What is the reasoning for NOT having a "low coolant" light in many cars?

October 27, 2019 12:36 PM

I drive a popular Japanese car from the previous decade, and am always in the habit of checking coolant levels since I appear to have a slow leak. Apparently this car does not have a "low coolant" light (like all cars, it has an engine temperature gauge/warning), and plugging in "low coolant light..." in Google will autofill with American and European cars, but no Japanese models. Of course, we can speculate about certain cars' reliability leading more people to Google them, but what's the reasoning behind many cars not having coolant warning lights?
posted by Seeking Direction to Travel & Transportation (4 answers total)

A low coolant indicator can only show that the fluid level is low. That's likely a problem, but so is having your radiator and reservoir full of straight water rather than a coolant mix. So a temperature gauge and warning light is a more useful indicator. A warning there could mean the coolant level is low, or that the mix is wrong, or that the thermostat is malfunctioning, or that the pump isn't working, or that the radiator is plugged, or that the fan belt is broken, or that a hose is broken. You don't want a warning signal for each of those. So you have one warning signal for the critical condition that ensues when any of those things happens.

All that said, it's a good idea to check the coolant level now and then. Same with oil, transmission fluid, brake fluid, windshield washer fluid.
posted by beagle at 1:01 PM on October 27, 2019

As beagle said, the temperature indicator covers more conditions than just low coolant, but it does cover low coolant.

The same goes for oil pressure indicator rather than an oil level indicator. The oil pressure indicator covers low oil level, but it also covers worn out oil pump or worn out bearings.
posted by JackFlash at 1:34 PM on October 27, 2019

It costs more to add a coolant level sensor in the reservoir and a warning light. It was not a consumer demanded feature in cars at the Camry/Accord price point and below. The sensors can and do fail (the float can stick or sink) which results in people needlessly freaking out when the warning light sticks on. Also, a car which has a warning light come on will be perceived as less reliable. For example, older Subarus [and Hondas and Toyotas] had no low oil level warning lights. I'm sure many people made it to the 5000 mile oil change interval with the car a quart down on oil (not low enough to cause damage) and were blissfully unaware of that. The oil is changed, topped up to full and it's all good. Now that Subaru has added an oil level warning indicator people are all incensed that "my car has the low oil level warning coming on! How dare you sell me this oil burning car? Class action lawsuit ahoy!"
posted by Larry David Syndrome at 7:53 PM on October 27, 2019

To expand on that a little more; your coolant temperature gauge and oil pressure warning light will let you know when you're critically low on coolant or oil. (Arguably, they will trigger too late.) They are not going to trigger with small fluid leaks / slightly low levels unless the small leaks are grossly neglected for an extended time.
posted by Larry David Syndrome at 7:58 PM on October 27, 2019