2012 Coolant Overflow Bottle Has Two Caps?

wstar

The two systems (pre/post- 2012) work quite differently. You can see the differences pretty clearly in the Service Manuals (which are on the forums here in PDF, somewhere).

Basically, the earlier model has a non-pressurized overflow tank with a plastic screw-on cap, a metal pressure-relief cap on the water outlet (with just two thin hoses; waterneck -> tank -> ground). On these earlier models the outlet pipe on the driver's side of the engine (hard metal pipes with coolant hoses attached, can't miss em - Service Manual calls it the Heater Pipe) has only 3 connections on it: two fatter ones for the bypass flow to the rear water outlet and for the heater circuit, and a thin one poking out the top for the throttle body coolant lines.

In the new design, the non-pressurized overflow tank is replaced with a pressurized expansion tank (which is a much better design in many ways). The water-outlet cap is now a fixed cap (only remove for filling the system), and the pressure-relief cap is on the new expansion tank. The expansion tank has one more connection to it than the old overflow tank - the line from the bottom which goes to a new connector on an updated version of that metal Heater Pipe assembly on the driver's side of the engine (so if you want to convert factory-style, you need to update that Heater Pipe as well). The updated Heater Pipe, in turn, also has another new connection which goes to the new oil cooler down at the oil filter - so if you just wanted to update the expansion tank setup + pipe but not add the 2012 oil cooler, you'd want to block off that 4th connection. If you did want to add the cooler, then you'd also need to sort out the connector pipe for the other side of it, which is another separate piece. esfourteen's connection to the TB coolant connector is probably the easiest route to take, assuming you don't need the TB lines (don't live/drive in a cold climate).

The expansion tank is part of the real cooling system and runs full pressure, unlike the earlier overflow tank. The two connections (to the front/top water outlet area and to the side Heater Pipe) are what let air bleed over into the expansion tank where it should be, and let's the liquid sit in the tank at the correct level to use it as a gauge, but you won't see a lot of actual flow through them (since the connectors are perpendicular (or in the stock setup, backwards on the big one) from the normal flow).

Keep in mind if you run that connection to the TB coolant connector to route the line low - if you let it arc up in the air higher than the tank, bubbles won't make it to the tank as well (because the hose rather than the tank is the high point).

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