Whats classed as overheating?

[golferson]

my temp gauge usually sits at 80-85 (ml270) sometimes uphill nearly 90, today
on M1 20 miles at 65-70 suddenly stuck in traffic nearly got to 95. also after driving at normal temp if I switch of,and restart after 30 seconds its climbed a few degrees although its not been running! normal or pending problems?

 

[panason1c]

'Normal' would be up to 100 degrees, (the engine fan would come on at, or around this mark) this would usually occur when towing or a long uphill climb and also during hotter days (ambient temp). Its normal for the engine temp to climb a few degrees after switching off as the heat builds slightly due to no air thru the rad.

Yours sounds perfectly normal to me.

'Overheating' would be when the temp passes 100 degrees, and always when the needle moves into the red area.

 

[golferson]

as ever your prompt replies are much appreciated, thanks for the reasurance

 

[wemorgan]

Under pressure water mixed with coolant boils nearer to ~120C. My fan kicks in @ 100C.

So I'd define overheating as >110C

 

[spike60]

Sounds fine to me too, my CLK 320 is very similar. Not a Merc, but my Corvette runs about 94c on the open road with the first fan coming on at 108c and the 2nd joining in at 113c. It's fine.

 

[SavMan]

The engine and bay will continue to heat after you have switched off, remember there is no air flowing either by driving or through the fans when the car is switched off and coolant has stopped moving so absorbs the heat. What you have described seems normal.

 

[bedwards1966]

As said, no need for worry - those figures seem fine.

It's actually very common for engines to boil after they've been stopped, but not when running. It's mainly because the coolant pump has stopped, so the coolant isn't getting pumped though the radiator and it just sits in the hot engine, hence the temperature increase.