coolant at the bottom of the intake manifold on 1999 Lincoln Navigator

99 lincold navigator. 5.4l sohc Coolant is coolecting in the bottom of the intake manifold. Causing excessive white smoke. I replaced the upper and lower intake gaskets. 10 miles later coolant was sucked down in the manifold again. Any ideas?

by in Sun City, CA on November 18, 2010
1 answer 2 comments
ANSWER by on November 18, 2010
The composite intake manifold on the 5.4L and 4.6L V8 from the late 90's had issues with developing hairline cracks, especially around the thermostat housing. Look closely for signs of cracking. Although your model was not particularly succeptable, it is a likely cause of your issue.
COMMENT by on November 18, 2010
Thank you for your response. I will look closly at this. I performed a block test and found no exhaust fumes in the coolint system. However the lower intake manifold is a plastic composite, it obviously holds coolant.
COMMENT by on November 18, 2010
Other Triton engines with a very similar (if not exact) intake were offered extended warranty coverage for this problem -- it was that much of an epidemic. Best of luck.