What could be wrong when a 1999 Monte Carlo overheats and loses coolant?
My first guess is the intake manifold gasket. The best bet is to pressure test the system and see where the leak is/.
so where's the coolant going? down and out the tailpipe? in a pool under the waterpump, towards the transmission? not visibly anywhere, but simply dissapears with use?
One common cause of overheating and coolant loss is a bad coolant bottle cap. If it doesn't seal, it takes a lower temperature to boil the coolant. Tightening too hard or too often can damage the gasket and/or warp the bottle. --- check it out before spending a lot of time and money on tests.
If your not seeing a pool or it leaking, as already mentioned its possibly the gasket or a cracked head (as already mentioned) or even a bad cylinder wall. My car had the same dilemma, it was actually a cracked block, decided not to bother fixing it and just sold it off as is.
and RandyS is where now?...busy thumbin' it-
If it's the 3.8L V6 it's most likely the upper plenum and lower intake gaskets. If it's the 3.1L its most likely the head gasket. HTH. -Jim
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