6 Hidden Dangers of Mixing Red and Green Coolant You Need to Know Now!

My car’s coolant is usually colorless, though I sometimes get dyed coolants. Of course, the dye isn’t necessary for the coolant to work. Nonetheless, it makes it easier to differentiate coolant types and catch leaks early on.

So, does mixing red and green coolant pose any risks? Yes, green coolant is ethylene glycol, and red coolant is propylene glycol. Mixing the two clashes their specific coolant formulas, causing:

• Gelling and clogging
• Overheating
• Reduction in freeze protection
• Reduction in corrosion resistance
• Seals and gaskets wear (on water pump and cylinder)
• Erroneous freeze point readings

Learn more about red and green antifreeze and why mixing the two is a bad idea. Plus, I’ll tell you what to do if you mix them somehow.

Comparison Overview Between Red and Green Coolant

Before I dive into the risks, allow me to highlight the differences between the two antifreeze.

6 Risks of Mixing Red and Green Coolant

Here are the risks posed if you mix red and green coolants together.

1. Gelling and Clogging

Ethylene and propylene have different chemical structures. So, the additives in each antifreeze are formulated for their specific base glycol. Mixing the two means you have inconsistent additives and different base glycols in the blend.

Over time, the two coolants will react. Additives, primarily silicates, will drop out of the solution as the hydrogen bonds into the gel. This forms a semi-solid gel or brown sludge in a coolant reservoir. It will clog your radiator, hoses, and heat control valves.

2. Overheating

As I mentioned above, sludge/gel formation will clog your system and restrict coolant flow. Therefore, the coolant will be less efficient in transferring and circulating heat away from your engine.

Moreover, the boiling point of a mixed coolant solution is lower than non-mixed coolant. Hence, the mixture will vaporize at a lower engine temperature, causing overheating.

3. Reduction in Freeze Protection

Ethylene glycol and propylene glycol have different abilities to depress the freezing point of water when added. Therefore, a mixed solution causes a higher freezing point than using only one.

Also, sludge formation removes glycol from the solution. This increases the percentage of non-freezing water in your coolant. Higher water content raises the coolant freeze point.

4. Reduction in Corrosion Resistance

Each coolant has a precise corrosion inhibitor for the specific glycol base and metal components. Essentially, each one is buffered to an ideal pH to protect against acid corrosion that results from oxidation.

So, when you mix two coolants, the pH will move outside the optimal range. Additionally, sludge formation removes corrosion inhibitors from the solution. This exposes metals in your cooling system to more corrosive conditions.

5. Seals and Gaskets Wear (Water Pump & Cylinder)

I already mentioned that mixed coolants will disrupt the pH balance. The resulting solution can be more acidic or alkaline. Thus, it will eat away rubber seals and gaskets over time.

Plus, incompatibility uses up corrosion inhibitors faster. Without protection, the metals will corrode more and physically abrade the seals. You’ll typically have leaks in the long run.

6. Erroneous Freeze Point Readings

Your refractometer only measures freeze point depression based on coolant glycol concentration. Essentially, it assumes a single glycol type.

So, when you blend two glycols, their individual freeze point-lowering effects offset each other. This is because of the different freeze point depression properties.

Basically, the overall glycol concentration reading will be inaccurate. Your refractometer won’t account for both glycols present. Moreover, any sludge or precipitate formation will skew readings by removing glycols from the test solution.

Flushing and Refilling Your Cooling System With Proper Coolant

Typically, there are two remedies to mixed coolants:

• Coolant flushing
• Drain and fill

I know it may sound like the same thing, but they’re actually different. So, coolant flush vs drain and fill – what’s the difference, and which one’s better?

In a coolant flush, you pump water and a flushing product through your entire cooling system under pressure. I recommend the BlueDevil Radiator Flush for its advanced cleaning power. After flushing, refill with new coolant.

The flush method is more thorough as it removes dirt, rust, and sludge. Such contaminants may degrade the new coolant. Typically, you should flush the system every 5 years or if your car has overheating issues.

Drain and fill means simply draining the old coolant and refilling a new antifreeze. This method doesn’t remove old coolant sludge and rust. Only do it on newer vehicles or simple coolant changes where the system is clean.

Here are the steps for coolant flush:

See how to flash the cooling system of a car in the following video for a clear visual understanding.

Conclusion

Mixing red and green coolant, or any other coolant of different colors, is often a bad idea. It can compromise heat transfer, damage cooling parts, and eat away critical engine parts. Of course, it may not be catastrophic in the short run, but you need to act fast by flushing your system as soon as convenient.

But in some rare cases, two similar coolants may have different colors. So, I’d advise checking the label. If they’re of the same formula as the coolant already in your car’s system, you’re good to go. However, avoid generic coolants unless approved.