Diagnosing temperature issues on my S4
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Joined: Dec 2002
Posts: 5,283
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From: Australia
If your cap is opening early, it will commonly be releasing coolant when it shoudnt, so replacing the cap might be all you need to do. As the coolant expands with temperature, it will rise in the header tank, and if the cap's pressure is too low, it escapes.
jp 83 Euro S AT 54k
jp 83 Euro S AT 54k
Chronic Tool Dropper
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Joined: Oct 2001
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From: Bend, Oregon
Caps should probably be replaced every time you swap coolant. So every year or two. The factory Behr caps are inexpensive enough that you should have a new one on the shelf. Get them from your favorite 928 parts purveyor. Avoid the fitz-all caps at the parts places unless you are desperate.
With the correctly-functioning cap and the right dose of the right coolant, hoses that don't leak, etc, you can avoid a lot of overheating issues. A system that won't hold pressure allows localized boiling at 'hot spots', and that transition in and out of vapor state causes erosion of the metal parts as the coolant passes by. The uneven cooling strains gaskets too, like head gaskets.
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Several years ago, a used parts reseller in the northeast complained that people were trashing perfectly good used radiators by testing them at 15 PSI before installing them. Heck, why would anyone test a used radiator to see if the radiator would fail before the pressure-relief cap would relieve pressure? Hmmmm.
With the correctly-functioning cap and the right dose of the right coolant, hoses that don't leak, etc, you can avoid a lot of overheating issues. A system that won't hold pressure allows localized boiling at 'hot spots', and that transition in and out of vapor state causes erosion of the metal parts as the coolant passes by. The uneven cooling strains gaskets too, like head gaskets.
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Several years ago, a used parts reseller in the northeast complained that people were trashing perfectly good used radiators by testing them at 15 PSI before installing them. Heck, why would anyone test a used radiator to see if the radiator would fail before the pressure-relief cap would relieve pressure? Hmmmm.
