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Accelerator sound when heat gauge is at half

(Please excuse me for my English if you find any mistakes) I live in Saudi Arabia, and I enjoy listening to your show “car talk” By listening to your show, I have concluded that both of you are genius. It is not possible for me to call in your show, so I thought to write my question here. My car’s heat gauge reaches to half and then stays there for the rest of the ride. When it reaches at/close to half, only then I hear a knocking sound while accelerating. However, if I press the accelerator only slightly OR full way down, then sound goes away. Any ideas what is wrong with my vehicle (It has run 400000 miles)?

Try a better octane gasoline 1st stab at the cat.

What kind of vehicle and what year? Also, this forum is not visited or commented on by the same people that do the show, but instead by fans and other random people. I barely listen to the show personally but like this forum.

It does sound like you need to use higher octane gas. Also, at 400,000 miles, the engine may have a lot of carbon in the cylinders. Carbon heats up and can ignite the gasoline charge before the spark plug fires, causing the sound you’re hearing. Continual “spark knock” can damage your engine. It would probably be a good idea to run several bottles of a fuel system cleaner through your vehicle for the next few fill ups, preferably “Techron” if you can get it there.

Thank you “Barkydog” and especially “oblivion”. I have Dodge grand caravan 2006. I am using 91 octane fuel, I am not sure if I can use higher octane i.e. 95 in my car? I could not understand the term “fuel system cleaner”. Are you referring to add this “Techron” along with fuel (Patrol) in the fuel tank OR is it some engine oil?

Here I have two types of fuel available i.e. 91 octane and 95 octane. The manufacturer recommendation is 87 octane. I am using 91 octane now, will using 95 help in this matter?