Idea: Low Coolant Sensor to Prevent Head Gasket Failure on Gen 4 Prius

I wanted to float an idea here because I think it addresses a serious problem that a lot of Gen 4 Prius owners are facing.

As many of you know, when the coolant level drops, the check engine light doesn’t come on until you’re practically empty -- and by then, it’s too late. Within minutes you risk blowing a head gasket. (This is what happened to me). It seems unbelievable that Toyota hasn’t already solved this, but the fact is, there’s no early warning for low coolant.

My idea is simple: an aftermarket low-coolant level sensor that sits in the reservoir and alerts the driver before things get critical -- say, as soon as the level dips below the midpoint between “Full” and “Low.” A float sensor or probe could trigger a light or buzzer in the cabin.

The way I see it, this kind of kit could retail for maybe $100–$200. That’s pocket change compared to the $3,000–$5,000 cost of replacing a head gasket or engine. And there are millions of Gen 4 owners out there who might want the peace of mind.

So here’s my question:

Would you be interested in a product like this?

Do you think it’s worth pursuing as a DIY aftermarket kit?

Considerations:

Market potential

Target audience: Owners of Prius Gen 4 (millions of units worldwide) plus other Toyotas with similar cooling layouts.

Aftermarket appeal: This could be an add-on kit sold through auto parts chains, Amazon, or Prius enthusiast forums.

OEM potential: Toyota or other automakers might license or adopt it if shown to reduce warranty claims and engine failures.

Challenges

Sensor reliability: Coolant can be corrosive, and sensors must handle heat and vibration.\

Calibration: It must avoid false alarms (like when coolant sloshes around).

CARB/EPA considerations: If marketed in California, aftermarket add-ons sometimes need regulatory clearance (though a warning sensor is much easier than an emissions-control device).

That's all I can think of for now...

I’d love to hear what the PriusChat community thinks. If there’s real interest, I might take the next step and see about getting a prototype made.

Thanks,