Three times now my dash Coolant Warning Lamp has come on while I'm driving. The first two times it was after about 20min of mostly Highway driving on my way to work. The light came on but the Temperature gauge was normal and rock steady at about 85 deg.. The light went out again after a few minutes. The 1st time this happened, I pulled over and checked under the hood, but everything appeared normal. No visible leaks, Top Rad hose was normally hot and pliable (no abnormal pressure), The coolant tank level was normal. I also checked again after it had sat for a few hours and all levels were normal.

Second time I was only minutes from the office so I kept a close eye on the gauges (normal) and kept going. Again light went out after a few minutes. The third time the light just came on very briefly when I was forced into some hard braking by the 'doughnut' in front of me , but went out straight away. Again all temperatures and levels appeared normal.

Any ideas anybody?

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1991 M-B 560SEL Arctic White/Grey 99,000 Miles
1987 M-B 300SDL Ivory/Palomino 229,000 Miles (sold but never forgotten)
2006 Volvo XC70 Blue/Beige
1999 Porsche Boxster Arena Red/Savanna Beige
1986 Porsche 928S Goldweiss/Brown