There is no vent tube on the expansion tank. 4. Replace the coolant temperature sensor. I have a curious leak on a 1.9D expansion tank pressure cap. The BMW E46 coolant expansion tank is a part that commonly fails in all 1998-2006 3 series cars. Small leaks may produce steam and drips, while larger leaks will produce streams and puddles, as well as an obvious coolant odor. A coolant expansion tank is a common component found in most automotive applications. The coolant levels in your car's expansion tank should be inspected frequently because large drops in the coolant level could indicate a leak somewhere in the cooling system. The excess fluid flows into the overflow tube and goes into the overflow tank. Replace the coolant temperature sensor. - Coolant system is pressurised, this raises the boiling temperature of the coolant. A radiator cap can cause the system to boil and spit out all of the coolant. 3. The only brand of expansion tank and cap to buy is Modine and only Modine! The car seems on occasion to feel very hot and I noticed that I have a leak from the new expansion tank. After driving the car home, the coolant in the radiator had already dropped to the point where I couldn’t see it, and the expansion tank was 3/4 full. It is quite normal for coolant to be pushed out of the radiator cap. Remember to make sure your work area is clean and protected. What the expansion tank does is collect and return coolant to and from the engine. If coolant is coming out of the Reservoir fill cap then the Overflow piping is plugged. After driving the car home, the coolant in the radiator had already dropped to the point where I couldn’t see it, and the expansion tank was 3/4 full. So, I guess the $350 I just spent was in vain. 3. There is no vent tube on the expansion tank. It is quite normal for coolant to be pushed out of the radiator cap. This also could be a source for leak. I've noticed my 2006 CRDI seems to be 'weeping' coolant from the little drain pipe that sits underneath the cap on the coolant expansion tank. Give a gentle sideways push on the hose when the engine is hot and running, and it might spray more pink coolant. They are typically connected by a tube to the radiator filler neck, and can serve as a place for excess coolant to be captured when the pressure release valve in the radiator cap gives way. 4.Check and change fuses and relays for coolant … There is a hose leading from the pressure tank to expansion tank so any coolant leaking past the cap seal will flow through the hose in to expansion section Some photos would be better at telling the story. As the BMW E46 expansion tank ages, the prolonged heat and pressure it is subjected to causes the plastic to weaken. I've recently had coolant leaks and tried to find out where from as its been spraying around the top of the engine. I had a new thermostat and radiator cap installed. I am losing coolant through the expansion tank overflow pipe. These were all new items. I noticed the in-car heater was fine at first and then wasn't getting warm. Help with Coolant Leak (Expansion Tank, Radiator Hose) Hi All - I have a 1999 323i and for the past few months I've been noticing that my coolant has been leaking. The expansion tank and radiator are both under pressure at different times in the cycle: when the pressure in the radiator gets beyond a certain limit, an overflow valve releases coolant into the expansion tank - this lowers the pressure in the radiator, and increases the pressure in the expansion tank (assuming it is properly sealed and the cap is on tight). The small tube that connects to the tank from under the cover along the top of the radiator is a constant bleed from the hot tank of the radiator. Coolant escaping from under the cap on the expansion tank, I need advice. So, the radiator coolant overflow tank functions to serve this exact purpose. This also could be a source for leak. Anyway make sure that pressure cap is on the pressure tank and non pressure cap is on radiator. Inspect the tank body. as soon as i turned the engine back on it began to slowly bubble and creep up to the top of the expansion tank. 4.Check and change fuses and relays for coolant … temp is always reading normal when warmed up. but this has me completely confused. If you have good coolant and the radiator cap is new, then the thermostat could be sticking causing your coolant to heat up too much which in turn causes the system to boil. The braised hose also gets brittle. For a better experience, please enable JavaScript in your browser before proceeding. The cap is hollow and vents out under the 4 lugs that help you grip the cap to tighten it. Coolant leak from expansion cap - HGF? coolant leak from expansion tank cap? If you're sure there is something wrong with the cap then maybe contact LFP about a replacement. 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