Does the 2008 Toyota Sienna have a timing belt or chain?

The 2008 Toyota Sienna does have a timing chain. The spark plugs need to be replaced every 100,000 miles unless it's a copper one. A cooper spark plug needs to be replaced every 30,000 miles. Your air filter needs to be replaced every 15,000 to 30,000 miles. The coolant needs to be replaced every 60,000 miles. You will come across many issues with an engine. A gasket may be loose and that needs to be tightened up. A spark plug may pop off, causing engine issues. A serious problem is the engine overheating. This may lead to fires and the vehicle exploding. There could be excessive oil use, requiring the oil to be changed sooner than expected. You can have oil leaks and those need to be repaired as soon as possible.