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#1
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My 300E running too cool!
Hello gentlemen,
This one has me baffled. My M103 engine is running waaay too cool (or at least appears to be) at around 76/77 deg C fully warmed up. Sometimes it will run at this temperature with the ambient at 81F or 93F -- no difference, sometimes not, but if engine temp does rise, it'll barely touch 80c. Gas mileage is way down due to this condition. Occasionally I'll catch the needle "dancing" just a little. Things I've checked: 1. thermostat - changed it out, no difference. 2. coolant temperature sensor - my '91 M103 (103.983) has this sensor on the head itself (two pole blue). This was recently changed due to an aux fan problem, so I doubt this is the cause. I've double checked the connections -- no problem there. What should I check next? Does the coolant temperature sensor serve as the engine temp sensor? Are these two different sensors? The "dancing" needle leads me to believe that whatever sensor/relay/etc that controls it is bad. Please offer any insight you may have. TIA!! ~Paul _______________________ '91 300E, 212K miles |
#2
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Check your Engine temp sensor again. The connector post has the tendency to come loose and start rocking inside the sensor. This is probably the reason you catch the needle "dancing " sometimes. You also mentioned a sensor was replaced due to an aux fan problem. I believe that is a different sensor and while replacing it, engine temp sensor which is a single pole (black) and located in the same area got disturbed in some way and it went bad. Check it out.
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#3
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pmizell Amazing I have had the same problem and was going to post today .... except now it seems I am getting more normal readings. Must be a bad sensor.
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'03 E320 Wagon-Sold '95 E320 Wagon-Went to Ex '93 190E 2.6-Wrecked '91 300E-Went to Ex '65 911 Coupe (#302580) |
#4
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I've double checked the connections, no problem found. My newer M103 does not have an "engine temp sensor" -- MB calls it an ACC temperature sensor, and the parts page incorrectly states that it's located on the intake manifold when in fact it's on the rear of the head.
This sensor turns aux fans on high when 105c is reached, and cuts out ACC altogether when 115c is reached. Here's a pic: The older 103's had a 3 pole green terminal that ran thru chassis #-A-079037 and had the same function as my 2 pole blue sensor. It is called an "engine temp sensor", so I'm assuming this newer 2 pole blue is my "engine temp sensor". My chassis # is B-399221. Any other thoughts/solutions are appreciated! ~Paul _______________________ '91 300E, 212K miles |
#5
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I see someone else has discovered my signature avatar...DRAT...I need a NEW one!
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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 |
#6
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The instrument panel gage sensor cannot cause mileage to drop by failing to register the correct engine temp, can it? I did not think this sensor "spoke" to the engine controls.
My 1988 300E runs just below to just above the 80 degree Celsius mark, and never goes higher. While driving the car home from Utah to Connecticut I got 29.8 mpg or so and figured the temp was normal for the car. Did your car's normal operating temperature just change and get lower? My 1986 190E 2.3-16 has consumed two thermostats, with the symptom being it would warm up to its normal temp, about 82 degrees C, and then drop to about 70 or lower. Each lasted about 85,000 miles. And, at that temperature, mileage did suffer. Based on my experience your temps seem pretty close to normal, but the real test is "did it change recently and abruptly?" Good luck, Jim
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Own: 1986 Euro 190E 2.3-16 (291,000 miles), 1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000, 1988 300E 5-speed 252,000 miles, 1983 240D 4-speed, purchased w/136,000, now with 222,000 miles. 2009 ML320CDI Bluetec, 89,000 miles Owned: 1971 220D (250,000 miles plus, sold to father-in-law), 1975 240D (245,000 miles - died of body rot), 1991 350SD (176,560 miles, weakest Benz I have owned), 1999 C230 Sport (45,400 miles), 1982 240D (321,000 miles, put to sleep) |
#7
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Just a thought, but can a rich fuel mixture condition cause an engine to run cooler? I know it works the other way around. When we used to lean out our carbs and ran timing advanced for racing we almost always saw higher engine temps. Maybe your problem is too much gas!!
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#8
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I believe M103 uses this temp sender for the temp gauge here is pic
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#9
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brcrosson:
Thanks for the reply. Do you have a part number for that sensor? I do have this single pole sensor right next to the blue two pole on the head. Thanks! ~Paul ______________ '91 300E, 212mi |
#10
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The single wire sensor is the gauge sensor and can be checked
with an ohm meter. Here are the readings -C/Ohms. 60-110 80-67 100- 38 The gauge should read these temps at these resistance values |
#11
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Thank you Arthur!
Time to put my multimeter to use!
Thanks a bunch! ~Paul _________________ '91 300E, 212K miles |
#12
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Well the gauge sensor checked out OK, but I think I've identified the problem. The low temp readings I'm getting seem to be related to an intermittent high idle problem I'm having recently -- when idle is normal, so are temp readings, when not temp reaadings are low.
The high idle seems to be related to the throttle linkage/microswitch. When idle is high (1200-1300 in neutral) and I depress the microswitch roller, idle returns to normal. So I either need to adjust the linkage or replace the microswitch. Thanks for all the replies everyone! ~Paul _____________________ '91 300E, 212K miles |
#13
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I had a fluctuating gauge reading on my 300E and solved it by adding a loop of thin solder to the temp. sensor post to make a very solid physical connection to the press-on connector. It cured it! There was just too much mechanical slop in the connection.
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'76 240D-Sold '78 240D-Sold '85 300 SD, 165K-Sold '88 300 TE, 165K-Sold '64 Porsche 356C Cabriolet- under restoration '86 560SL 124K Miles-Sold '94 320E Wagon, 74K Miles-128K Miles JUNKED '06 E350 Wagon, 84K Miles 07 SL550, 14K Miles |
#14
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pmizell
part number for single pole temp sender is 005 542 10 17 purchase one from fastlane last week, hopes this helps |
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