Engine clatter (fuel knocking)

[jyoungprius]

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!

[morpheusx]

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.

[jyoungprius]

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

Originally Posted by morpheusx

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.

[morpheusx]

Originally Posted by jyoungprius

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)

[jyoungprius]

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

[Mr.Vanvandenburg]

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.

[yardman 49]

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

[Frayadjacent]

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)

[edthefox5]

Originally Posted by jyoungprius

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!

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.

[qbee42]

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