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On the Road

What’s that liquid? Tips to tell if a truck is leaking coolant

David Sickels is the Senior Editor of Fleet Equipment. He has a history of working in the media, marketing and automotive industries in both print and online.


If your driver is out on the road and notices liquid is leaking from the engine area, they might suspect it’s a coolant leak, but how can he or she know for sure?

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Here is a transcript of the video:

Complicating matters is that coolants are available in different colors, so it can be hard to just look at the color of the fluid to identify what it is. Plus, since today’s newest engine designs tend to be quite complicated, it is now very difficult to determine what product or what type of functional fluid – like coolant, brake fluid, power steering, transmission fluids, or motor oil – is actually doing the leaking at a glance.


And, it’s important to catch coolant leaks early, because coolant leaks don’t just reduce the coolant level of the truck, it can potentially lower coolant pressure and lead to air entrapment in the system, and that can lead to engine overheating, lower MPG and increased emissions and corrosion.

So, if you think your truck is leaking coolant, one of the first things you’ll want to check is whether you have a broken radiator cap. Some applications experience evaporation either through coolant hoses or due to a faulty radiator cap, and in these cases, water will evaporate out and you’ll notice the coolant level dropping.


Another situation is corrosion in the radiator or build-up in an engine block cooling system passage. Build-up or corrosion throughout a system can break free and clog key areas, and that can cause the engine to overheat. This will result in coolant boiling and the cooling system pressure increasing above the designed pressure. The excess pressure will cause steam to vent out of the radiator cap, causing a loss of fluid in the system.

But what if it still isn’t clear if the liquid leaking is coolant?

Well, another way to find out is by looking to the results of the engine’s most recent used oil analysis report. Some coolants have potassium, while others use sodium. If you notice sodium and potassium are present in noticeable concentrations in the report, this is a sign that coolant is attacking the aluminum. And, this is a clear indicator that there is a coolant leak.


In any case, one of the most important things you can do is to check your trucks’ functional fluid level and condition routinely, and to add fluids as needed in accordance to engine and vehicle manufacturing recommendations, or your fleet maintenance protocol. If a fluid level does need to be corrected, this is the time to inspect the entire system by tightening coolant, brake and power steering fluid caps, hose clamps, connectors and elbows, and check for leaks while you’re at it.



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