Crazy sound upon ICE startup

Sounds like a stuck valve. Have someone look at the camshaft for signs of impact to find the culprit, and to see if somehow the oil isn't getting there.

I leave the climate system (heater) on on cold weather, so the ICE comes on when I first power up. Better to have it start when at rest than while underway, in case there's a problem.

 

do you have a habit of starting the ice and shutting it off before it has completed the warm up phase and shut off on its own?

 

How many miles on it?

There's a number of theories, and other 3rd gen owners are reporting similar noise. As @bisco alluded: it seems to happen a lot if the car is cold started and quickly shut down. At the next start up the knocking occurs. I've had it happen once, in just this scenario. Shutting down and restarting: the sound was gone.

Toyota's been saying it's the intake manifold design, for some time now, but IIRC some owners have had intake manifold replacement but continue to have the problem?

My suspicion is that it's related to the EGR system clogging, but just a hunch.

 

correct. two things: replacement manifolds have not solved the problem. have they reduced it? we don't know.
later gen 3 came with the updated manifolds, but still have the issue.again, we cannot quantify.
the only guaranteed solution is owner discipline.

 

Me neither. How long till it shuts engine off by itself, under 5 minutes? I keep thinking this phenomena makes the 3rd gen Prius like a finicky, special needs child: special care and instructions needed.

You have very low miles still, and with the plug-in, even less engine running, so likely not the EGR. This is a mystery Toyota should solve.

 

you probably don't have to let it idle until it shuts off, but we have no metrics. you will have to experiment by timing each operation, and adding more time before shutting down, until the start bang stops happening.

 

excellent. no other reason to let it warm up then.

 

using grill blocking?

 

most put styro pipe insulation between the grille ribs. i use it, but it's like tyre pressures, no proof it does anything, but lots of conjecture.

 

The Gen 4 has automatic grille shutters so Toyota must think it does some good.

 

Race cars do it too for the aerodynamics, so ...

 

Interesting. I've owned two Gen III Prius: A 2010 and a 2012 Plug-in. The 2010 did it often, but I don't think my PiP has ever done this.

 

Happened to my PiP yesterday for the very first time. It was about 10°F out and car had just cold-soaked in it for 8+ hours. Engine started immediately on power-up and made this sound until the coolant made it to about 15° (maybe 15-20 seconds) and then it sounded like normal. I'll keep an eye on it, there are more super-cold days this week where the engine will fire up when I leave work after that cold-soak.