If the antifreeze isn't going on the ground then unfortunately it
sounds like a bad head gasket to me.

Blown head gasket, probably. Do a pressure check on each cylinder.  Also,
drain the oil and look at it - see anything that doesn't belong?  The
coolant is probably going into the oil.  Head gasket replacement costs big
bucks.

On 2/7/07 1:34 PM, in article
aRpyh.31707$Xq6.31421@bgtnsc04-news.ops.worldnet.att.net, "Tom Del Rosso"
<td_01@att.net.invalid> wrote:

A small leak can be almost invisible, as it evaporates on the hot engine
before you see it.  Look/feel around the ends of the radiator hoses, heater
hoses, thermostat housing, radiator seams, etc., first thing in the morning
before you start it up.  Any discoloration or wetness will be in the
vicinity of the leak.  Also, if the heater core is just starting to leak,
the only clue can be a slight anti-freeze aroma in the car and/or a gradual
build up of slime on the inside of the windshield.

Does it drop two inches and then stay at that level until you fill it back
up?  If so, check that the radiator cap is holding pressure and that the
seal is good in the hose running from the radiator to the overflow tank.  A
bad cap can let too much into the overflow tank and some of it will overflow
the overflow (and out onto the ground) while driving.  Its already gone when
you stop, so you don't see it.  When it cools and draws back into the
radiator, the level in the overflow tank will drop by the amount it blew out
the top.

1.  As others mentioned it may not be leaking while cold.
Consequently the fluid could mostly evaporate when the engine is
warm.  Look closely around all hose connections, etc., for any
evidence of residue.

2.  The expansion tank itself may be leaking.  Over time some of the
plastic tanks develop micro cracks that open up slightly under
pressure and leak but look fine when cold.  It took two months to
figure this out on one car.

3.  The heater core may be leaking.  You should be able to smell the
coolant in the car and the interior windows usually fog up a bit and
the fog doesn't go away with defrost on.

The smell of anti-freeze evaporating on a hot engine is unmistakeable.
Open your hood while the engine is hot and take a big whiff.  You'll
smell it if it's evaporating.

I had the same problem in my car, and every so often while driving I
would faintly smell burning antifreeze.  The smell got worse with the
heater turned on.  It turned out to be a tiny crack in the heater core
return hose.

 Check the water pump. Look at the bottom of the water pump for stains from
leaking coolant.