The two most common failures of the "metal crossover" intake manifold are breaking of the nipple for the heater core outlet (passenger side rear), and erosion of the retaining groove for the formed gasket seal in the crossover/thermostat housing to manifold plastic flange joint.
The inner wall of the retaining groove erodes and no longer contain the gasket, which pops out into the coolant passage, it not longer seals as it should and coolant leaking out is the result.
From the underside of the manifold it looks like this:
A new manifold is the simplest solution, however being retired and cheap I repaired mine with JB Weld:
If you choose this route proper surface preparation and degreasing is essential to success. I can fully explain how I did it if anyone is interested.
This was in February of 2011, at which time I also ordered a new FRPP manifold "just in case" the JB-Weld repair did not work. The new manifold is in my attic and of course now that it is there the repair will never fail...
- 2003 GT, UPR X, FRPP 24lb/h, Magnaflow, PP 70mm TB & plenum, Delta Force tuned,
Steeda UDPs, Ralco flywheel, RAM HDX clutch, 3.73s, 262 rwHP/305 lb-ft.
New ride (7/1/2013) 1998 Mercedes SL500-5.0L 32V VVT 326/347 HP/tq