2012 Prius Coolant Temp Light and losing coolant

Welcome!
Sorry to hear it, but it does sound like the head gasket unfortunately.
Keep in mind that the brake actuator could be next, also very expensive, and the inverter.
If you love your car, a new engine would be best, especially gen 4 if you can find someone to install it.
Head gasket is okay, but you need an expert to make sure there is no other engine damage.
If you can afford a new (er) car, that might be best.

 

I would take a chance and replace the engine water pump and fill it up with new coolant. Then see how it runs for a week or two. You definitely have a bad water pump. The coolant is probably being pushed out of the plastic reservoir. Look for evidence of dried coolant around the reservoir.

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In New Jersey with careful shopping the engine supplier is in your state You should be able to get this done for about $1,900 maybe just a tad more That's an engine replacement with a JDM spec replacement from the engine importer right down the street from you in New Jersey.

 

You can certainly give that a go with the small leaks that these things develops a lot of people think that's a possibility Don't do it as my recommendation even with the latest orange label stuff I'll have to go out to the shop and take a picture of it and give you the name of it I wouldn't even use it a distributor came by here and gave me a whole spiel about it and I looked at him like it was out of his mind but he left two bottles and he really told me I should try it blah blah blah. Usually most all iterations of that kind of nonsense clogs up the ways and radiators heater cores things that you need for your car to work like you've expected and it has been once you plug up these ways in these devices like radiators and heater cores things get worse and then the head gasket sure enough erupts quickly I don't know where you are in the process You can try taking some of the pressure off the degas tank which is essentially your radiator jug You open the jug turn it over the cap You see the o-ring take it off with a scratch off put it in your armrest screw the cat back on now instead of building up 15 PSI of pressure or whatever builds up in that container It will not coolant will still circulate but it will not be under pressure so you will not get the added benefit of the pressure which is necessary generally speaking but in a Prius believe it or not it will take a lot to overheat the vehicle like traveling down the interstate for distances going to work and back and what not unless you're running Uber eats or something like that that's a whole different ball game but going back and forth to work 10-15 mi you could stave off doing the head gasket for probably months but no 4-hour trips down to the beach. The labor to replace your engine to be honest about it and most places in the country unless you're dealing with some high dollar people should be around $800 You supply the fluids oil Asian red coolant so on and so forth any hoses that are deemed needed to replace etc.

 

You say you're losing coolant so on the bottle you see the full mark how many days does it take for you to get off that full mark or hours? These are important things you need to know

 

Please read what I wrote in post #3 above. It is much cheaper to replace the engine water pump than guessing that you have a bad head gasket and spending a lot of money replacing the head gasket or for a replacement engine.

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A Toyota dealer diagnosing a head gasket using a hydrocarbon gas test is definitive. The problem is too common on these years. Their dealer pricing is ridiculous when you could have a rebuilt motor shipped from California and installed for less than their head gasket price. An engine that has overheated several times is a poor risk for minimally invasive surgery (eg a head gasket alone) and does not upgrade the pistons and rings.

Sealant is a short term fix assuming it works at all. Perhaps a week, a month or a couple of months. You are risking the radiator and heater coil. The heater coil is expensive to fix since the dash has to come out.

Changing the water pump for $300 at an independent who ONLY uses oem parts is a possible step IF the engine has never severely rattled on startup, which is the typical head gasket symptom even before serious coolant loss and overheating has occurred. In fact many gen3 head gasket fails never overheat.

Otherwise I would find an independent to install a pro built rebuilt engine even if it has to be shipped to you. Not everyone will do this but it’s the best value if you want to keep the car longterm.

 

Yes new water pump, thermostat, full EGR cleaning, intake and throttle body clean, fuel injectors, new PCV, plugs...everything. The problem with JDM engines is they have the same gasket as you had before and there's no way to tell if it's even already starting to leak. Good luck, hope it works for you.

 

Only oem. Your old oem may be better than a new aftermarket.

 

Yep OEM only.

 

all the best!

 

Congratulations! It will drive better with no Shake, Rattle and Roll.