If you look in your owners manual that is probably a Low Oil Pressure light , not a low level light. That manual will also say something like check oil level at every fuel fillup at least .
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Which is it?
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I just looked at the manualâŚit looks like you have a low oil pressure warning that will come on, not a low oil level light. If the low pressure light comes on, youâve already run it way too low and caused engine damage.
Itâs unusual if you want to keep a car for a long period of time/miles. Oil is super quick and easy to check once a week or every 2 weeks/month depending on how much oil your car burns.
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I check the oil in both of my cars every Saturday morning, regardless of when the oil was last changed.
Iâve also taught my daughter, who recently started driving, to check her oil every Saturday. Itâs a good routine to be in.
Itâs also cheap insurance. Waiting the have the mechanic check the oil level until you change the oil is a foolish thing to do, in my humble opinion. The engine burns and/or leaks oil silently, and you have no way of knowing until itâs too late. And by the time the âoil lightâ comes on on your dash, itâs generally too late.
Good luck.
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I wish you happy motoring, but given your attitude, results may varyâŚ
Let me only suggest that the unofficial name for the dashboard light you are referring to is âthe idiot lightâ⌠and thatâs for a good reason.
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And by your own admittance you donât know much about cars. The conclusion youâve come to is based on what one person said. That does not mean that your mechanic is correct by default.
There is a difference between a oil pressure warning and a light that indicates a lack of oil quantity
Probably because your oil pressure has never dropped below whatever threshold Toyota determined it should be. Again, you can have decent oil pressure with the oil level still being significantly low.
Most people who take a vested interest in their vehicles do. I check the oil on my cars about once or twice a month, typically after theyâve been sitting overnight.
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You mean idiot light right by the time it comes on it is usually to late or the idiot looking at it has no idea what it is 
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Given the added info about the lack of oil situation and the OPâs laizzez-faire attitude about it I donât think the car is worth dinking with except as a DIY project and that is obviously beyond the OPâs abilities.
That oil light on the dash only has to illuminate one time to cause damage. Itâs often called an âoil pressure lightâ but the correct terminology is âNo oil pressure and your engine is a nano-second away from being off of life support and chunking a few rods through the block lightâ.
Even with the light off that does not mean things are kosher.
Could fix it with the same material used to fix CELs; a strip of electrical tape. Couple of cotton balls for the ears to drown out the knocking and good to goâŚ
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Iâm certain your Owners Manual says to check the oil every time you get gas.
Virtually every manual says this.
Itâs the prudent thing to do until youâve determined how much, if any, oil the engine consumes.
Once I know an engine isnât consuming enough oil to need topping up I stretch the checks out to every 1000 miles.
For me that can take anywhere from 3 days to 3 months (or more since the pandemic).
Itâs an easy number to keep track of on the odometer.
Iâve never owned an oil burner, but Iâve done this with every car Iâve owned.
When an engine is run while low on oil the remaining oil has to work harder.
It gets dirty faster and gets hotter, increasing wear, which increases consumption.
Itâs a vicious circle.
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My guess is thereâs a problem with the piston rings, which allows oil into the cylinders, which then gets burned and is clogging the engine w/carbon. If so at the very minimum the piston rings will have to be replaced. And since the engine has experienced periods of very low oil levels, there are likely serious engine problems beyond just the piston rings. Iâm guessing the engine is shot and you need a new engine to ever resolve this situation.
Ask your shop if it would make sense to replace the engine with a used engine, from a wrecked Prius but an engine in otherwise good condition. If thatâs not feasible, this car appears destined for the auto-crusher, and OP will be purchasing another vehicle.
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If the car was in running condition, it would be worth a lot more than $5k right now. It will also cost a lot more than $5k to buy a similar used car right now. It makes sense to replace the engine, and take better care of the car in the future.
2012 Prius Warranty and Maintenance Guide is available online at the Toyota website. Owners are supposed to check the oil level once a month. Hopefully, your engine has not suffered severe damage, but at least now you know to check it once or twice a month and keep the oil level full for the next vehicle.
âWith 1 exception, I donât know anyone in my family, friends, or professional contacts that personally checks their own oil level.â
That comment pretty much says it all and explains why the OP has engine trouble now.
And one can safely bet that when an engine goes south any and all of them will get upset and blame the car manufacturer or a mechanic for trying to rip them off.
âIâll never buy another rotten POS (fill in the car make) againâŚâ.
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well, the supply of manufacturers shrunk over the last decade, but yet long enough to let one to continue the journey:
Because you arenât being clear and consistent in what youâre telling us.
Thatâs a common misconception, but itâs wrong. That is an oil pressure light. It will tell you if the oil pressure drops. This can be caused by oil that is so low that itâs fallen below the pickup tube and isnât getting circulated. But by the time that oil light comes on, your oil has been dangerously low for awhile.
Thatâs not what you said earlier. ânot dangerousâ and âbarely enough to runâ are mutually exclusive.
