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2008 Corolla- new engine?

I have a 2008 Corolla 5 speed w/ 23,000 miles. Started one morning after sitting for 1 week and the engine made a loud clicking noise (like tappets clacking but REAL loud, or like a playing card pinned to the spokes of your bike). Could not tell exactly where coming from in the engine, shut off, towed to dealer (under warranty). Dealer 1st said needs new engine, then “performed a top end engine clean w/ chemicals”, and the noise was gone. Dealer said problem possibly carbon build-up from cheap gas (not, I use Chevron or Shell), or m/b from 1 bad batch of gas. What caused noise, and if it was carbon, why after 23,000 miles? Future concerns? Thanks in advance.

It’s entirely possible to have a carbon or sludge problem in 23k miles depending on oil change or driving habits.
What oil change intervals do you use; both mileage and time-wise?

It’s not likely bad gas at all and they’re simply throwing that out as a wild guess.

Just offhand, my guess would that it could have been one of the following, and any of them could be related to oil sludging due to extended change intervals.
If the engine uses hydraulic valve lash adjusters, possibly a sticking adjuster.
Cam chain rattle due to sticking or sludged chain tensioner (oil press. operated).
Worst of all, rod bearing rattle due to a sludged up oil pickup.

It is also possible to have carbon buildup in the intake, a small piece come loose, and then bounce around in the cylinder. When this happens the piece of carbon will instantly start glowing red hot and will cause severe detonation.
The sound can make you think the engine is gone for sure, but no harm, no foul.

At this point I would not worry about it unless it happens again. (And make sure you have all of this documented; just in case. You should have been given copies of paperwork on the current episode spelling out the complaint and what was done.)
Hope some of that helps anyway.

Oil changed religiously at 5K, always use premium oil. I have had the car 1 year, so changed 4 times at regular time intervals. Forgot to say that I checked the oil at the time of the noise, it was at the full line and clean looking. As far as driving, I always shift between 2K and 3K, and try not to ever lug the engine. The car was driven every day until we left town for a week, thus the week long delay. Thanks again.

5k miles/3 month intervals are fine and sludge should not be an issue.

I’m inclinded to suspect that the information you’re getting is from the service manager. That job has two criteria: lack of mechanical knowledge and ability to BS. I think he was exhibiting both of these traits.

Cheap gas does not cause carbon buildup. And I seriously doubt of that car had carbon buildup. Unless it’s been running really poorly, really rich, with horrible mileage. Carbon is a product of too many hydrocarbon molecules with too few oxygen atoms to bond to…too much gas, too little oxygen.

The “top end cleaning with chemicals” I’d suspect was probably an additive used to clear sticky tappets. Although sticky tappets in a properly maintained Corolla engine with only 23K miles would be unusual. That engine has no severe oil stresses like a turbocharged car might.

What I suspect actually happened is that they dealt with a sticky tappet by using an additove. It’s also possible that the technician corrected something simple and the service manager didn’t know what and just made up an answer for you, as they often do. The clicking noise could have been as simple as a loose plastic snorkle or air box that needed tightening.

I truely do not think you have any need to worry. However it’s always prudent to get everything detailed on the shop orders and keep your copy.

You could have had an oil filter with a leaky drain-back valve. When the car sat for a week the oil drained out the filter. No big deal by itself, but the few seconds after starting of running with less oil pressure could cause a marginally dirty/tight tappet to hang up?