New Prius owner

How many miles on the car?

It sounds like someone sold you a car with a bad head gasket. Very common problem on the Gen 3 engine. Did you buy it privately or from a dealer?

Search on this Gen 3 forum about bad head gasket, and start reading the couple of hundred threads that you will find.

 

With the info provided, most likely a
Head gasket replacement is needed. Wait Long enough and you’ll have a busted rod thru the block in the middle of the highway putting people lives in danger. Dump some leak stop in it and post the vehicle on carvana, shift or carmax.

 

If he sells it, he just needs to sell it in the afternoon. The car won't act up unless the engine is cold.....for now

 

You just bought it, but it drove like a new car when you bought it???

 

I bought an almost new 2012 Prius Touring (upper trim with 17" rims) in 2014. I have driven mine for 10 years now.

About 5 years in, I started noticing the car engine startup rough and shake on startup. Apparently this is common problem with the gen 3 Prius. The rough startup would happen to me once every couple of months, but I just ignored it and continued driving. Its been more than 5 years since and 230k km. I just replaced my spark plugs last month and it just shook once about 2 weeks ago. I guess it really depends what the cause of the shaking is.

After looking around forums, I believe the below are the causes:

There is an exhaust recirculation system (EGR) which passes hot burnt gas fumes from the engine back into the engine so that it warms up faster for better fuel economy. These fumes contain black carbon which overtime can clog up the passage way. This clog can cause engine shaking as it struggles push exhaust fumes.
- there is an magnetic EGR valve that opens and closes to let fumes into the engine and operates on engine startup. Sometimes this is stuck with carbon.
- there is an EGR cooler and extending pipe that exchanges heat between exhaust and coolant. Sometimes this is stuck due to carbon buildup.
- there is an intake manifold that feeds the engine with air. Sometimes the small inlet holes are clogged with carbon. The 2012 Prius should have the updated manifold to help prevent shaking. There is a Toyota TSB about this.

Some have checked their spark plugs and fuel injectors. There is also updated hotter spark plugs to ensure that engine hotter. I bought my spark plugs in 2014 and just put them in so I am still using the older ones.

Another major cause is the head gasket in which coolant is seeping slowing into the engine which is causing the misfire. A lot of people seem to be pointing to this as the 3rd gen Prius is now over 200k or 300k. I wouldn't jump to conclusions without a proper test.

I bought a Prius as I commute quite far for work. I drive over 130km at least once a week in one trip. Long trips help prevent any EGR clogs as I would thoroughly warm up the engine. My engine shaking happens once very few months and it always happens on startup. If your engine shakes on startup too frequently, it can be a serious problem.

 

how many miles on her?

keep a frequent eye on the coolant level and oil level.

could be an egr problem, or seller might have dumped in some leak stop, which doesn't last, and can eventually clog the radiator.