As others have pointed out, youâve admitted you donât know much about cars. @Tester knows a hell of a lot about cars, so youâd be better off listening to what he has to say rather than telling him heâs autistic because you donât understand what heâs trying to tell you.
Bottom line, this is a board for adults to help other adults with car problems. Middle school attempts at insulting people arenât viewed kindly around here, and certainly wonât get you better help.
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+1 to both comments!
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Over the years, I have marveled at people who think that they will get better help from healthcare personnel, educators, and others, by insulting them. But, if the OP is dissatisfied with this site, he can demand a full refund of the fee that he paid for posting his inconsistent statements. What is 100% of zero?
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For me, an oil pressure gauge is more useful than a light that comes on when the oil pressure is low.
When I was in elementary school, my Dad explained what the gauges meant. Back in the summer of 1953, my family was on a 300 mile trip in our 1949 Dodge to visit relatives. My dad had filled the gas tank and checked the oil before we left home. About 250.miles into the trip, I noticed that the oil pressure gauge was fluctuating all over the scale. I was riding in the rear seat behind the driver. I pointed it out to my Dad. He immediately pulled off on the shoulder and checked the oil. It was more than two quarts low. Dad and I left my mother and brother in the car and hiked up the road about half a mile to a gas station and Dad bought two quarts of oil, then walked back to the car where he poured in the oil. As a 6th grade student, I got.an allowance of 50¢ a week for doing chores. The week I noticed the fluctuating oil pressure week, I got an extra 25¢ in my allowance for saving the engine.
Back in those days, it wasnât unusual for a carv to burn off some oil in the first couple hundred miles on a road trip.
My dad had been using 30 weight non-detergent oil in the Dodge. His mechanic thought detergent oil was superior to non-detergent oil. When Dad switched to detergent oil, the oil consumption increased dramatically. At that time, the Dodge had 60,000 miles on the odometer. In those days, a car with 60,000 miles was often ready for an engine overhaul.
Itâs wise to get a second opinion from a reliable mechanic whoâs familiar with your model before launching into expensive repairs.
Do you know the evidence for the bad head gasket - ask your mechanic to explain or demonstrate it to you. Do you know the reason for excessive oil consumption? It might be something relatively easily addressed, but also could indicate a worn engine.
As others have said, itâs wise to check oil level on a regular schedule, and keep it above the lower mark. One reason for doing this regularly is to catch and correct abrupt increases in consumption while the level is still in a healthy range. Same for the other fluids.
Car repair is a business transaction. You do not have to be an expert on the inner working of the propulsion system, you just need to do good business practices.
The first good business practice is to get a second opinion. Determine if the first opinion is correct. Do this especially when a mechanic is telling you that you need expensive repairs when you have not been having any symptoms of those âneeded repairsâ.
After getting a second opinion, then it is a good practice to get multiple quotes, just like you would do for any other business transaction. Your first loyalty is to your wallet. Loyalty to a good mechanic has benefits, but that loyalty must be earned.
Back in the old days, most people did not pump their own gas. A service station attendant would operate the gas pumps. While the pump was running, the attendant would check their oil and coolant for them, visually check for low tire pressure and tread wear and wash the windshield.
Now most people pump their own gas so all those other services fall on the owner. You have to not only pump your own gas, you need to also look at your tires for tread wear and tread wear patterns and the appearance of low air pressure and check you own oil and coolant. If there is a window washing station available, then that is on you too.
We cannot verify what you are telling us over the internet. We can only offer advice based on what you say. You got some very good advice here from some very good and respected people. No one meant any offense.
BTW, based on what you have posted, and not being able to actually see the engine, I suspect that you do not have a blown head gasket. I say that because you have not mentioned any coolant loss. If you are having to add coolant or are overheating, then I could be wrong. I also strongly suspect that you do not have a carbon build up problem.
A little black soot on the tail pipe is normal and actually a good sign. Carbon build up would occur in the intake runners and the tops of the valves. You either have to take the engine apart to see this or have a borescope camera to snake down into the intake. You may have some carbon build up on the backside of the throttle body that needs cleaning. That is caused by the EGR system and is normal. You would feel the gas pedal sticking when you step on the gas unless you have an electronic throttle. This is a non scheduled but routine maintenance item.
Carbon build up at 150 k miles is not unusual and in most cases is benign. It can be left alone. It wont do any harm. But again, you would need an eyes on second opinion for this.
You may or may not have an engine oil level light. You can check your owners manual but the quickest way to check is to turn the key to the run position but not start the engine. An oil pressure light will be a red oil lamp icon. An oil level light will be an amber (yellow) oil lamp icon with wavy lines below it. If the yellow light comes on, add oil. If the red light comes on, shut down the engine immediately. If you donât, it will shut itself down permanently in a few seconds/minute.
Edit: with modern cooling systems, you do not need to check the coolant except to maybe look at the coolant level in the overflow bottle. DO NOT remove the radiator cap on a hot engine, it is dangerous. Leave the cooling system to a professional and have that service done according to the schedule in the owners manual. If in doubt, have your mechanic check it out.