My friend'* 98' Malibu with the 3100 engine is leaking coolant. he said the mechanic told him it was a headgasket that was leaking. Checked the oil and there isn't any coolant in there but the coolant is going somewhere and FAST! he drove it just 20 minutes and the radiator overflow resevoir was emptied in that amount of time. I looked for external leaks but didn't see any (it also doesn't leak any fluid onto the ground.) This engine has 108,000 miles on it too so it'* surprising it'* having so many issues. another issue is a loud valve tap/grinding noise coming from the front, driver'* side of the engine. The engine is sounding really bad at this point of time. Anyone have any ideas? I don't know hardly anything at all about the 3100.

Lower intake manifold?

right on i have a friend who has a 99 MC with the same problem and also same engine

In the older engines ( pre-2003 ish) they were bad for piston slap. It can get pretty loud especially on cold startup. They are all ( 3100 and 3400 ) known for intake leaks, even up to 2003. I am just waiting for the day mine starts to leak. If that much radiator fluid disappeared have you checked to see what was coming out the exhaust?? You would see more smoke than usual. If I am not mistaken it will be white in color so it may be hard to see.

yer, and IIRC, it'* sweet smelling too. The catch is, this burning coolant could be the lower intake manifold... or a head gasket.

Mine went at 92k. Last Christmas. It was all in the crankcase. I changed the lower intake gaskets, head gaskets and had the heads cleaned and checked for cracks and warpage. That was last Christmas. I now have 120k and the engine has never been loud at all. I have some very MINOR piston slap at startup for about the first minute in the morning and thats it.

If its burning the coolant, then its probably the lower intake. These engines, as I have found out, are BAD about this.

I run Mobil1 in mine and its all highway miles, might be why it still runs so quiet.