Coolant Leak Suggestions

[jbhebert]

Car is a 1995 E300D with 169,000 miles. I just recently started loosing about a quart of coolant every 5 to 7 days. I cannot find any visual clues to where it might be leaking. I do not get a coolant smell in the cabin or film on the windsheild that would indicate I have a heater core problem. I do not get any fluids under the car when parked. Oddly enough, my low coolant light usually comes on it is after the coolant has warmed up and I've been driving a while. I'd figure it would be more likely to be low when cold and not expanded. Anyways, I'm wondering if perhaps it's time to replace the expansion tank cap. I'd had vehicles where the cap failed and couldn't maintain pressure, and coolant would blow off while driving and the system would be low. It also appears that when the car is cold the coolant system is under vacuum. Is this normal for this car? Anyway, would this be a good first step? Maybe the tstat as well? Anything else to look for?

Thanks in advance.