Hi my 87 300d temperature was running at or below 80 & the heat barely worked. It also has the 14 head. It's got 250k, 2nd owner, & always been taking care of. So I out an 80 degrees Wahler thermostat in it & now it's running 3/4 the way to the next line(assuming that's 100?).

Is this normal or too hot? Someone told me to put a 71 degrees one in but I would like the heat to work. It never teaches 100. I tried to see if it would go there but couldn't. The fan clutch works fine. Very worried due to the 14 head.

If you're at 80 or close to it, the heat should work pretty well. Have you investigated other causes as to why the heat is weak?

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14 E250 Bluetec "Sinclair", Palladium Silver on Black, 153k miles
06 E320 CDI "Rutherford", Black on Tan, 171k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver, 142k mi, wastegate conversion

19 Honda CR-V EX 61k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

With 80 deg C water temp, the 124 will make enough heat to roast you if it's working right.

I would go to the online factory manuals at startekinfo.com or w124-zone.com and follow the excellent troubleshooting guides there.

80 to 100 deg C is the normal operating range for these engines. The marking between 80 and 120 is 100.

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2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

The heat is definitely hot now but the car is running at about 90-95 degrees. It's was definitely not hot before I changed the thermostat when it was at about 80. I did flush the system too. Maybe that helped with the heat. It would barely run at 80 degrees this summer when it was 100 outside. The thermostat was definitely not working or maybe the flush cleaned up the sensor- if that's possible.

I was just worried about the running temperature running at 90-95 all the time because of the #14 head. Some of these threads get me so paranoid about it!

Thanks for your help!

While 90-95 is hotter than it should be, it's not hot enough to do any harm from everything I've read. Your aux fans would kick in at 105 or 107 (I forget which). There are a number of variables....might be somewhat difficult to figure out the cause.

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14 E250 Bluetec "Sinclair", Palladium Silver on Black, 153k miles
06 E320 CDI "Rutherford", Black on Tan, 171k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver, 142k mi, wastegate conversion

19 Honda CR-V EX 61k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

Get another tstat and test it first this time.

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1995 E420 Schwarz
1995 E300 Weiss
#1987 300D Sturmmachine
#1991 300D Nearly Perfect
#1994 E320 Cabriolet
#1995 E320 Touring
#1985 300D Sedan
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