Ako engine wash at least every 6 months. For undercoat its once a year. For good undercoats/rustproofing try the full rustproofing offered bt Tuff-Kote or Ziebart. For cheaper alternatives (only undercoat and not full rustproof) the ones offered by Shell or Caltex are also very good. The cheapest alternative is buying the chemicals per gallon (450 pesos/Shells Rustgard) and applying them yourself. Goodluck.