Loud engine sound at start-up

Register your car on the
Toyota Owners Official Web Site: Service Coupons, Owner's Manuals, Service Scheduling And More
website.
Then check your car under the "Resources" dropdown menu, "Safety Recalls and Service Campaigns". There was an issue with some Gen III Prius needing an intake manifold replacement that caused this kind of issue. It is addressed in T-SB-0204-11 if you want to search some more here on Prius Chat.
You may find this or some other free recalls or Limited Service Campaigns for your car as well on the Toyota Owners Site.

 

I don't use any high priced gas. IMO it's a waste of money. I've put Exxon / Mobil in my a few times when it was necessary and it doesn't make any difference in performance or mileage.

 

It will keep your engine cleaner. It pays off in the long run.

 

The issue has nothing to do with previously running an engine. See my post above for when it happened on my car. Sitting for a while is not an issue either. Low octane gas is not the issue because high octane fuel still won't prevent the issue. It appears to be software related in how the variable valve timing is changed upon start up. I know for sure that you do not want to allow the fuel pump prime cycle to happen twice in a row without allowing the motor to start and warm up. It acts like a overly rich engine stumble like you could do with a old school injected motor.

Mike

 

One thing is for sure... Toyota hasn't figured it out yet. The Atkinson Cycle engine has very complicated valve timing characteristics that are the cause and effect of this combustion anomaly. The most complicated challenge is convincing owners that this issue is the nature of the beast. It a hiccup. Toyota needs to release a TSB that suggests that you take a swallow of water and hold your breath. )

 

WEOH,

Have you confirmed that better fuel does not work?
I ask because I want to update my suggestions.

I have been able to avoid the issue during the winter months by using the higher octanes in my area.
Tho, I also treat my tank with HEET.

Originally, I did experience the issue 2 times the first winter and it has not come back.
I'm still on the original manifold with 45K miles.

SIDE NOTE:

I noticed from reading PC, there are two kinds of knocks.

1.) Loud pinging but smooth. Seen in Youtube videos. ( I got this one)
2.) Loud rattling like something was hitting inside. Metal noise hitting with shaking.

I think it's the same problem but there are different degrees of severity.
My sound did not alarm me and I blamed the winter, brutal cold at the time.

thanks.

 

I had 105 octane in my tank (affordable fuel in my area ) when it did it but then again it lasted only a couple seconds at the most. But,,, moments earlier I only did the fuel pump prime cycle as I was booting up the car to see how much my HV battery was charged to see if I needed to do a force charge. Since it was down a bar further than I wanted, for leaving my car 6+ months in storage, I opted to force charge which meant I had to fire up the motor. Since I knew it went thru 2 prime cycles, I kinda expected it to at least be way rich running at first, and it did a ~2 second stumble making that loud valve train clatter that everyone hears. Previously the car was driven on a ~100 mile trip and driven into my garage as normal and powered off as normal. My opinion is it is a software issue in how whatever computer is running the variable valve timing. I wonder if other vehicles with the Atkinson Cycle motor have kind of odd start up issues on occasion? I understand the Prius motor is run as a Atkinson Cycle motor by the computer running the variable valve timing rather than a fixed hardware method. I haven't studied the Atkinson Cycle motor in depth, but I suspect it is done with the cam's in a motor without variable valve timing. If you have played with motors where you have adjusted cam centerline and worked with custom grinds you know that you can change the way a motor runs/performs dramatically. You can design a cam for fuel mileage, torque output or HP output and the centerline determines where the powerband is. You may already know that stuff. I am an old school gearhead so I have been doing that old school way as we did not have variable valve timing motors back then About that 105 octane fuel, it is a very very controversial topic on this forum and I gave up debating it a while back. I can explain in a Private Message so this thread doesn't go down the shitter in a hurry. Lets just say it burns very clean and runs flawless in the Prius

Mike

 

This just happened yesterday morning in my '13 PiP for the first time - just about 5k on it. It was remarkably violent. As soon as I shifted out of park it settled down. About to get the first service so I'll make sure it's documented.

 

Mine continues to make the racket when starting. I don't use the engine very often as I'm able to drive in EV most of the time. It happened yesterday when I ran out of EV running at about 40mph. It wasn't violent but definitely noticeable. It knocks on every startup. I'm using E0 and put a can of Heet in it a couple of months ago to no avail.

 

Doesn't really matter that you don't use the ICE often- as long as you let it complete it's warm-up cycle before shutting it down you shouldn't get cold start knock. If you're getting it "on every startup" there is something very wrong with your 2013 PIP. Maybe even a lemon law candidate if Toyota can't fix it. I've had my 2012 PIP since Oct 2012 and have experienced the cold start knock exactly one time. That was because I moved the PIP out the driveway and back to clear snow with a depleted EV charge so the ICE started and ran for only 2 min or so- the next morning I got the cold start knock.... but that's only one time in almost a year and a half of ownership.

 

It may be that I don't let it get warm enough. When it starts it's usually only on for 15-20 minutes. SG shows between 170-180F but the length of time running may have more to do with the issue. I've only got 3000 miles on it and most of them are from a trip to FL and the initial pick up from NJ.

 

Come to think of it, I believe the night before I experienced this, I had driven the car home on EV until the last 1/4 mile or so when the ICE had to kick in so that could well be it. I've cut the warmup cycle short plenty of times before though as it's common that my around town trips are too short for it to complete.

 

15-20 min and 170-180 F is long enough to complete the warm up cycle.
To be sure- if you put the PIP in Park- does the ICE shut down? If it does- you have completed the warm up cycle and should not have cold start knock.

 

The ICE shuts down often after reaching 130°F. I can coast along as always with the engine off. I just thought by not running the engine enough, it causes the knock...on every cold start...even though it's not very frequently started.

 

130°F? seems like you're in "ECO" mode. Maybe try running in normal mode at the end of your trips and see if you still get the cold start knock...

 

I keep it in ECO all the time. I'll switch to normal for a while and see how it works. I'm also not charging for a while to force hybrid mode.

The knocking has been present since I got the car. It's never been violent but just a quick loud valve tapping noise that lasts for about 10 seconds or less. As you pointed out earlier, it may be defective and needs Toyota to address it. There's no codes being thrown or stored but my Gen III didn't have any codes either.

 

Mine was definitely not valve tick. It shook the car substantially and totally freaked my wife out.

 

Warm up warm up, its as simple as that. With the cold winter most of the country is experiencing this year it may have something to do with it, you may want to look into an engine block heater. They are sold in Canada..

 

+1
The one and only time it happened to me- it was loud, shook the car and was pretty scary.

 

I too have experienced this "issue". Unfortunately, it happened while parked in a parking ramp on a day where the temp was 20 below with a strong north wind.
Took my 2013 in to the local Toyota dealer yesterday to "look" at it. Of course all is well but I wanted it documented and I want this to cost Toyota so they will do further research. If all 2010-2014 owners took their car in complaining about this, I believe we would see more action by Toyota.
The dealer was telling me that they have experienced this issue with cars on the lot too, but, there is no resolution as yet as the symptom is so brief. I just wonder what long term effects this has caused or will cause to a very expensive engine.

While I had it in they also flashed the ECM for the recall.
This is a great group!! I just ordered the Cusco strut tower brace yesterday. Can't wait to install it.