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  #1  
Old 07-02-2007, 05:46 PM
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400E Radiator

Hey all,
My radiator has been the cause of some troubles recently. My car has been heating up to excessive temperatures, now that it is summer time. In the winter it hangs out around 80, but in the summer it hangs out just above 100. Lately it has been heating up to around 120, usually turning on the heater lowers the temperature down, except sometimes it takes a lot longer and doesn't bring it below 100, which it usualyl does when I turn on the heat. I feel like the overheating is boiling away some of the radiator fluid. Does anyone have experience with this? My radiator fluid light comes on after not driving for a while, and usually stays on for a minute or so, before turning off. I changed all my air filters, and oil and filter, but there wasn't much of a change. Adding fluid usually helps for a while, but after a few days its the same thing. Is this just overheating? Or could it be a leak? Or is it overheating caused by a leak? Are there any known weaknesses in the line where I could look for leakage? Thanks.
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Old 07-02-2007, 06:21 PM
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Are your auxilary fans coming on at all ? Are the temps this high even when you are driving on a freeway or just in stop-n-go traffic ?
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  #3  
Old 07-03-2007, 09:47 AM
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Try replacing the radiator/overflow cap. It sounds like it's leaking. You need to find the leak.
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  #4  
Old 07-03-2007, 10:35 AM
david s poole
 
Join Date: Mar 2005
Location: dallas
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yes you need to pressure check your cooling system and check your cap,then you can start considering your radiator.
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  #5  
Old 07-03-2007, 10:38 PM
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Join Date: Jun 1999
Location: Sarasota, Fl.
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I had to replace my overflow tank a few months ago. It has a sloooow leak around the neck (where the cap fastens to).
Once you pressurize it, you ought to hear it fairly quickly (unless there's a guy with a jackhammer next to you)
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  #6  
Old 07-05-2007, 01:13 PM
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I don't think the auxilary fans are coming on, but I definitely feel like there might be a leak in the radiator system somewhere. Where did you get your new overflow tank? I'll also get a new cap, hopefully that can be obtained at the same place that might have new overflow tanks. Any recomendations for parts to use and where to get them? Thanks.

Is there anything that can be done with the auxilary fans? I've had troubles with these before this even happened. Basically, they rarely come on, and never when I need them, so at red lights my car heats up and traffic. But also, after driving it for a while, it heats up a lot just sitting there because the fans don't come on.
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Old 07-05-2007, 02:07 PM
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The the temperature you have mentioned, the fan must come on. If not, then you have to check:

1. the fan's fuse
2. the fan's motor, you can check resistance across its terminal to see if the winding is not open. You should get a low resistance in a few ohms across the winding. If the winding is o.k., apply 12 V directly to the fan to see if it is turning. If the fan works directly, then need to check sensors that activate it.
3. There is a coolant temperature sensor somewhere on the engine, on my 87, 260E, it is the second last from the windshield side. This is actually a switch that closes when the engine temp is high. NOTE: on some models, this sensor may have 4 pins rather than 2 and you will have to find which two belongs to the aux fan. The other two belong to a signal that goes to the a/c relay. Take the connector out and short the two ends that correspond to the fan to see if the fan comes on. If it does, replace the sensor. If it does not, just connect both the pins to battery ground, if the fan still does not come on
check the aux fan relay. On my 87, 260E, it is K9 in the relay box.
4. Check pins 3 and 4 on the relay socket, they should have approx 12V. If they do and the fan still does not start, replace the relay. if you dont, then check fuse (fuse D) and wiring to the socket. If this is the problem, post again and I will look up further.

Another way besides a hot engine that triggers the aux fan is if there is high pressure in the refrigerant line.

One way to test the aux fan even when the engine is cold is by setting the a/c temp to minimum and running the blower motor at the highest speed. If the motor comes on, it tells you that the motor is fine. If it does not, you still have to do the above tests to find out if there is a problem with the fan/relay or that your a/c push button unit is not sending the right signal.
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  #8  
Old 07-05-2007, 07:28 PM
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The fans could also not be coming on at the low speed. My E420 is about to have its 4th repair for this. It is either the resistor, or more likely, the wire going to the top of the resistor - it gets too hot, and fries itself off.
In my car's case, it has been the resistor once, and the wire three times.

Once you turn on the A/C, the low speed should come one shortly thereafter. If it does not, and the car gets quite warm (the A/C won't feel so cool either) the high speed fan will eventually turn on, and cool things down.

The idiot that ordered the degradable wiring for the harnesses is probably the same idiot responsible for the resistor wire being too small.
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