[header] How to wash under the hood of a car [title] Make sure the engine is cold. [step] The only time you should wash under the hood is when the engine is cold. This means that you need to wait a substantial time after running the engine and washing under the hood. 
If you wash it when the engine is hot, you run the risk of damaging your engine as cold water may cause hot or warm parts to shatter or be damaged. [substeps] The best time to wash under the hood is in the morning after your engine has cooled all night.