Water I leaking from my expansion tank .I Had pressure test and there was a small hole near the top. Had new expansion tank fitted ,but still leaking . I bought a new filler cap but it is still leaking what looks like from the top . There is coolant around the top ledge of the expansion tank. I make sure i screw it up tight enough , it seems like water is being forced out of the filler cap. The water goes down very slowly , I don`t have to put much water back in to fill it to max , but it goes below min after afew days.The engine does`nt over heat and the oil is ok . I changed the thermostat a while ago and changed coolant. Although when I bought it my mechanic friend checked the coolant and said there was a type of additive sealant in the water. It has been changed since then . can someone help this is doing my head in .
The water (coolant) in the expansion tank will rise and fall with the engine temperature. What the expansion tank does is collect and return coolant to and from the engine. When the engine warms up the coolant gets hot, builds up pressure and opens up the radiator cap. The coolant then goes into the expansion tank. Now when the engine cools down the pressure drops in the cooling system and the pressure drop (vacuum) pulls the coolant back into the engine via the radiator cap. The radiator cap allows the cooling system to build up pressure and by doing so increases the boiling point of the coolant, but when that pressure exceeds the caps rating the cap opens and the coolant goes to the expansion valve. The cap has another part to it that when the engine cools down and a partial vacuum is created in the cooling system a "valve" in the radiator cap opens and allows the coolant to be drawn back into the engine. I would look at your radiator cap to see if any gunk or build up is on it, and check the rubber gaskets for cracks. It's easiest just to replace the cap because they are inexpensive and easy to replace (2-10 dollars). The expansion tank should have two hoses on it. The one on the bottom comes from the radiator and the one on the top (possibly part of filler cap) runs down and is open to the ground. That way if it is overfilled or becomes overfilled it will slowly leak onto the ground. When and if you change your radiator cap, make sure the engine is cooled down, remove cap and start engine and turn heater to full blast, full heat. Leave the cap off and let it run until engine warmed up. This should burp out any air pockets that may have happened when coolant was changed. Also top off the coolant in the radiator while it is running. Hope this helps and good luck
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I did replace the cap but will try doing what you said , thankyou !
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