If I change thermostat, will get back the heat.

What is the actual engine temperature after operating for 10 minutes?

Hello, definitely don't guess at anything here. As Pushrod suggested, checking the actual engine temperature as measured by the engine coolant temperature sensor (or by measuring the coolant temperature another way) is key to finding out why you have no heat. Is your inlet heater core hose too hot to touch, and the outlet one the same? They should be, when the engine is at proper operating temperature. www.repairpal.com/repair-shops