Coolant Light?




I am sure any coolant specifically formulated to protect aluminum engine parts will suffice for the small amount you will be adding but MB 325.0 (my jug says MB 325.1) Anticorrosion/Antifreeze is highly recommended. According to the container it is an Ethylene/Diethylene Glycol base with other additives. So Ethylene base coolant with aluminum protection would be your best bet.
Tap water is probably OK, but it has crap in it like fluoride and minerals. I doubt a M156 was designed to run on fluoride. Spend $1.97 or whatever for a gallon of distilled water - keep it in your garage and use it when you need to. Its cheap insurance on a $40,000 engine. And when you have your coolant changed, bring them 3 or 4 gallons of distilled water and tell them to use it.
Chances are, it's just a bad/stuck coolant level sensor. It will be tapped into the coolant overflow bottle. Unless the reservoir is empty, topping it off won't fix your problem. If the coolant expansion reservoir is empty, then you have bigger fish to fry than just topping off the coolant.
Use distilled water as noted in the post above me.
Alternately, go spend 40 bucks per gallon of Evans coolant and do a proper flush. You'll never have to worry about overheating so long as your coolant levels are fine. And the coolant will outlast your engine.
I want to make a remark though. The light use to lit more often when I parked my car on my garage car ramp.



