I have exhaust gas leaking into the water jacket.

On over head valve 4.0l engines look for a possible blown intake manifold gasket around passenger rear of engine. Head gasket jobs are labor intensive, and come with a high price. When an engine is pumping exhaust into the coolant it usually makes the coolant extreamly hot(your car would be overheating) and can even pressurize the cooling system and you would see rubber type hose blow out. To save sonme money go to your local auto parts store and buy whats called a block tester. Using block tester you will have a fluid blue in color and then you introduce a little bit of you vehicles coolant to test kit and you will see a color change if exhaust gasses are present, please report back and with some of the money saved make a donation to our site