Recently the car began losing coolant and the low coolant light comes on at the dash board. The rate of coolant loss is about 1 inch in the reservior per week but it is steady. The car has 150,000 miles on it and I am getting ready to replace all the hoses and the recirc pump as part of that service. Observation so far:

The car does not overheat and runs at normal operating temp when driven

The system remains air tight overnigt and you can hear it equalize when the radiator cap is removed

There are no signs of steam escaping when the car is idling and at operating temperature

There is no sign of wetness on any of the hoses, water pump, or radiator and no puddle under the car

There does not appear to be water in the oil

Except when warming up from cold there is no water vapor coming from the tail pipe

Where is the water going?

I recently replaced the plugs and they had tan to reddish residue on them that I have not seen before so I was wondering if that was a sign of water getting into the combustion chamber. The car uses a quart of oil about every 800 miles (I have a set of valve stem seals on the work bench).

Thanks for the help.

Just a guess but I'd say water pump. It's really hard to follow a leak from the weep hole and for some odd reason it can leak considerably without coolant hitting the ground. Maybe it only leaks at high rpm.

Sixto
95 S420
87 300SDL
83 300SD ... $950, see cars forum
91 300SE ... sold

Thanks Sixto.

When I have the cooling system apart I'll check it out. I probably ought to replace the pump anyway since I believe it is the original.