I have a sodium silicate sealant in my car and need to find a way to soften it
I do not know much about engines, but from a chemical point of view, the clog that formed in your engine is most likely a hydrated silica. This compound is very insoluble and unreactive - there are only few things that can dissolve silica, e.g., hydrofluoric acid or a hot concentrated solution of sodium/potassium hydroxide, but I wouldn't pour any of these to an engine. Therefore, it seems that your only option is to dismantle the engine and try to remove the clog mechanically.