2003 Buick Park Avenue 3.8 Engine
The test to do is a coolant system pressure test. Pressurizing the system can help locate the leak most of the time.
Pressurize the cooling system and remove all the spark plugs, let it sit pressurized for a few minutes then crank the engine over. If a head gasket, intake manifold gasket, cracked head and or an engine block are leaking you will see the coolant spray out the spark plug hole that is closest to the leak.
Another way to locate a leak is to take the spark plugs out and pressurize one cylinder at a time with compressed air from an air hose and look inside the neck of the radiator to see if there are any bubbles. If you see bubbles then you probably have a bad head gasket or other issues related to the head or block near the cylinder you are pressurizing.
You can also put a dye in the coolant and drive the vehicle for a few days then check all around the engine compartment with a UV light (black light). If there is a slight leak then you will see a bright florescent lime green color where the leak is.
Remember to check under the dash board of the passenger side to make sure that the heater core is not leaking. If it leaks the rug will be soaked with antifreeze.
I hope these suggestions help.
I've repaired a lot of 3.8 liters with internal coolant leaks. First take a Digital volt meter, place the ground test lead to the negative battery terminal and place the positive in the coolant in the radiator or overflow bottle. If there is voltage. the coolant has became acidic. This eats away the aluminum around the lower intake manifold gaskets and the gaskets fail. To see if this has happened. Take the upper intake manifold off and you will see coolant sitting on top of the lower intake manifold runners. It may at first look like a lot of oil but the oil floats on top of the coolant. If so remove lower intake manifold. You will see the gasket will be broke or deformed. If you see any corrosion use a pick to remove it. I have seen them eaten all the way through, but not leak to the outside.
Last edited by tech1diesel (1/23/2012 2:34 AM)