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Old 06-09-2003, 09:23 AM
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Join Date: Apr 2002
Location: RI
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Cooling System

83 300DT. I want to replace the fan and fan clutch on this car. Can I use the newer model withthe plastic fan from an 85? Will the existing shroud be OK? There's a sensor of some type right near the thermostat housing. Is this sensor used to turn on the AUX fan, the one in front of the A/C condenser? I saw someplace an ad for a sensor that turn's on a fan at 212 F. My car continues to run hot, nailed at 100C. It will drop when I turn on the heater but that sort of sucks in the summer. I've flushed out the radiator and cooling system and put in a new thermostat. The coolant and the flushing didn't show any heavy amounts of crud. Inside the thermostat housing was nice and clean. Prior to having this problem the car always ran at about 85 to 90 C even in the very hot days of last summer. No leaks, no coolant level dropping in tank. Any suggestions for fixing this thing? I need to use it for 200 miles per day next week and sure don't want it crapping out on me. Thanks Much
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Old 06-09-2003, 09:59 AM
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Join Date: Jan 2002
Posts: 18,355
From what I have read, yes you can use the newer fans in place of the olders, although I have never done the switch myself. It sounds as if your fan clutch may not be working. It should be fully engaged at a coolant temperature of around 95 degrees.
In a pinch, hotwire the aux fan to run all the time or put a switch by which you can turn it on and off.
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13
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Old 06-09-2003, 10:24 AM
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Join Date: Nov 2002
Location: Wakefield, RI
Posts: 2,145
I have posted this before but I will ask again. How do you know the gauge is accurate? Have you verified the true engine temp with a known outside thermometer or sensor? Many garages/mechanics have the laser point-n-shoot temp probes these days. I would verify that the guage is reading correctly before worrying about this. You might be chasing your tail changing parts and worrying when its just an old sensor or faulty gauge. That would suck, huh? I know, I have swapped 3 thermostats, all with different temp ratings and the guage never really moves from its normal spot. So I conclude the gauges are not really reliable. RT
When all else fails, vote from the rooftops!
84' Mercedes Benz 300D Anthracite/black, 171K
03' Volkswagen Jetta TDI blue/black, 93K
93' Chevrolet C2500HD ExCab 6.5TD, Two-tone blue, 252K
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Old 06-09-2003, 10:54 AM
Join Date: Jul 2001
Location: Old Lyme, Connecticut
Posts: 3,596

If the temperature drops and stays lower with the heat turned on it is not going to be a thermostat or a temperature sensor/gage that is the problem. In all likelihood it is the main fan thermostatic control that is not working, and it is possible the auxiliary fan could be faulty. Debris plugged or bent over fins on the air flow side of the radiator can contribute to the viscous style clutches not working, as well as degrade the heat exchange capacity of the system.

The radiator might be having some difficulty passing fluid due to corrosion products building up also but the same water passes through the cabin heater cores and if they are not plugged I would not see a reason why only the water passages on the radiator would be plugged. The heat exchange capacity of the interior heater is pretty small compared to the radiator and if turning that on makes a difference it is a signal that the system heat exchange capacity is down significantly for some reason. The major controls on capacity are the thermostat, then the main fan, followed by the auxiliary fan assuming the radiator water flow passages are ok.

If the main fan is not turning fast enough, or the air passages of the radiator are plugged with dead bugs and bent over heat exchange fins between water channels, you cannot get rid of the heat, especially at idle or low rpm operation. At higher speeds if the heat exchanger fins in radiator airstream are clogged or bent over, you still cannot get enough air through, and on the viscous clutched models the clutch will not engage because it works on the temperature of the air coming over it from the radiator. Not enough heat exhanged and the air will not be hot enough as it flows over the fan hub with the viscous clutch parts.

So, I would do a careful inspection of the air flow side of the airconditioning condensor and the radiator first. If either is plugged up there will be heat exchange capacity losses that could be easily corrected. Next is the main fan clutch. Check its operation, along with the auxiliary fan operation.

Good luck and I hope this helps. Jim
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

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)
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Old 06-09-2003, 11:44 AM
Posts: n/a
My car has been running hot for the past few weeks also. I have came to a conclusion that I still have some air in the system, and that the temp gauge sensor is bad. Sometimes the needle will bounce some. Here is what it will do, it will warm up and it will be above 176F, and it will stay there for like 15-20 minutes, then it will go up to the next notch and stay there and not get any hotter. Sometimes when I get the rpm's up high enough the temp will drop down some. A previous owner also added a switch to the Aux fan, and this sometimes helps cool down some, but still not that much...
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Old 06-09-2003, 02:20 PM
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Join Date: Sep 2001
Location: central Texas
Posts: 17,277
In the old days it was standard procedure to take the block , during a rebuild, to the "vat".... and they would really clean it out.
I suspect that that is not done in most cases with these old diesels... and anyway.... an old gas engine was likely to need a rebuild at half our engines mileage/age.....
So if you take the radiator out and are really trying to have it in the best shape you can I would suggest taking the core plugs or freeze plugs out... and using a 90 nozzel on a pressure washer to break what you can loose... and keep flushing until it is clean water coming out. I don't know if any access hole exists on the drivers side....
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Old 06-09-2003, 02:50 PM
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Join Date: Apr 2002
Location: RI
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Ok, at lunch time I went out and played mechanic. I found two wires leading off the top of the A/C Receiver dryer (not the pressure switch), shorted them together and the fan switches on fine. I'm going to short them out for this evenings drive home and observe the temp. I think the main fan's fluid coupling might be ok but I may replace the whole thing with a plastic fan a different clutch (different, not new :-) . I'm betting the aux fan's going to be enough for me to manage the next two week's anyway. I did use a 50/50 mix of MB coolant and distilled water. when I flushed out the block and rad there was really no evidence of corrosion. Last summer the car ran fine even on very hot days. It will only go a tad over 100C. Even stopped in traffic it goes no higher. I'm going to perform a test on the sender and since it's cheap, maybe just replace everything.
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Old 06-09-2003, 02:53 PM
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Join Date: Apr 2002
Location: RI
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And to 123c. Be careful what you wish for, my other car's a 2001 Subaru Forester. Blew it's headgasket, ruined the cats and O2 sensors all at around 40K miles. Fixed uner warranty but.....
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Old 06-09-2003, 08:16 PM
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Join Date: Apr 2002
Location: RI
Posts: 1,040
I hard wired the aux fan on and the temp stayed below 100C. It got pretty close in traffic but never hit 100. Went to 90C at road speeds. Don't know if it's an aux fan prob or fan clutch but I plan to replace the fan and clutch and put in a new sensor for the aux fan. Per another piece of info found here, I'm going to remove the aux fan and clean out any crap back there. I was able to stop the fan clutch by hand (Heavily gloved) with the motor idling at at full temp. Didn't feel like a real strong urge to turn but I don't know how strong it should feel anyway. The fan also wiggled a little so I'll just replace all that.
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