SL/R129: temp. runnin past 90--what's norm?
Thread Starter
Junior Member
Joined: Apr 2015
Posts: 31
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From: so. calif.
1993 mercedes benz SL500
temp. runnin past 90--what's norm?
Drove my 1993 500SL with 96,780 miles on the speedo to the front end alignment shop (10 miles). Noticed temp got between 80 and 100. Not good?? Right.
I purchased this car back in April. Have had it torn apart restoring it. Down to getting it done and have to get it smogged by the end of this month here is So. Calif. Not pleased with temp setting that close to 100. Flushed out the radiator, didn't find any problems, nice and clean. Put the thermostat back in. I've ordered a Behr fan clutch for this engine. Old one seemed to be strong. Don't want to take any chances. Too many good miles left on this beauty. Any suggestions? All are welcome. james
I purchased this car back in April. Have had it torn apart restoring it. Down to getting it done and have to get it smogged by the end of this month here is So. Calif. Not pleased with temp setting that close to 100. Flushed out the radiator, didn't find any problems, nice and clean. Put the thermostat back in. I've ordered a Behr fan clutch for this engine. Old one seemed to be strong. Don't want to take any chances. Too many good miles left on this beauty. Any suggestions? All are welcome. james
Member
Joined: Jul 2013
Posts: 126
Likes: 5
From: Saint Augustine, FL
1998 SL500
The thermostat on the M119 doesn't fully open until 94 °C (201 °F), and the cooling fan's viscous clutch does not engage until 92 to 100 °C (198 to 212 °F) air is flowing over it (meaning the coolant temperature at the sensor is likely 5 to 10 °C hotter than that).
So, 80 to 100° C is the normal range depending on vehicle and engine speed and ambient temperatures--in very hot ambient temps (we hit 104° F here the other day) the coolant may reach 105° C while stopped in traffic. Without AC on the electric fans will not kick in until the coolant reaches 107° C, and will stop once it cools to 100.
Most newer cars have coolant temperature gauges with non-linear and dampened characteristics that keep the pointer more or less in the center of the range as long as the coolant temperature is within the "normal" range (80 to 120° C on most cars).
Our cars do not do this but instead show the actual temperature as it moves through the normal range--I.e. is is accurate.
I purchased this car back in April. Have had it torn apart restoring it. Down to getting it done and have to get it smogged by the end of this month here is So. Calif. Not pleased with temp setting that close to 100. Flushed out the radiator, didn't find any problems, nice and clean. Put the thermostat back in. I've ordered a Behr fan clutch for this engine. Old one seemed to be strong. Don't want to take any chances. Too many good miles left on this beauty. Any suggestions? All are welcome. james
Last edited by cliffyk; Jul 26, 2015 at 05:26 PM.
Thread Starter
Junior Member
Joined: Apr 2015
Posts: 31
Likes: 1
From: so. calif.
1993 mercedes benz SL500
Normal tempature
Thanks Clif...That's good to know. Yesterday here in Rancho Calif., it was over 100. Had the top down. I don't have the a/c charged yet. Once the temp guage read 100 the fans kicked on and the temp cooled a little. Sounds like it is working properly. Thanks for your help..james
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Joined: Jul 2015
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1991 500SL
I have 91 500SL with 74,545 miles, temp guage used to stay at 80C, then radiator blew, replaced radiator, all hoes, thermostat, fan clutch, tensioner, water pump and hood insulation, temp now reads about 85 C for normal driving on highway but climbs up to close to 100 in stop and go...guessing it may be temp sensor in need of replacement. auxiliary fans work properly, do not see any leaks of any kind.
Last edited by rbarr; Jul 29, 2015 at 01:36 PM.
Member
Joined: Jul 2013
Posts: 126
Likes: 5
From: Saint Augustine, FL
1998 SL500
I have 91 500SL with 74,545 miles, temp guage used to stay at 80C, then radiator blew, replaced radiator, all hoes, thermostat, fan clutch, tensioner, water pump and hood insulation, temp now reads about 85 C for normal driving on highway but climbs up to close to 100 in stop and go...guessing it may be temp sensor in need of replacement. auxiliary fans work properly, do not see any leaks of any kind.
Here are the electrical specs for the ECT and IAT sensors:
With a resistance substitution box like this inexpensive one from Elenco:
You can disconnect the sensor lead (it's just a NTC thermistor) and using the resistance box substitute resistances from the above table--the gauge readout should be approximately as shown in the table, ± 2-3% or so (which is very accurate for a dash gauge, but don't be surprised to see ±5%).
Last edited by cliffyk; Aug 1, 2015 at 01:19 AM.
