It has to be going somewhere... When you fill it, carefully unscrew the bleed valve to make sure all the air is out the system. Then move the car to a dry spot (maybe drive for a while)...then park and see if you can see any leaks. Hoses all good? Be sure to look near the thermostat housing and water pump right under it. If anything is wet down there, its getting ready to go. That's how mine happened...I just changed both on mine last week. Hopefully you just running low on coolant.... good luck.
Very important!!! Do you have any smoke coming out of the tailpipes?
Had this same issue on my 2004 4.4 V8. If yours is the V8, I highly recommend replacing the entire cooling system. Basically the leak for me was in the water transfer pipe and the rear cover. The water transfer pipe can be accessed by removing the intake manifold, the electronics bridge, the fuel rail and the valley pan gasket. In order to get to the rear cover, You must remove the transmission, since it is right above the transmission itself in the rear of the engine.
So I figured, if I'm going to go through all that work, might as well replace the entire cooling system which involves: replace belts, pulleys and tensioner, pcv's, reservoir tank, all hoses associated with the cooling system, water pump, thermostat, radiator, all the gaskets and other electrical gizmos related to the cooling system, like fan auxiliary switch and another plug that goes into the thermostat, water pipe and the two o-rings associated with them.
But, if you're going to go through all that might as well replace the air filter, oil, oil filter, spark plugs, spark plug tubes, valve cover gaskets, front timing cover gaskets. By going through this, you'll be able to see the condition of your engine such as sludge build up, chain issues, valve condition etc.
I ended up doing all of this, some as preventative maintenance and some needed replacement.
I purchase all parts from ecstuning.com. They sell a cooling system refresh kit for our cars which includes almost everything. It costed me a little less than 2 grand for all parts, all fluids and I needed a few tools from harbor freight. In the end, my car runs brand new. It did however take me about 40 hours of labor and diagnostics to make sure everything is running as it should be.
If you have any questions, feel free to message me, I have plenty of videos and pictures saved from me doing the work, as well as bookmarked all the important pages and posts that helped me along the way.
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