overflow coolant tank?
12-28-04, 10:27 PM
#1
overflow coolant tank?
can anyone explain what does overflow coolant tank do? i understand it holds coolant from filler neck. but does any coolant sucked back into filler nack? if yes, how?? oh, I have m2 ast eliminated kit. no AST. does this kit makes any circulation on cooling system?
12-28-04, 10:59 PM
#2
don't race, don't need to
Been explained a few times, but...
As coolant warms up via heat transfer from the block, the liquid expands. If the coolant system were "closed" and sealed, it could potentially fail (100 psi or more could easily be built up) explosively. Not good. So as the coolant expands, it is forced out a pressure relief, namely the spring on the coolant cap. In your case with the AST removed, this is the cap on the filler neck, though stock, the pressure relief occurs at the AST. Our cars are running 13lbs stock, which means once 13 psi of pressure has built up in the system, a bit of coolant is dribbled out to the overflow tank.
Once the coolant begins to cool (after the car is shut off, after the turbos have dumped their heat in to the coolant system), it naturally begins to contract. This creates a vacuum in the coolant system, strong enough that it could easily collapse hoses if there were no way for the coolant system vacuum to be released. Luckily, the "pressure" cap is really a two way valve. Look at the bottom center of the cap. See a little brass piece? Pull on that piece. It comes away quite easily (or should). This allows the system to draw coolatr BACK into the system FROM the overflow tank on shutdown. Thus, there should be no air in the system as it gets purged, and there is only coolant left.
Note that ANY small leak in the system that can't hold 13 lbs positive pressure, and around 2-3 inches mercury vacuum will cause this process to fail. The most typical case is a pinhole leak, where a small leak occurs when the system has cooled off and shrunk. When warm, it holds pressure, and all is well. When it cools, the hole opens, and air is drawn into the system instead of coolant. The level in the overflow starts to rise as you add more coolant to fix the low condition. Blown O-rings (or blown head gaskets in piston engines) act similarly, though there is typically more coolant lost per heat cycle as exhaust gases are forcing coolant out.
That what you were looking for?
As coolant warms up via heat transfer from the block, the liquid expands. If the coolant system were "closed" and sealed, it could potentially fail (100 psi or more could easily be built up) explosively. Not good. So as the coolant expands, it is forced out a pressure relief, namely the spring on the coolant cap. In your case with the AST removed, this is the cap on the filler neck, though stock, the pressure relief occurs at the AST. Our cars are running 13lbs stock, which means once 13 psi of pressure has built up in the system, a bit of coolant is dribbled out to the overflow tank.
Once the coolant begins to cool (after the car is shut off, after the turbos have dumped their heat in to the coolant system), it naturally begins to contract. This creates a vacuum in the coolant system, strong enough that it could easily collapse hoses if there were no way for the coolant system vacuum to be released. Luckily, the "pressure" cap is really a two way valve. Look at the bottom center of the cap. See a little brass piece? Pull on that piece. It comes away quite easily (or should). This allows the system to draw coolatr BACK into the system FROM the overflow tank on shutdown. Thus, there should be no air in the system as it gets purged, and there is only coolant left.
Note that ANY small leak in the system that can't hold 13 lbs positive pressure, and around 2-3 inches mercury vacuum will cause this process to fail. The most typical case is a pinhole leak, where a small leak occurs when the system has cooled off and shrunk. When warm, it holds pressure, and all is well. When it cools, the hole opens, and air is drawn into the system instead of coolant. The level in the overflow starts to rise as you add more coolant to fix the low condition. Blown O-rings (or blown head gaskets in piston engines) act similarly, though there is typically more coolant lost per heat cycle as exhaust gases are forcing coolant out.
That what you were looking for?
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