Easy Formula for DIY Windshield Washer Fluid
Are you tired of paying a lot for windshield washer fluid? Have you ever considered making it yourself? In this post we go through an easy formula to make your own windshield washer fluid. You can even adjust the proportions as necessary depending on whether you need a summer or winter fluid!
Table of Contents
- Windshield Washer Fluid Ingredients
- Warm Weather Formula
- Freezing Point of Water/Methanol Mixture (by Volume)
- Freezing Point of Water/Isopropanol Mixture (by Volume)
- Freezing Point of Water/Ethanol (ETOH) Mixture (by Volume)
- Using Non-Pure Solutions
- Windshield Washer Fluid Recipe
- How to Add Windshield Washer Fluid
- Conclusion
Windshield Washer Fluid Ingredients
Windshield washer fluid is not complicated. It is simply a mixture of the following ingredients:
- Clean Water (for best results use distilled)
- Isopropyl Alcohol or Methanol
- Washer Fluid Concentrate or Dishwashing Liquid (1 oz)
- Blue Food Coloring (optional)
Warm Weather Formula
If you are operating in a warmer climate and will not see temperatures below freezing, then you do not need to worry about adding alcohol or methanol to your mixture. Add the other ingredients, but just use straight water.
Freezing Point of Water/Methanol Mixture (by Volume)
In order to avoid the washer fluid freezing in your vehicle, make sure that the freezing point of your mixture is below the lowest expected temperature your vehicle will encounter.
Below is a table showing the freezing point of pure water and methanol mixtures. Choose the appropriate % methanol using this table.
| Methanol (% Volume) | Freezing Point (F) |
|---|---|
| 0 | 32 |
| 10 | 20 |
| 20 | 0 |
| 30 | -15 |
| 40 | -40 |
| 50 | -65 |
Freezing Point of Water/Isopropanol Mixture (by Volume)
Isopropyl alcohol – also known as isopropanol – is commonly known as rubbing alcohol. You can use this instead of methanol, it will just require a higher concentration to prevent freezing. The table below shows the proportions for pure isopropyl alcohol. If you are using 99, 91, or 70% isopropyl, then adjust the mixture accordingly.
| Isopropanol (%) | Freezing Pt (F) |
|---|---|
| 0 | 32 |
| 10 | 25 |
| 20 | 20 |
| 30 | 5 |
| 40 | 0 |
| 50 | -5 |
| 60 | -10 |
| 70 | -20 |
| 80 | -35 |
| 90 | -70 |
Freezing Point of Water/Ethanol (ETOH) Mixture (by Volume)
Ethanol. You can use ethanol, it will just require a higher concentration to prevent freezing. The table below shows the proportions for pure ethanol.
| Ethanol (%) | Freezing Pt (F) |
|---|---|
| 0 | 32 |
| 10 | 25 |
| 20 | 16 |
| 30 | 5 |
| 40 | -11 |
| 50 | -26 |
| 60 | -35 |
| 70 | -54 |
| 80 | -74 |
| 90 | -101 |
Using Non-Pure Solutions
What if you are using a starting solution that is not 100% pure? For example, let us imagine you are using a starting solution of 70% Ethanol by volume (70% is ethanol and 30% is water). Use the following formula:
Starting Amount * [(Starting Solution %)/(Desired Solution %)] – 1] = Water to Add
Let us continue this example. If you have a 70% Ethanol solution, and you want to get down to a freezing point of -10F, using the chart above, we will want a final solution of about 40% Ethanol.
Let us assume we are starting with 1 gallon of 70% ethanol solution, then to get to a final 40% ethanol solution, we would plug in the following numbers into the equation.
Starting Solution % = 70%
Desired Solution % = 40%
Starting Amount = 1 gallon
Water to Add = (1 gallon) * [(70/40) – 1] = 0.75 gallons = 3/4 of a gallon
Windshield Washer Fluid Recipe
- In a clean 1-gallon jug, combine the water and methanol (if you do not have access to methanol, you can substitute rubbing alcohol or ethanol), using the proportions listed in the table above.
- For example, if your vehicle will be exposed to temperatures as low as -10 F, choose a mixture of 70% water and 30% methanol.
- Add 1 oz of washer fluid concentrate or dishwashing fluid such as Dawn or Joy.
- Add food coloring if desired. This step is optional and is mainly as a safety feature so that the fluid is not accidentally used for a different purpose.
- Seal the jug and shake lightly to mix (avoid suds).
How to Add Windshield Washer Fluid
- Pop the hood of your vehicle
- Locate the washer fluid reservoir (look for a water fountain icon on the cap)
- Open the cap
- Pour in the washer fluid
- Close the cap
For more details on specific vehicles, check out these posts:
- Toyota Corolla – How to Add Washer Fluid
- Toyota Sienna – How to Add Washer Fluid
- Honda Accord – How to Add Washer Fluid
Conclusion
I hope you found this recipe helpful!
How is this recipe cheaper than buying premade wwf? The cost of the methanol or alcohol being added to the water mixture is more expensive then premade wwf.
The math in the “Water to Add” formula isn’t making sense.
70/40 = 1.75
1.75×100 = 175
175-1 = 174 not 0.75
It looks like the x100 is the issue
You’re right, thanks for the comment. I’ve changed it now!
so if I am using 70% etoh or 91% etoh in -10 weather. I need what ratio of etoh to water? Table seems to be confusing as your eg is for methanol. I would need 70/30. Etoh/water ?
Good question! You would want a ratio of 0.75 water to ethanol solution. I added a section to the blog post, hope it helps.
How does Methyl Hydrate compare to Methanol, regarding freezing points, and freezing point by volume mixed with water?
(I can’t seem to find any clear, or consistent, information on the subject. What little information I do find is contradictory to each other. One source will say they’re same thing, or essentially the same thing, while another source will say that they are similar but still two different chemicals, yet another source will say they a definitely two distinctly different chemicals! So…….???? Here I am, no closer to a correct answer.)
Hi Kit,
Great question! There does appear to be some confusion out there regarding these terms. People tend to use these two terms interchangeably, so for most cases people are referring to the same thing.
However, the term “Methyl Hydrate” is not really a correct and rigorous term for Methanol.
The “hydrate” portion of the term suggests there is a water molecule attached, and in fact, this compound can occur naturally deep in the frigid ocean, so it does exist.
But this compound is not what most people are referring to when used in a context like this. They typically mean Methanol.
So, the short answer is: they are technically different, but usually when the term Methyl Hydrate is used, it is being used incorrectly to mean Methanol!
I hope this helps and doesn’t “muddy the water” any further!
All the best to you,
Richard
Thank you – – – I knew it should be simple – – -/ Ron, in LODI