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Old 10-04-2012, 03:51 PM   #29
Alex323Ci
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Join Date: Jan 2005
Location: Huntington Beach -Surf City USA
Posts: 16,866
My Ride: M3 & 323Ci (sold)
Quote:
Originally Posted by E46Mango View Post
Nope. i've personally seen and tested cooling systems using a pressure tester where cracked expansion tanks showed no leaks until heat was applied, then you'd see tiny droplets appear at the crack down the tank. Materials expand not only under pressure but when subjected to heat as well. If the crack was tiny enough to not show under pressure, it might expand just enough when heat is applied.
The way I suppose you "visually" saw a leak when hot and not cold is because it flowed up a higher waterline than the crack was at when cold (or not running). Visually seeing leaking is much different from watching the pressure cap gauge and reading the loss it gets after pressure is introduced in the closed cooling system.
There is no way a cooling system under pressure doesn't find a leak in the plastic(that's large enough to allow coolant out). This is physics. When the system is under pressure in the test with a PSI gauge in place of the radiator cap it'll show a drop if there is a leak anywhere in the system. The plastic is not going to close back up and seal it self to withstand this pressure. That is the very reason you're saying it expands to leak. Sure it can contract after heating but not to withstand a pressure test.

The Pressure Test Kit/Gauge you used was either faulty or user error if it didn't find a leak. Atleast you know now to have it checked.
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