I've searched around and not really found a good answer to this. Let's say you had a Lexus GS300 and wanted to install a coolant filter. I understand the heater hoses are not always active, they are only active when the heat on. At least, that's how it is in my SC300. There is a coolant flow control switch inline with the heater hose coming off the back of the engine. I assume the GS has the same thing, but I admit I have not gone searching. Installing it in the line coming from the radiator to the overflow bottle would seem equally pointless. Am I missing something here?