Very scary noisy vibration on a cold start...occasionally

yes, many. it's just poor design by toyota.

read through the egr threads, and check @NutzAboutBolts youtube channel.

pray that you're ahead of a blown head gasket

 

If it sounds like the beginning of this video, happens at initial cold start occasionally, it is likely the initial symptoms of a head gasket leak. Increasingly common on 2010-2015 Prius engines.

The leak may be small and short enough not to dramatically drop the coolant level although coolant will be consumed. There are various tests to confirm.

 

I had a 2016 Prius and there were no problems for 4 years and no problems for the 6 months on my new 2020 AWDe Prius.

JeffD

 

The initial leaks are usually slow enough where it burns off without misfires once you are running well. After it cools off for hours the coolant has time to fill the cylinder and cause a misfire until it is pumped out of the cylinder. If you are unlucky enough to be at a low cylinder position full of coolant on the compression stroke, parts bend. Which is when things can get seriously beyond a headgasket repair.

They fixed most of the issues by the fourth gen. Toyota even acknowledged and warranty repaired some piston ring problems if under the powertrain warranty.

Were they saying they would fix a head gasket under the emissions warranty if codes occurred? Typical head gasket codes are usually misfires of the plugs.

 

there are members in here that would scold you for pulling a move like that heh. Intentionally selling a vehicle that’s on its way out and an innocent buyer / dealership thinking they scored a good deal on it. Oh well, one man junk is another man’s treasure.

 

Cautionary tale, 100k clean of EGR and intake manifold may be too late?
Every 50k better?

 

Check the most recent dealership entry by running the VIN at : Track Your Service Records with Your Toyota Owners Account

Is the coolant level in the reservoir going down at all, the liquid level is around the plastic seam when cool or the hot line when hot.

 

I don't recall 3rd gen has a "hot line". Top mark is just slightly above the horizontal seam, hard to see. Put a strip of masking tape on reservoir, mark coolant level with a Sharpie (say when cold), then monitor.

Always recheck under same conditions, preferably level car and engine cold.

 

Looks like the hot line is labeled ' B ' for boiling?

Example here :

 

I'll have to check. It's the top line and says "FULL" anyway.

 

or non existant. i wouldn't rush to get rid of it.

 

I have exactly the same problem. Once in a long while my Prius shakes/rumbles on startup. I find it more likely happens when:
1) Startup in colder weather
2) Startup after driving the car for short distances and leaving it off for more than a day.
3) Startup problems are less likely after driving car for long trips so that the engine gets hot.

It seems to be the #1 problem on PriusChat for the gen 3 Prius. There are range of possibilities including:
1) Clogged EGR or pipe
2) Clogged intake manifold
3) Starting signs of headgasket failure

Since the startup problems don't happen often, I have simply done nothing about it. There will be a day I will have to do something about it. Toyota is known for reliability, but this is a disappointment.

Prior to COVID-19, I used to commute to work and drove the car 1-2 hours a day. The startup shaking never happened on a work day. It also never happens if you restart the car immediately after a long drive. I would say the car is not designed to be driven less.

 

Watch the coolant level. A normal engine won't lose a drop. Head gasket failures on these cars start small and act just as you describe. Until the day it quits and the hybrid failure light comes up. Even then it may run but with the shaking happening more often and eventually with white steam coming out of the exhaust. Then its either death by overheating or a rod breaks. It is disappointing and even more so when fanboys here downplay it because their car is fine. It is especially sad when someone has just paid good money for a 2010-14 only to see symptoms shortly after the seller's can of block sealer has worn off.

 

100% is LESS able to do its cooling job If I recall correctly. Not recommended.

You’re concentrating on symptoms, not the cause. My 2 cents: I’d rather deal with failing head gasket and clean the EGR/intake, than a hydrolocked door stop. But it’s your nickel, lol.