Very slow Coolant leak.

[pberku]

My '95 E300 Diesel has had a very slow coolant leak for the last year or so. For the life of me I can't find the source. By a slow coolant leak I mean that I loose about 4 OZ. of coolant every 800 Miles or so.

The car runs fine, no overheating, consistently at 90F with the occasional 100F on very hot days with the AC in traffic. I did change the Expansion cap just incase.

I don't have any symptoms of a blown head-gasket nor a cracked block. No white smoke, no pressure in the upper Radiator hose when cold, no visible oil in the coolant, nor any visible coolant in the oil.

No obvious, or even traces of coolant leaks anywhere, not on the ground, not in the engine compartment, Not in any of the hoses behind the firewall, nor any leaks inside the car.

So far I checked the following:

- Monovalve,
- Auxilaiarry pump
- Water pump
- Radiator
- All hoses,
- Oil cooler lines,
- Winshield washer heater,
- Block Heater,
- Expansion Tank,
- Radiator, and Block Drains.

A pressure test of the cooling system revealed nothing. This is extremely frustrating. Where else can I look?

I would love to hear from anyone else that experienced and solved a coolant leak that was initially hard to diagnose.

Thanks,

Phil