2008 Prius engine clicking sound - 91 Octane gas

I've noticed the same thing on two high mileage 2005's. very common on these cars. I two, would like to know. Like your experience, premium gas made a big difference. Odd for sure

 

Do you use gas from the same station all the time?

If so, switch to another station (Chevron?) and see how their regular octane works....Maybe just be a change in their formulation that your car does not like.\

Here is an interesting article and he gives some possible solutions toward the bottom, such as a new radiator cap.

Ping Elimination

 

Understandable issue. This engine uses solid lifters and unlike hydraulic lifters
See much more wear, so if your not anal about using high quality engine oil
The lifter system will see extraordinary wear. The clicking your hearing is lifter
Slop which ultimately affects engine performance.
Having the oil changed at the dealer is the death knell for this particular motor.

You can fix this noise by inserting shims under the lifter taking up to slop but that's very labor
Intensive. Like I have seen here hundreds of times on posts about clicking
It would be easier to replace the motor.

Best bet for a solid lifter motor is using an oil with a zddp additive.
Most extreme high performance motors use solids as it prevents lifter float
At high rpm. These motors require high quality motor oil with that
Additive. Red line motor oil uses that additive and our motor on there
10-30 version runs extremely quiet. That's what I use. Its a different
Engine on that oil.

 

Along what Ed said above, what oil are you using? Think you wanna be 5w-30 on a older Gen2 and maybe a bit heavier if that does not help. Something like Mobil-1 High Mileage 5W-30 might be a bit heavier or go to the RedLine maybe.

It's hard to tell if it clicking or knocking without hearing it. But sounds like clicking, which is not impacted by fuel octane (use Reg). Knocking is fixed by higher octane, but we are not hearing very many cases where high octane is needed.

Clicking would be more rythmic and mechanical sounding, knocking is more a chatter during acceleration.

 

There is a difference between a clicking sound, and an engine knock/pinging. You first have to decide whether the problem is engine pinging or not. If the symptoms are reduced by using premium fuel, the issue likely is pinging, where there is premature detonation in the combustion chambers due to the fuel/air mixture igniting while the piston is still rising in the combustion chamber. Premium fuel does not ignite as easily, so the pinging is reduced.

If the issue is pinging, then it is possible that the pistons have built up carbon deposits which result in higher engine compression, thus causing pinging when regular fuel is used. So, if you want the sound to go away, continue to use premium fuel.

No, it is not likely the problem is in the catalytic converter if the symptoms are reduced by using premium fuel.

 

Well, I am yet sure you have knocking, as high octane should stop it.
But you might be interested in the recent posts by @chogan2 where he tried heavy doses of Chevron Techron, with apparent success.

 

My 08 is bad for this (480,000Km)

If its the same noise that I think it is, it has nothing to do with lifters Patrick is correct Its pre ignition aka detonation or "ping" caused by carbon build up on the piston tops, good fuel ignites later so it shifts the "spark" away from the areas of most carbon.

I find it to be much worse on hills if the battery has low soc as the load on the ice is much greater when the battery is low, if I hit a hill with the battery in the green it pings much less than if the battery is low.

the better the fuel the less it pings, if I buy ultra premium 98oct fuel the ping almost goes away completely, if I buy 91 it pings so bad you think your engines going to self destruct

 

Could the knock sensor be bad?

 

Higher octane not so much "better" fuel, just harder to ignite, so more suitable in higher compression engines. Or older, regular compression engines with lots of carbon build-up.

 

Yeah sorry I didn't want to go off on a rant about octane ratings. better fuel = more octane.

requires more combustion to ignite = shifts the explosion slightly away from the carbon build up

another thing i noticed my 08 pings way worse on non ethanol fuels than it does on 10% ethanol of the same ron rating

 

Not really surprising seeing as in NZ, Aust, UK and EU the Gen II is supposed to run on 95 RON minimum (89-90 AKI in the USA).

I second the comment of your illogical emotive language that low RON equals bad and higher RON equals good. RON rating has only to do with using the correct rating for which the engine is designed. You can use higher octane rating without problem (except a lighter wallet), but you can't (or at least shouldn't) use a lower octane rating.

 

I see posts on here suggested prius was designed to run on low grade 89 gasoline

But I never realised, or even cared to notice that US fuel is metered on the AKI system rather than RON, thanks very much for the tip Dolj .. does this mean US 89 AKI is around the same bang as AU/NZ 95 RON ?

using "too higher" rating octane can cause overheating, been known to blow head gaskets be careful with that

 

In the US, all Priuses are rated for 87 AKI, which is roughly equivalent to 91 RON, for what it's worth.

And I had always seen that it was 91 AKI that was closest to 95 RON. (Note that in many parts of the US (west coast, high altitude, some major cities elsewhere), 91 AKI is the most you can get.)

 

@bhtooefr has it correct re: octane...It's a little hard to imagine a lot of carbon on a Ca. clean gasoline at 100K miles, but I suppose it is possible as @chogan2 had a similar issue here in NoVA where we also have RFG gaso.

 

I would have the knock sensor inspected/replaced it could be failing.

 

Per our manuals in the USA it states that we can use 87 or higher octane, so if higher octane would harm the engine, I would think Toyota would state otherwise. I only use 91 in my Prius.