Cleaned Spark Plugs, Ruined the Engine: What Went Wrong

The internet is full of “useful” tips on how to clean carbon buildup from spark plugs. Many drivers, however, don’t realize that today’s spark plugs are nothing like the ones used decades ago in older Soviet-era cars, where cleaning was sometimes actually part of routine maintenance. On modern vehicles, that kind of approach can easily end in a breakdown.

To put it simply: modern spark plugs should not be cleaned using old-school methods. Ignoring this rule and following questionable online advice can leave your car inoperable. Despite warnings and “horror stories” circulating online, some drivers still try using fuel, solvents, or other improvised cleaners.

One of the most common methods shared online is soaking spark plugs in rust remover or “rust converter” acid. Supporters of this method claim it removes dirt and carbon deposits effectively—and in a way, it does. After a short soak, the plugs may even look almost brand new.

But there’s a serious downside. Any rust converter, regardless of brand, is essentially an acid. While it strips away deposits, it also damages the extremely thin factory coating on the electrodes. Modern spark plugs often use precious metals like iridium and platinum for this protective layer. That coating is critical—it prevents overheating, melting, and premature wear. Once it’s gone, the plug wears out very quickly.

And the problem doesn’t stop there. Ignition coils can also be affected after this kind of “cleaning.” In many cases, they end up failing shortly after the spark plugs are damaged, leading to even more expensive repairs.

In the end, trying to save a few dollars on spark plugs can cost far more in repairs. The safest approach is simple: when spark plugs wear out, replace them instead of trying to clean them.