Engine clatter (fuel knocking)

I owned a 2005 Prius for 4 years and almost 84,000 miles with never any fuel octane or engine clatter problem. I traded the '05 for a new '09 Prius on Jan. 17 '09 (because I can't stand the '10 Prius interior restyling).
Now quite often while accelerating onto a highway, I hear slight engine knock or clattering sound. I am using the exact same brands and grades of gasoline as I did with my '05 Prius. I have taken it in to a local Toyota dealership service department and they could not find the problem or solution.
My gas mileage with the '09 is comparable to the '05 (high 40s) and power seems the same.
Can anyone give me some idea what is going on? It is not my imagination, I definately hear what sounds like low octane engine clatter. I am using 87 octane gas and the dealership said not to upgrade to higher octane as that might make matters worse.
Help, please!

you may not remember from when your 05 was new, but when the vehicle is new the clatter noise when the engine shuts down is much louder and noticeable. It seems to get gentler at around 8,000 - 10,000 miles and practically go away at around 20,000 - 25,000 miles.

This has nothing to do with when the engine shuts down. This happens during acceleration from around say 30 mph to 65 mph like on a highway entrance ramp. I now have over 11,000 miles on my '09

maybe you have a little bit of moisture or water in the fuel tank, I would try dumping in a fuel additive like HEET that removes water and see if that gets rid of it. (remember that water always sinks to the bottom of the tank)

That sounds like a possible cause. I will try that. Thanks

Most gas has alcohol in it, it should say on the pump. If it does, there is no water separation in the tank, the alcohol absorbs it into solution. Heet is just alcohol, methyl I think. Have to be careful with the concentration as too much methyl alcohol eats things readily. Combined with alcohol in the gas it may go over Toyotas spec. I would try 89 octane and see if pinging stops. The valves do make some noise but that is all the time.

I have a 2009 with about 7000 miles, and have not noticed any engine knock.

Try running a tank of 89 octane. If the knocking persists, you could try 91 octane. If it persists, there's either a SERIOUS problem OR you're misdiagnosing the sound.


(remember, the octane rating of gas is a measure of it's resistance to compression ignition, or detonation, which causes pinging)

HI,

Your saying "clatter"? I have never heard that term before. Do you mean pinging? Pinging is very bad. Your car like my 07 has a detonation sensor on the motor that will sense that combustion issue and pull timing to prevent that. You will never hear this car ping. I would imigine if your car is pinging so bad its out of range of the sensor it would throw a check engine code. Any codes?

BY comparison my 07 is very quiet if I floor it. Just smooth engine revving sound. And I run Shell or Mobil or BP 87. You can run a higher octane with no issue. It will just get poor gas mileage and maybe be a little more peppier. Try 93 octane. It will not ping ever on that.

But Pinging on a Prius is very very rare. The car is tuned to run best on low octane. I suspect you have a mechanical issue in the valve train which you only hear under load. Which will be hard to diagnose.

There is a test mode for our car which will enable you to rev the car up while under the hood so you can hear any weird motor sounds.
If interested ask for it.

But what kind and weight of motor oil are you running?

I would immed. change that oil out to Mobil 1 10-30 and use a new oem filter and see if that helps.

I would not add any product to the gas tank as the other poster pointed out.

Because of a possible mechanical defect save a sample of the present motor oil as you may want to send it out for testing which is quite easy and many posters do that here quite regularly.

Good luck.

Check for something loose under the hood. The hood (bonnet) support rod is often the culprit for these sort of rattling noises. Make sure it is snapped into its holder.

Tom

Speaking of the hood support rod.... who in hell designed that thing? I tend to keep my cars a long time.... I still own a 1988 Corolla, for example... and the clip that holds the support rod never lasts the life of a car. No biggie, just a bit of rattle. But this one is attached to the hood, not the body. When that little clip breaks next year or the next, closing the hood is going to be a pain in the ass. What genius decided to put it on upside down like that? Some fancy pants engineer who never drives a car past its first set of tires?

I've noticed that both my 2001 and 2004 had slight ping when going uphill, especially in the summer when using California-formulated gas.

However, when driving the 2004 in high altitude areas in the Mountain West where 85 octane fuel is sold (i.e., Utah, Colorado), I've used that octane and have heard absolutely zero ping.

Now that the 2004 is in Arizona, I don't hear ping. I suppose the gas there is better (compared to CA), not to mention cheaper.

when was the oil last changed?

is it too high or too low?

my 2001 Prius makes a knocking noise from oil not being changed in time, it sludges up and the oil takes a while to get to the top end.

None of those clips have ever broken in a car in my household, despite car ages of 12, 13, 20, and 23 years.

But we've never had a Toyota before either.
[... ducks away fast ...]

Per the advice of "morpheux", I added a bottle of "Heet" to the fuel tank. Almost right away the pinging noise has almost been eliminated, but now I am concerned that I may have too much alcohol concentration as I had only half a tank at the time of dumping in the "Heet". I may head straight to a gas station to fill up. As I said, I never had this problem in the 84,000 miles I put on the '05 Prius.

What fray wrote. If it's pinging see a dealer.

What's the oil level right now?

I have a simple question for the OP. What made you trade an 05 for an 09? You really didn't have too many miles on your 05 which is why I'm curious. I have to agree with you on the '10 interior. I do like the instrumentation, however the center console is a big waste of space. I prefer the open air feeling of my '04. I also love the little gear shift joy stick. I think the main reason for the change was merely to make the car appear more mainstream. It seems to be working.

Did take it to dealers service. They "could not duplicate problem". Oil level is actually above full.

Reasons for trading for new '09 vs. new '10:
1. Liked backup camera on '09...refuse to be forced to pay too much for navigation system to get built in backup camera.
2. Had access to all 4 centrally located cup holders from drivers seat in '09...On '10 the 2 back seat cup holders are now out of reach for front seat occupants and you have to slide the console lid open to get to one of the front cup holders.
3. Front door pockets in '09 were long enough to hold a lot. '10 front door pockets have been shrunk down to merely a bottle holder.
4. '09 Multifunction Display was easy to read with a multitude of large high resolution graphics. '10 MFD is smaller low resolution graphics placed farther away therefore harder to read.
5. Gear shift knob was always out of the way and never accidentally hit on the '09. On the '10 you actually have to reach across the large gear shift knob to reach functional buttons (driving modes) therefore the gearshift knob may be hit quite often.

Bottom line.... These are just some of the reasons you may have noticed a lot of first time '10 Prius owners now registering here on PriusChat and hardly any new '09 registrants. Toyota has deliberately gone to modern "cockpit" styling which is all about flashiness and not practicality. This has resulted in a lot of 1st and 2nd generation Prius owners going to the Toyota showrooms, sitting in the drivers seat of the much anticipated 3rd generation Prius, looking at what has happened to their very practical interior and suddenly getting, like me, very nauseated.

I gather that this has been going on for more than one tank of gas?

Work to eliminate the possibility that you're hearing some loose bit rattling under the hood or inside the cabin. These can be devilishly deceptive.

Over filling the oil is probably not related, but over time it can help foul the throttle plate and cause its own problems. Insist that whoever changes the oil does not overfill it. An easy method is to start with three quarts even (in fact more than that is usually not necessary). Check the level yourself before driving away.