Do Engine Cooling Additives Really Work? A Mechanic’s Guide to Summer Cooling Systems

Hagerty Media reader DUB6 writes:

Sajeev, I’m going to turn your high-powered investigative prowess onto a topic that might be appropriate, since warmer weather is right over the horizon. Some of us who drive older vehicles will be challenged with keeping our cooling systems working efficiently on summer cruises.

The Hack Mechanic set us straight on different types and colors of coolant, but in some cases, more help may be needed than just green, yellow, or red coolant. Should you turn to “wetter-than-water” additives? Do they work? Which are best? Are there pitfalls to avoid?

Sajeev answers:

I used a water-wetting additive decades ago, and it accomplished nothing in my specific application. But results vary by vehicle. My preference for fan shrouds, larger radiator cores, and heavy-duty fan clutches has helped future-proof my vehicles—including a 20-plus-year run with my Fox-body Fords. If overheating is a concern, I recommend these component upgrades first.

If upgrades aren’t an option and your cooling system is in top condition (no scale in the radiator, a healthy water pump, etc.), a “magic in a bottle” additive might help. Aftermarket products have likely improved since my early experience. I follow Project Farm’s lab-grade YouTube experiments, which found measurable cooling improvements with some aftermarket chemicals.

However, real-world results depend on location, vehicle, and driving style. What works in a controlled lab may not translate to the road. Balance is key.

After reducing cooling-system effectiveness to improve aerodynamics, I’ve learned that optimal thermal efficiency requires continuous monitoring. Done right, it leads to a better-performing vehicle.

I faced criticism on social media for sharing my results, with some fearing engine damage. That’s unlikely—my setup prioritizes factory cooling performance, and I use the vehicle as a commuter car, not a work truck.

How to Optimize Your Cooling System

Follow these steps in no particular order:

• Clean your radiator—flush it internally and clear debris externally to improve airflow.
• Clean your home AC unit’s radiator—it will run more efficiently in return.