link). Moral of the story: deionized water > distilled water >> tap water

Owner's Manual Note on Adding Coolant

Side note: If you’ve ever heard the term “antifreeze”, that technically refers to concentrate whereas “coolant” technically refers to the 50/50 mixture of concentrate with distilled water. They’re sometimes used interchangeably but while doing some research, I learned that they are technically different.

I will be using OEM coolant, which is the coolant that the original equipment manufacturer (aka Audi) uses. You’re probably fine using off brand G13 substitutes but I personally think coolant is cheap enough that I won’t be using an off brand (prices and links below). The OEM coolant is Pentosin Pentofrost E:

You can get distilled water from anywhere, most grocery stores carry it (and I have links below).

When you mix it, you don’t have to go full Bill Nye with it to make sure it’s a perfect 50/50 ratio. The manual states that the concentrate should be at least 50% but less than 60% of the solution. If you’re in a place with extremely cold climates, it wouldn’t hurt to be closer to 60% concentrate. I’m going to go half Bill Nye and eyeball my solution.

Pentosin Pentofrost E 1.5L Container

Adding coolant

Now that we’ve made our coolant, we need to add it to the reservoir. Before you open the reservoir, make sure you let the engine cool down. Do not open the reservoir when the engine is hot as coolant will typically be around 200°F (93°C). So to prevent burns, let the engine cool down beforehand. If you can’t or don’t have time, use a large, thick cloth to open the reservoir to protect you from escaping coolant and steam. Be careful not to get drips anywhere as ethylene glycol (AKA coolant) hitting a hot engine can catch fire under certain circumstances.

Hot Coolant Warning from Owner's Manual

Once open, add your coolant to get you between the min and max lines. Do this slowly, especially if the coolant tank is empty so that you don’t trap any air in the line. I decided to take the anti Bill Nye approach and it required multiple refill attempts to get me between the lines… “Our actions have consequences”.

Wrapping up

Now that we’re topped off, make sure you fully tighten the lid and hear a click. We need it to be fully sealed so that none of the distilled water can evaporate and be a source for escaping coolant. Speaking of this, the coolant system is a sealed system. No coolant should be able to escape. Thus, if you’re low on coolant, that suggests a problem. If you have to add coolant regularly, you should get that checked out as you probably have a leak somewhere in the system. Regularly, as in every couple of weeks. If you need to add coolant once or twice a year, it’s not a huge deal as coolant is pretty cheap to add, but again, you shouldn’t have to do that because it is a closed system.

Once we close the lid, we’re free to drive off and keep an eye on the coolant temperature indicator, but our work here is done. You do not have to reset anything in the car for the low coolant warning to go away. Once you drive it again, the sensor should read the coolant levels and the coolant light should turn off.


That’s a wrap! Hopefully this helped. If there’s anything I missed, feel free to let me know in the comments. I’m working on a whole series of Audi A3 videos and posts, so feel free to check some of those out as well. Thanks for reading! I’ll catch you in the next one.




Disclaimer: Matt Popovich is not a mechanic nor a chemist. Please do your own research and consult with a professional before attempting any DIY repairs. Matt Popovich assumes no liability for property damage or injury incurred as a result of any of the information contained in this video. Matt Popovich does not provide a warranty for any of the listed information and does not guarantee any expressed or implied result. Use this information at your own risk. Matt Popovich recommends safe practices when working on vehicles and or with tools seen or implied in this video. Any injury, damage, or loss that may result from improper use of these tools, equipment, or from the information contained in this video is the sole responsibility of the user and not Matt Popovich.

This post is licensed under CC BY 4.0 by the author.

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