I’ve never really understood how it works on my Corolla. It’s a bit of an unusual set-up, at least compared to my truck. First off it uses something called a “bypass thermostat”. Second, there’s a weird metal tube that runs back behind, between the engine and the firewall. You can see it in the diagram below. On the diagram it looks like it goes through the engine, but it really is entirely on the outside . Labeled “water inlet pipe”.
Is that external water inlet pipe necessary b/c of the bypass thermostat design?
What exactly does a bypass thermostat do? Advantages and disadvantages to a non-bypass type?
Also, I’m getting some indications of a leak – blue-ish stains – at the point the water inlet pipe connects to the water pump. Anybody seen that too? Is it most likely the gasket? Or could it be the water pump is starting to spring a leak?
Click to enlarge the diagram, the 4afe is the top one.