Car ownership 101: How to diagnose engine cooling problems

This requires immediate attention
by Paulo Rafael Subido | Aug 19, 2018

Erratic engine temperatures? Needing to top up the radiator every morning? It is time to inspect the engine cooling system. Case study is my brother’s Honda Civic. The hatchback has been showing inconsistent temperatures after a major overheat. Something happened and the engine was never quite the same. It was time to solve the problem once and for all.

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Difficulty level

Medium. Your diagnosing skills will be tested

Things to remember

-Modern cars can go a year without requiring to top up the radiator. If your car is losing coolant, this is a sign of a problem.

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-Never keep driving a car that is overheating. This may lead to catastrophic damage. Call a towing service.

The gear

- The necessary tools

-Eye and hand protection

-A place to work

Important things to check

-Take the necessary precautions when opening the radiator cap of an overheating engine. This procedure is very dangerous. Never open a radiator when hot

Here's how to diagnose an overheating engine:

1) Check the fans

The first thing that I checked was to make sure that the auxiliary fan activated when the engine hit operating temperature. It was not. So, what we did was find the auxiliary fan switch located on the temperature sender, pulled it out, and bypassed the switch by making the fan run by connecting it straight to the battery. The fan switched on, meaning the motor works. It was the fan switch that was defective. I replaced this with a working part from a surplus shop. 

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2) Examine the external coolant routing for leaks or damage

The next issue was to replace the thermostat housing which had a small hole on it where water escaped. We had patched it up with some epoxy, but it’s better to just replace the part outright. With that done, it was time for a test drive.

3) Could it be the radiator?

The temperature still spiked during a test drive. The radiator was the next suspect. The water inside was quite rusty already, and the core was still the original from when the car was new. We scored a brand-new replacement radiator. The car seems to be running fine. For now...

4) The head gasket might be the problem

Opening up the radiator during start up revealed bubbles in the coolant. Oh no. This means that combustion chamber gasses have found their way into the cooling system. This is the sign of a blown head gasket. Watch this space for updates on how what goes on when a head is pulled from the engine.

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PHOTO: Paulo Rafael Subido
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