the switch that i am talking about is the by metal switch that switches on the magnetic cooling fan at 100 degrees it is the orange switch shown in my first post the switch has 3 connections one by itself and 2 together the 2 together can be shorted out and the electromagnetic fan will engage

if this switch fails your engine will overheat which could cause your Head gasket to fail as shown in images in first post. weakest point and pump oil into cooling system.

the only wax operated item is the thermostat which keeps the cooling water in the block until it opens approx 87 degrees to allow water to flow into the radiator and circulate throughout the cooling system

the attachment shows the switch that switches on the electromagnetic fan.

and as Rorypff says good quality water and a good quality additive

I use the same water you would put in a battery (Distilled Water) and i use Castrol corrosion inhibitor / cooling agent my choice.

I hope this helps Sydney from down under

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Replacing the head gasket is doable by an average mechanically inclined guy like you as long as you have the MB manuals and the tools to do the job. Of course it might take you the whole weekend to do it compared to a pro who can do it in half a day. But while you're at it, I suggest that what ever money you save on labor should be spent on sending the head to a machine shop for cleaning and recutting.

I recently replaced the head gasket on my '88 260e with m103 motor due to a slight external coolant leak.

After getting the old gasket off, I noticed that there were small holes in the gasket designed to evenly regulate the coolant flow through the head passages. Some of these holes were corroded and oversized, probably allowing too much coolant through and starving other passages. I can see the same thing in some of the posted photos in this thread.

What I'm getting at is that even if a head gasket is not leaking, it might still be in need of replacement, especially if it is close to 20 years old as in my case. I changed the coolant every three years using the Prestone orange stuff and distilled water, and figured if I not done that, The head gasket might have lasted half as long.