What are common warning signs that my JDM engine needs attention?

Key warning signs: blue smoke on startup (worn valve seals), white smoke under load (coolant leak or head gasket), black smoke (rich fuel mixture), oil consumption exceeding 1 qt per 1,000 miles, coolant loss without visible leaks, knocking or tapping sounds, delayed startup, rough idle, or check engine lights. Address promptly to prevent major damage.