Genuine Toyota 90916-03075 Thermostat We had a Toyota vehicle towed into the shop the other day and the customers complaint was that it was overheating. The repair shop replaced almost everything in the cooling system and still had this issue so the customer wanted us to step in. We knew from talking to the customer that the shop was using aftermarket parts, so after inspecting the outside on the cooling system and not being able to find any visible leaks (the cooling system was full) we decide to start inspecting the parts that were replaced. The first items we could easily get to were the thermostat and water pump. These two are very close together and we could inspect both at the same time. The problem we encountered was with the thermostat positioning. Here is a shot with the housing removed... As you can see, the "jiggle" valve is positioned straight down (6 O'clock position) which doesn't allow for trapped air to bypass the thermostat. This creates a air pocket in the cooling system, specifically in the block. While we were there we used a electronic bore-scope to we if the water-pump fins were intact, and not loose.... they were fine.... So we decide to installed a new Toyota OEM Thermostat, this time installed correctly. This is how Toyota thermostats are advised to be installed by the repair manual... So after installing the thermostat correctly.... the vehicle was fixed.... Always remember that the thermostat's "jiggle" valve is designed to let any air trapped in the system work its way back to the radiator/overflow tank and it's positioning is important.