On The Road

Five-minute rule may save engine from catastrophe

A customer recently brought in his 2008 Toyota Sienna van after it had overheated. When we think a car has overheated, we ask some specific questions:

• How long do you think the car was overheating?

• Did you check the temperature gauge (if the car has one)?

• What was the temperature gauge reading at the time of failure?

Most modern cars’ instrument cluster (speedometer, RPM gauge, temperature gauge and fuel gauge) and interface screen (navigation, heating, air conditioning and entertainment) are becoming more and more intricate. People spend a lot of time learning about their interface screen but do not pay much attention to the instrument cluster – other than maybe the speedometer. When I ask people what their engine’s temperature was, most respond, “I have a temperature gauge?”

Check your gauges

I’m focusing on the temperature gauge in this month’s column, but the second-most important gauge is the oil light. Usually the same people who don’t pay attention to engine temperature do not pay attention to oil level, either. All cars have an oil pressure light, but not every car has an oil level light that indicates how much oil is left. This makes it even more important to check the oil level, because even if the oil pressure light does not turn on, the engine may be sustaining damage in a low-oil condition. The engine oil level should be checked regularly. Consult your owner’s manual for the correct procedures.

A majority of today’s cars still have a temperature gauge, but if your car doesn’t, it usually has a low-coolant light. Just as I stated above (for the engine oil level), if the coolant is low, the engine can sustain damage even before there is a major overheating incident. This is why it is extremely important to check your coolant level on a regular basis. You should always check your engine’s coolant level when the system is cold or the cooling system is not under pressure.

It is also important to check the expansion tank level and the radiator level if there are two expansion tank caps. The reason for this is if the radiator cap/expansion tank cap is not working correctly, you will have coolant in the expansion tank, but the radiator could be extremely low. Also, when looking at your temperature gauge, you will learn where the needle sits in the gauge. If the needle starts getting close to the red mark, or hot side (marked “H”) of the gauge, check the cooling system. Consult your vehicle’s owner’s manual for how to properly check the coolant level and your temperature gauge.

Engine coolant can leak many different ways and can have many levels of severity. There could be a small pinhole leak, seepage from a gasket or a more severe water pump or radiator leak.

Act quickly

In our customer’s 2008 Toyota Sienna, the water pump shaft failed and it lost most of its coolant quickly. These are the worst types because the engine can sustain damage quickly, without the driver realizing there’s a problem. The customer was not familiar with his temperature gauge and when the car started to exhibit drivability problems, he thought it was due to the heavy load he was carrying. Eventually the car stalled and he had it towed in.

The moment you think your car may be overheating, scan the instrument cluster for warnings. With an engine coolant-overheating problem, you only have approximately five minutes to react. If the temperature gauge is at half or getting close to three quarters, there’s still time, but as soon as it gets to the red mark, or the hot (H) line, you are down to five minutes. Assess your situation and take action. If you are in a safe area to pull over, do so and shut down the engine. Then wait for the engine to cool to check levels or make other arrangements.

The five-minute time frame is not a universal rule, but it should be carefully considered. The engines we see after they have overheated into the red usually have to be replaced. Luckily for our Toyota Sienna customer, the engine did not get severely damaged.

I urge all of you to take the time to check your levels and learn how to read your gauges. Remember that five-minute rule.

Matt Pataky owns Sunnyvale Foreign Car Service, 15 Pioneer Way, Mountain View. For more information, call 960-6988, email This email address is being protected from spambots. You need JavaScript enabled to view it. or visit sunnyvaleforeigncar.com.

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