anyone know the average engine temp reading on the dash gauge for a 1992 500SL...mine runs above the white dash after the 80 dash.... I think it is the 100 mark. Soit runs around 110..it has a C for celcius....so is 110 or so Celcius..waht is that in Farenheit and is it okay for a hot town like Las Vegas ?

Your thermostat should be set at *about* 85 C. Fans should kick on at 100 C. When idling in traffic or in hot weather, 110 is still OK for your engine. Anything higher and I might worry a little.
But if you do a search on engine/coolant temps... you will find a wide range of info on this matter...

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2006 E350 w/ 155k miles (Daily Driver)

Previous:
1993 300E 3.2L Sedan w/ close to about 300k miles
2003 E500 Brilliant Silver (Had 217k miles when totalled!)
1989 300E with 289,000 miles (had for <1 yr while in HI)
03 CLK 500 cabrio (Mom's)
2006 C230k (Dad's)
1999 S420 (Mom's/Dad's)
2000 C230k Sport sedans
2001 CLK320 Cabrio (Mom's)
1995 C280 My First Mercedes-Benz... (155k miles. EXCEPTIONAL AUTOMOBILE. Was Very hard to let go of!)

My 95 can run up to the 100 mark on a warm evening in Texas. Consider that the engine compartment is pretty tight in there, so heat dissipation is not optimal. IN that regard, I would suspect that the 300SL probably runs a bit cooler...

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2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car

That should be the M119 engine which is also in the 500E but with a different fuel injection system.

These are known to run "hot", especially in the W124 chassis 500E/E500.

Run a search (upper right) under "500E hot" and you should find plenty of info.