My E38 has 128,000 miles and I have had 4 occasions where the 'Check Coolant Level' would come on after the car is warmed up (indicator in middle position). The first 2 times were when I was driving without the lower engine cover on and the temperature was around 40 farenheit. I thought that because the cover wasn't on, it was triggering a fault. The last 2 times it happened were last week when the temperature was in excess of 100 farenheit (Colorado). This time the engine cover was on and the car was warmed up. I checked for visible leaks in the expansion tank but saw no leaks present. The trouble code goes away afer the car has cooled down and I've verified the correct amount of coolant is present. Just wondering if this is a simple coolant sensor replacement?
***EDIT: posting in the right forum would go a long way to getting you help and some answers.