Got my '97 E39 back from the BMW specialist after it was overheating.

Turns out the thermostat housing was cracked, so he replaced the housing, the thermostat, and fit a new seal.
He also checked the water pump, which was thankfully of the metal impeller type, so it was OK.

The problem is that was the T/S the cause, or the effect?

So I've to drive it around for a few days and see if it overheats.

Today is day 3, and 85 miles later all looks well, but a hairline crack in the head could take longer to show up.
Anyone got any idea when I can relax and take my eye off the Temp gauge??

KP, did he replace it with a similar plastic housing or the upgraded aluminium type?  The plastic ones are known to give trouble and the al ones are recommended as the replacement.

KP wrote: Anyone got any idea when I can relax and take my eye off the Temp gauge??

3 days sounds good, but I had an issue with mine overheating a few months back which turned out to be a small leak and it would go away for a few days and then come back.  I still sweat every morning when I watch the temp gauge heading to that centre line and hoping it stays there.  It's a sinking feeling when you see it start to creep up to the red line, believe me...!!!

Got a new plastic one.
Still not overheating. Job was carried out by James Roe, so I'm happy that it was done properly.
Now, must check the coolant level when cold, and see if it's holding :)