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Popcorn Popping sound under the hood

At 50 MPH and above, a popcorn popping sound occurs - varying fast and slow - only began after car was serviced. Can’t find the source. Checked since it started and still nothing found - but new thermostat was installed, new gauge panel (due to car appearing to overheat but it was a faulty gauge), new wiper arms installed (thought they were the cause), running board rubber re-attached (thought it was flapping) - none of these were the cause because it is still occurring. Help!

Exactly what was done during the servicing visit? Was a new timing belt included?
And what kind of Chevy is it? Make, model, engine, & tranny?
How many miles does it have on it?
And do you have a lit Check engine Light?

It sounds like something is hitting something else. It’s important to immediately check the timing belt condition and all the drive belts for anything unusual. If they start fraying, they can make this kind of noise. If so, you want to fix it straight away, as the fraying can get worse and do serious damage. Hopefully this turns out to be easy to fix.

Could this be bits of the serpentine belt? I have had this issue. But it did not last long before the belt went all the way.

It is a 2004 Chevrolet SSR convertible truck. 29,800 miles. No new timing belt was installed at the service - only oil change. Chevy dealer kept it for over a week when I took it back without figuring out the problem. There was no check engine light and no gauge problems the first day I heard the sound after the service. The next day the temperature gauge was a little hot and I took it back for that as well as the popcorn sound. Their ideas were: water boiling due to overheating creating popcorn sound, wiper arms with loose fittings causing sound and/or rubber on running board loose and flapping. They looked all around under the hood - will have to ask if they checked the serpentine belt - but found nothing. Today - really bad popcorn sound when first driving then it seemed to go away. Probably not good. Anyway - result of week at dealer was $2,000.00 in other parts & labor - the new instrument panel for the faulty temperature gauge - which apparently can’t be purchased separately; a new thermostat installed which was apparently not needed, new wiper arms and rubber gluing.
Thanks for all the suggestions!

When you press the gas sometimes does it bog down and not give you any power? I had this issue before on my car. It was the air intake chip, dunno if thats the real name of the part but its the thing that regulates how much air vs gas gets used. I would press the gas down at times and I would just hear popcorn sounds and get no power from the gas and then it would kick in alluvasudden.

You need a new shop…desperately. Their ideas are (1) totally devoid of any sane analysis, and (2) nutty. And any shop that cannot tell water boiling from a flapping windshield wiper or a loose and flapping running board should be avaoided at all cost.

There are a number of possible causes for the sound plus the overheating. And they can and should be properly diagnosed.

It sounds like the thermostat was either faulty or installed backwards but you say they installed another one and the problem still occurred? Did I understand that correctly?

Yes, by all means try another shop. And it is difficult to interpret what “popcorn sound” is. My first guess is pre-ignition and overheating can cause that problem. But the most common description of pre-ignition compares the sound to rattling a tin can full of nuts and bolts or gravel while accelerating.

I too am having a hard time with the "popcorn sound, but all I can think of is ,isfiring coming back through the intake manifold, which is why I wondered if it had a timing belt changed. Knowing now that it was only brought in for and oil change…how can a shop screw up an oil change in a way that causes popcorn sounds??? All I can imagine is that they knocked a vacuum line off. But from everything I’ve read so far, they were totally incompetant and anything is possible.

Get this to a new shop ASAP. This type of misfiring can possibly be destructive if left unresolved.

Does this car have electric fans, or a clutch fan?? Could the issue be there?? Could the fan be hitting something??

If you rev the motor while not at speed can you hear the sound or is it just under load?

Yesterday my truck pushed out a spark plug coil… 99 Ford f-150. The rubber that goes over the coil and the spark plug split and is causing a popcorn sound. Not a slapping sound like a belt hitting something. Don’t know if yours sounds like mine, but what i did until I get my new coils tomorrow was put electrical tape to hold the coil together and it reduced the noise. It didn’t stop it completely but it helped. The igniter for the spark plug was escaping. I wouldn’t recommend using this as a solution but just thought I’d share what I’ve experienced with this sound so far. Tomorrow I’ll update after I change the coils.

The coil is not designed to hold the spark plug in the cylinder head. Take a look at the spark plug threads in the cylinder head, they must be damaged. There are spark plug hole thread repair kits available for these engines.

Yeah, we thought the spark plug was shot out, but it was still in place. Isn’t loose. The parts came in and we are going to replace all the sparkplugs and possibly rethread. The coils are 20 years old and the kid that I bought the truck from didn’t take care of it. So we’re slowly fixing it up. We shall see how it goes today.