There's three tests that can be performed to find the source of the leak. The first is a simple pressure test. Many auto parts stores borrow or rent tools and they will have a pressure tester with a hand pump and pressure gauge. Pump the system up to 15 psi, then you can search for an external leak.
Leaking head gaskets are very common. When coolant can leak into the combustion chamber and go out through the exhaust, combustion gases can also leak into the cooling system. Most mechanics have a glass cylinder with two chambers partially filled with a special blue liquid. Air is drawn from the radiator through the liquid. If it turns bright yellow, the head gaskets are leaking, or more rarely, a head is cracked. Typically you will also see white smoke coming from the tail pipe and the exhaust will have a sweet smell.
For slower leaks, especially when the leaking coolant evaporates and can't be easily seen, you can add a small bottle of dye to the cooling system. After driving for a few hours to a few days, you search with a black light around the engine and inside the tail pipe. The dye will make a bright yellow stain that you can follow to the source of the leak. A gallon per week would probably fall into this category since the coolant isn't running out in a matter of minutes.
If your car still has the red Dex-Cool, (Dex-Mud) antifreeze, corrosion is a common problem. In particular, the heater core in the dashboard should be checked. There will be about a 4" long rubber hose hanging down from the passenger side of the firewall under the hood. That is the drain for the water that normally condenses when the air conditioner is running. If the heater core is leaking, coolant will also drip into that drain pan and run out the tube. The end that is hanging down will be molded into a slit, not a normal round hose, so you'll have to crawl underneath and shine the black light up into it if you're using the dye method.
Thursday, May 5th, 2011 AT 8:09 AM