I tested Liqui Moly Sludge Remover to see how well it removed sludge from an old engine. A phone call to Liqui Moly headquarters in Germany helped clarify which product is stronger. Here's a hint, the said that their sludge remover product (# 5200) is not intended for the US market, but that the Engine Flush (# 2037) is. That doesn't stop 3rd parties from selling it on Amazon though.

Liqui Moly Pro-Line Engine Flush: https://amzn.to/3o93BMP
Liqui Moly Sludge Remover: https://amzn.to/40w6CIE

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