Loud engine sound at start-up

Welcome to the engine knock club.... not a very exclusive club. Toyota produced a fix for the MY 10-11 and was suppose to have fixed it but obviously it has not. No worries. Just report it to your dealer and make sure they write it up... toyota needs to know it is not fixed.
Some things to watch for, make sure if you move the car when cold that it completes its warm-up cycle before shutting it down. The issue seems to be with condensation building up in the intake manifold and being sucked in when starting up.
Welcome aboard by the way!

 

Only happens shortly after partial solar eclipses! Will never happen at a Toyota service department, regardless of sun/moon configuration. Been there, done that. Not to worry! In this case, they (Gen III Prius) may actually all do that!

Be reassured that Toyota feverishly continues to work on solving this little annoyance. I heard that the fix may have been found and I think Toyota calls it the 2015 Prius. Stay tuned!

 

Our Prius (2010) has had the knocking problem twice in three years. Both times it was after sitting for a long period of time (several months). I've read that it is moisture that condenses in the intake manifold when the vehicle is parked at temperatures below 40 degrees. There is a Toyota bulletin about the problem and some of those with documented problems can have it repaired, which means replacing the manifold and a few other parts. Since ours only has a problem after being parked for several months over the winter, I doubt that it will ever be officially documented, but I did have the service people at the Toyota dealer write a description of the problem on our last service receipt.

 

I've heard of a noise after the wrong oil is used. It would be seemingly harmless to use 5 -20 instead of 0 -20 but it can cause an engine noise when the car is cold. The wrong weight oil causes something that sounds like a valve clatter or timing chain noise. Did the op say it was just after oil change that the noise started? Maybe get the oil changed again and see if it helps.

 

Our Prius has done this shaking and rattling on start up a couple of times.... also after sitting parked a while. Service department wanted our car overnight to see if they could duplicate the problem. Of course, it didn't do it for them.

The second time it happened we called the service department, and this time they said it' was nothing harmful. Seems to be a pretty wild shake and not so nice noise, for something that's supposed to be benign!

 

I've seen the shaking and rattling numerous times with gen 3 prius I was starting at work. I assumed it was from starting with a low 12v batty but I have no evidence to back that up. It never seems to cause or indicate any issue.

 

The few times it has happened to my car, I had shut the car off right after the engine had powered on (for example, I was moving the car from the curbside to the driveway (to wash it) and the engine kicked on just as I was powering down the car). When repowering up the car (later) the engine knock would occur. However, that said, the last time I inadvertenly shut the car down too quickly, it didn't do the knock.

 

I powered up my car last week to check my HV battery level and my motor just about started but I caught it before it started but after the fuel pump prime cycle completed. So obviously there would be no moisture in my intake but it did get a shot of fuel before I powered it down. I was about to do a force charge as the car has to sit until June. So a minute later I powered it back up and it did the fuel pump prime cycle again before starting and it got just a couple seconds of the rattle and it quieted down to normal all by itself. I would think it is an overly rich condition rather than moisture since my garage is heated and has a dehumidifier in it to keep things dry. My car was not run since a couple months ago when it got a 100 mile drive on it. My 14v battery was at 13.xx volts since I had my maintainer on it earlier that day. My car has never had the noise before but I have always let it run it's full warmup cycle by itself except this one time it got the fuel prime cycle twice in a row. Even my SUV will cough on startup if I give it two consecutive prime cycles which I have done before. My Prius is an early 2012 build date. I should note that my car powered up and started perfect last summer after sitting for 8 months straight in my garage so I would not think it is a issue of the car sitting for a long time.

Mike

Mobile on my SGH-i717

 

I had the same problem yesterday, Dec. 19, 2013 .... started the car (Prius IV 2011 - original owner) and the engine? made the loudest noise ever. Quickly turned off the car, waited and restarted - same loud ratting metal noise except not quite as loud. turned off the car again, restarted, same noise only considerably softer. Repeated turn off and turn on several more time until the sound was gone. Took my Prius to the dealership and they said the noise was due to the car sitting all night and the oil not be disbursed yet. This made no sense to me and told the fellow. No further help from him. Repeated my story to another person at the inside counter and received polite listening but no help. This incredibly loud noise does not seem good to me and I'd like some help here. Anybody ?

 

See Post #2 Spiderman

 

I have had this problem several times with my 10 Prius. In addition to not shutting the ICE down untill fully warm, I have found that starting in very cold weather or after being parked for several weeks or longer, start the engine and immediatly shift to N. This relieves the cold misfiring engine of the added load of immediatly trying to recharge / warm the traction and 12V battery. After 15-30 seconds or so of running without load, the engine will smooth out. At this time, shift to D then to park, The now smooth running ICE will again shoulder the normal battery charging duty.

 

Just this Saturday my friend called me in a panic, stating that his 2012 Prius had made a horrific noise upon cold start. I had to assure him that it was nothing that would cause any damage and that it was an anomaly with the Prius ICE. I also told him to take it to the dealer as a precautionary measure and if nothing else to have it put on the record. So, it seems that Toyota even has this problem in Prius vehicles built beyond 2010.

 

I have it on mine with under 3k miles. It first did it at about 600 miles.

 

You need to allow the ICE to complete the engine warm up before turning it off. It must often happens when moving the car in the driveway from spot to another and switching off the car before it shuts off.

 

Nope. Has no effect on when it happens or how often. My 2010 Prius did the same thing, even after the TSB was performed to supposedly fix it. It's a random occurrence that may well happen when moving the car and not letting the ICE completely warm. But it also happened the morning after a 500+ mile trip. There's no rhyme or reason to it.

 

Maybe cheap gas?

 

E0 89 octane Exxon. And it ain't cheap.

 

Exxon is top tier, but could it have been a bad batch of gas, trust worthy dealer, I try to use Chevron only, as the manufactures use Chevron for their vehicle testing.