One of my spring duties was a coolant, hoses and thermostat change. While I had ordered and received the thermostat as part of another order, I hadn't bothered to get the o-ring or the gaskets for the various drain plugs. I'll just get those from the local dealer... NOT! No can find the part numbers much less the parts. So I'll just pull the lower hose and let it drain, since I wanted to change the hoses anyway.
Notice that the engine ends of the big hoses are both at the same height on the block. I guess that's why the engine has galley drains on the sides of the block. Hmmm- needed to pull the thermosat too for replacement, so out came that too, after loosening the fuel line that blocks access to the lower bolt there. Once that was out, I could see what a fine job the factory guys have done on the design of the cooling system. Most cars have a thermostat that stays closed until the engine warms up, blocking the flow of coolant through the radiator while the coolant is still cool. Porsche came up with the thermostat in the bypass position, so that the thermostat stays --open-- until it gets warm inside. That allows the pump to circulate water through the engine at full flow, eliminating hot spots and uneven warmup until it needs the radiator.
But how does this relate to changing the coolant?? Glad you asked! You can flush the block with the thermostat out by blocking the bypass port with a rag. Loosen both ends of the upper (passenger side on US cars) hose, and pull the radiator end free. Rotate it up so you can stick the hose in the loose end. Reach inside and push your shop rag into the bypass port, then turn the water on so that the hose fills the engine via the top hose. With the rag in the port and the thermostat removed, the water will flush through the block completely, including the lower galleys, and exit at the thermostat opening where the lower hose used to be attached. You'll change everything except the coolant that lives in the heater core, but that will drain when you change the heater hoses and the heater control valve. So, if this lucky set of circumstances happens to fall on you, there is a way to get all the old stuff out of the bottom of the engine without pulling any drain plugs.
Go ahead and run the hose into the top of the radiator too, with the radiator hoses removed. Just let the water run until it's clear from there too.
On the cooler thermostat-- The car runs a lot closer (on the gauge) to where I think it should, but-- It still goes up to the fan controller points when driving slow. Seems that although the new 'stat opens earlier, it still takes some airflow through the radiator to dump the heat. In warm weather and slow driving, the fans will cycle at temps higher than what you might expect, leaving the car to run at pretty much the same temp it did before on the hot days.
Hope this helps...
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