1998 C250TD not reaching operating temperature

[AusDieselTurb]

Hello all, my 1998 W202 C250TD benz at the moment (winter in the southern hemisphere) only reaches a "running temp" of around 62-65°C on the highway and when driven hard gets closer to about 70°C, but never reaching 80°C. The same is true even when it was warmer earlier this year only reaching about 65-70°C. Would it be a stuck open thermostat or something else, like just a faulty sensor perhaps? Thanks.

 

[Bogus]

Id bet on thermostat.

 

[ajlsl600]

Me too and cheapest starting place.followed by dud temp sender, try statt then put temp gun on statt housing afte a 10mile thrash.does that give same reading as in car?

 

[mioba]

take stat off and put it i a cup of boiling water.
Anyway it sounds totally like the stat.
A good time to flush coolant totally if it’s due with the stat out.

 

[AusDieselTurb]

Apologies for leaving this thread unanswered. Turns out the oring was due for a replacement, broke in half off the thermostat. Tested said thermostat with a thermometer on a stove and slowly bought it up to a boil. Started opening at around 80 degrees as it should, did a thorough coolant flush in the car, and it still sits in the same temp range. I've simply concluded that it runs cool if not driven hard, since when I do it sits at 80 no problem.