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

The first year or two I had my 2010 I remember the cold start shakes. I got it at 163k miles in 2017 and has burned oil since I've bought it. Now 2020 with 183k on it I haven't heard it cold start knock this winter. Supposedly a past owner had Toyota clean the EGR or something. I haven't bothered with it.

I've only done engine oil and filter, cabin filter, engine air filter, front brake pads, flush out brakes, tires. Planning to change out the transmission fluid soon, and put a lift on it. (215/70R15 tires on it right now, oversized)

 

No, the ' B ' line is for Bleed, used when you are refilling the cooling system.

You fill to B, burp the hoses, make sure you're still at B, topping up if necessary, tighten the pressure cap, run the engine in maintenance mode to full thermostat-opening temperature, run it at least seven minutes more while burping hoses, turn it off, allow to cool, and make sure the level ends up no higher than ' FULL '. (If it's below FULL, you then top it back up to FULL.)

The level has to drop by the distance from B down to FULL to confirm the right amount of air got removed.

 

@ChapmanF - When fully heated or after extended freeway driving, will the coolant level rise above the 'FULL' line towards the B line?

 

I've never noticed it doing so. I won't say it couldn't rise slightly. But the B line is there for use in the bleeding procedure.

 

My prius is doing the same but not all the time and also it make such sound (shaking & knocking) very rarely for few seconds, is that normal?
Thanks

 

What’s the miles?

 

418,000 KM, I don’t know I am the 2nd 3rd fifth… or etc owner. I am not using my prius daily I used it once a week or twice a week for short trips like 12 or 10km. My prius behaves newly like this in the morning sometimes when I newly faced with this kind of problem it knocks for 10 or 20 sec after that rarely knocks but a little bit quietly for a very few seconds like 3 or 2 seconds. Today when I woke up in the morning before starting the engine I opened the cooling engine cap And it did very slowly just one knock that’s it. And in other mornings I didn’t open the cooling cap it knock for few seconds then gone I asked from one of my neighbor who has a prius he told me you are not using your prius every day and the weather is getting cold so all the prius behaves the same if not driving daily. But I don’t think so. Today I recorded it’s sound but the building electricity generator was on so you can barely hear the sound of engine knock. But the engine did just one knock after opening and closing the cooling cap. If you can give me your WhatsApp number I will appreciate it sir because in here I should wait for few days to approve my post. In my country there is no hybrid professional mechanic so now I don’t know whats is the issue. If I diagnose the issue then it’s easy to fix. thank you in Advance

 

That’s 261k miles. With your symptoms, and kilometres, its virtually certain to be head gasket failure.

How long have you had it?

 

Approximately 4 months sir. What happened if i just live with this knocking sound?

 

Eventually a bent piston arm, and broken springs in the damper plate between engine and transaxle.

With head gasket failure in the Gen 3’s what typically happens is coolant starts leaking into the cylinders, usually starting with cylinder one (left end cylinder as you stand at front of car facing engine compartment).

the coolant is uncompressible, so engine has to struggle to get affected piston(s) over the top of stroke, also known as top dead centre (TDC).

 

That's not yet what's happening; the engine is just misfiring badly because of the presence of coolant in the cylinder, which is the cause of the awful rattly vibration and noise. It's not enough coolant to stop the piston ... yet.

The problem may progress to the point where the affected piston does encounter incompressible coolant before the top of its stroke. When that happens, it will happen once, and there will be bent engine parts or holes knocked out of the engine block afterward.

That word 'incompressible' really means what it says. The engine will not "struggle to get the affected piston" past that point—something completely different will happen instead.

 

if you are driving short distances or for example you start the engine and switch it off immediately, this seems to be the issue. I have experienced this horrible knock-shake of the engine few times. It wasnt even cold weather. At ANY circumstances DO NOT turn off the power of the engine before it turns off on its own. For example if you are opening garage manually or if you forget something at home, let the engine run. Just hit P, apply hand(leg brake and keep engine running. Sometimes switching off AC speed up auto-kill of the engine. Once the engine switches off on its own, then you can switch your starship off. Dont know technically why, just know its better to wait until the engine makes its own kill-off, only after that switch it off. Hope it helps someone. Last 100000 km no knock no shake. Wishing good luck everyone.

 

What Toyota seems to think happens is during that brief run, the small EGR passages in the manifold can collect water (the stuff makes up 13% of exhaust, and it condenses out). That collected water is in a narrow passage only about an inch below the intake ports, and on the next start it gets snorted into the cylinders, just enough to cause a brief bout of misfiring.

They at one time were pushing a redesigned manifold with those passages apparently reshaped to resist snorting, but it didn't turn out to be a silver bullet; the best advice still seems to be to avoid those brief non-warmup engine runs.

If the symptom isn't happening consistently, but only at times following such a brief non-warmup run, then yeah, that's probably what it is.

 

Yeah those brief non-warmup runs as you wrote…this shakin and knockin sounds occured (in my case) just after that. No matter if you start your car after a while or after one week. If it was switched off while it was cold started and still running, thats definitely not good for this engine design. However, its not an ordinary vehicle so take your time and care of it. Thanks for explaining technical view of the issue, remember my pale green face after hearing that horrible sounds