1995 E320 Thermostat or Fan Clutch--Cold on Highway, Warm at Idle
 

Need help diagnosing a 1995 E320 that runs around 60*C on the highway and 100*C stuck in traffic. I resolved a similar problem on a 1990 BMW 325i by replacing the fan clutch...but I read that I shouldn't touch the W124 fan clutch unless I hit 105*C or greater. Previous Mercedes with thermostats stuck open never hit 100*C no matter the conditions. Car is new to me so I don't have much service history. P.S. I never hear the characteristic roar if I accelerate with coolant temp above 100*C.

Let me know what you think.

Thanks!

Luke

my 94 e320 has a seperate relay , for low speed fan fused in the rear of the fuse box, and a high speed relay fused in fuse box, the low is used when ac is on , i noticed one day my car was running hot , checked and found low speed fuse blown, these relays are green and blue, after i replaced fuse all is well, been a year since that happened, check yours

100 C is good to go. 60 is too cool. Replace thermostat. It is bad. Of this I am certain.

As for the fan, it's probably good. You'd probably be seeing an overheating issue in traffic if it wasn't. 100 C isn't anywhere close to overheating.

Forgot to mention my 94 normal temp is 80c , on a hot day extended stop maybe 90-100c

Luke, apparently the thermostat is stuck open, or partially open. I agree that you should replace it with an 87 degree C thermostat.

Thanks for the input everyone. I will change the stat and report back if any issues.

LG