Most of you may not hear your engine knocking sounds at low rpm, gradual acceleration at about 15 to 20 mph, because you're not looking for it. I often heard this ugly knocking sounds because I drive uber in chicago and when the windows are rolled down and you are going through a narrow alley with parked cars on both sides, you can hear this ugly knocking sounds very easily. This sound bothered me a lot and I have been trying to find a cure for it for over a year now. I asked my mechanic to do this, and this and that without any avail. I tried putting in a bunch of expensive fuel injector cleaners. None of that even helped noticeably. 😕

Well, I finally got it to stop knocking. I'm posting this because if you own a used HS, this could be a common problem. Anyway just in case, i asked my mechanic to replace all the spark plugs (been only 55k on the last set up spark plugs), and that actually stopped the knocking sounds. It also helped improve the gas mileage by 3 to 5 mpg. I'm going to change my plugs every 50k now. The cost of plugs will easily cover your cost of wasted gas. For iridium plugs, this is kind of too often (50k replacement), but I think because of the 2.5L toyota four cylinder engine piston ring problem fouling up the plugs, it might be necessary to replace it often. Maybe it's not even all four spark plugs... maybe it is just that one cylinder with the bad piston ring 🤔

 

It's all four cylinders equally. I guess i'm going to clean the plugs and regap.Maybe.. anytime it starts knocking again..

AI says :
"There is no specific cylinder that burns the most oil in a 2AZ-FE engine; it is a systemic issue affecting all cylinders. The excessive oil consumption is caused by faulty piston rings, a known problem for this engine, especially in models produced between 2006 and 2014. Therefore, the oil burning isn't localized to a single cylinder, but rather to a design flaw that allows oil to enter the combustion chamber of all cylinders."

 

It is more difficult to clean and gap Iridium plugs than the old school copper plugs. Given the low cost of 4 plugs if doing it yourself, just buy a set of plugs.
The new Ruthenium (sp) plugs claim better life etc for a few dollars more and are what I installed on my HS a few months ago. It runs smoother and Mileage did go up a little.

 

i've never heard of ruthenium spark plugs. 😳 but, I guess I will try that next! At 186,000 miles, my HS burns 🔥 2 qts every 5k oil change. I'm guessing that this (oil seeping past the defective piston rings) is the cause of the plugs getting fouled so quickly! 🤷 😔

 

That may be the source. Keep in mind that 40 - 50 years ago it was considered normal for a vehicle to burn a quart of oil about every thousand miles!
New vehicles have much tighter tolerances and better materials that reduce oil burning, increase gas mileage and engine durability, plus the oil is much better now.