DIY: How to check and test your coolant


Most people know to regularly check engine coolant levels in their car, but what some don’t realize is that coolant breaks down over time and eventually loses its ability to protect your engine and radiator. So for this DIY episode, Hagerty’s Randy Clouse walks you through how to test your coolant and on our 1969 Chevrolet Camaro SS.

This is a companion discussion topic for the original entry at https://www.hagerty.com/articles-videos/articles/2018/02/09/how-to-check-your-engine-coolant


Surprised at no mention of checking the freeze/boiling point of the coolant? It’s the first, and in my mind the most important thing I look for when checking coolant. I always run the mixture around -40 C/F.


One of my cars is particularly sensitive to coolant going acidic so I just change it annually as part of a routine when it comes out in the spring. I think bi-metal engines are even harder on coolant. My old car which is all cast iron seems to be slower to go bad.


I read this a while ago, any truth in it?

Use a volt meter. connect the + to ground and use a screw driver or other, like a piece of wire, and connect the - lead to it. dip it in the coolant without touching the radiator metal. if it reads a half volt, the coolant needs changing, if its making .4-.5 it shoud be drained and replaced with fresh after a good flush.


@woodenshoes - Your bring up a good point. Checking the freezing point of the coolant is important, especially if you don’t have a heated storage location or the vehicle is driven in conditions of freezing temperatures.

A simple draw of fluid using a hydrometer can show the freezing point in short order.


@kenttt - From my understanding, the process you describe is a way of testing for electrolysis in the system. Electrolysis can amplify corrosion in the cooling system and cause premature failure on cooling components.

This test doesn’t tell you about the coolant so much as the charging system or grounds. If there is static electricity in search of a ground, poorly grounded engine components or an over-charging alternator they can cause the coolant to show voltage.

It is best to flush the coolant if it fails the test as you describe it, but additional diagnostics would also be needed to find the root of the problem.


Regarding the use of a multimeter to measure voltage. A multimeter is for measuring voltage. There is NO voltage between the vehicle ground and the radiator or its contents. If there is there IS an electrical problem.

This voltage measurement is a questionable procedure. If it is valid, please provide the multimeter settings for this “voltage test”

All that said.


The Meter should be set to “Ohms” (not Volts) this will measure the “Conductivity” of the coolant.
High conductivity (ie lower resistance) would mean the coolant has lots of contaminants and should be replaced.
This is a common test for Water Purity and can be researched on line.


I didn’t know these test strips existed and just ordered some. Looking forward to keeping an eye on my summer car and scooters, which probably don’t get coolant flushes often enough.


Perfect. Conductivity makes sense. Ohms, or resistances, will indicate how much conducive materials is in the coolant. Over time the coolant will absorb conductive metals form the engine and lower resistance. Thanks for the clarification.

Finally, as a note, to reduce corrosion in a coolant system is benifical to install a anode design for this purpose. An anode will reduce corrosion of all engine cooling parts significantly and is a simple and inexpensive addition to any classic’s cooling system.

I have installed a zinc anode in all the classic cars I own for less than 20 bucks each and inspect them every couple of years to ensure they working and replace them when necessary. They work great. It seems that few classic car owners take advantage of this simple recommendation.