300E runs hot with A/C on....HELP!!! - PeachParts Mercedes-Benz Forum

mike690003 · #1 08-24-2003, 06:17 PM

Hello Board,

I rarely use my A/C, but today I decided to use it(it was really hot). My temp is usually about 85-90 C . Well I turned on my ac and right as I got into havy traffic the temperature started to climb. I went all the way to about 110 C. Well I had my expansion tank and cap replaced and I also had the cooling system flushed. My cooland/water mixture is a perfect 50/50. I have no leaks, What could have caused my car's temp to run so hot???

Do I need a new thermostat??? If so, what kind? a colder or hotter one???

Help!!!

psfred · #2 08-24-2003, 06:46 PM

110 C is a bit hot, but not catastrophic. Check the operation of your aux fan (does it run with the AC on or not? It should). It should also come one at 100C, and the visco clutch should lock up and cause considerably more noise when then engine is that hot.

Usual culprit here is a bad visco clutch, closesly followed by a bad connection on the resistor for low speed aux fan operation so you don't get a fan until 100C.

Peter

BobK · #3 08-24-2003, 07:55 PM

I'm not sure the temp, but somewhere along the line, your a/c Compressor should shut off and the AUX fan come on. This is controlled by a temp. switch on the head. It has two connectors on it. one two wire and one with only one wire. The plastic in the sensor is probably green. Thing went bad on my daughter's car. A/c would not work and fan ran whenever the key was on. Pain in neck to change. You have to pull the valve cover to get a wrench on it

mike690003 · #4 08-25-2003, 05:54 PM

I forgot to mention that I have a brand new aux fan. Could it be the thermostat???

psfred · #5 08-25-2003, 08:51 PM

Could be, but if it is, it will get that hot without the AC, too, generally.

Does your aux fan actually run (new or not, if ti ain't spinning, it ain't movin air....).

How old is the radiator?

Does the visco clutch work (do a search).

Peter

mike690003 · #6 08-29-2003, 11:45 PM

I replaced the thermostat today. It helped a lot. The highest the temp reached was 105 C . I am still looking into what could be the culprit of this problem. My car usually ran at 90 C on a hot day with the AC on high.

Duke2.6 · #7 08-30-2003, 01:19 AM

As these cars age, the radiator tubes develop internal deposits, which reduces their heat exchange efficiency. Significant deposit buildup would be normal if the cooling system has been serviced with conventional green antifreeze.

If the car has only been serviced with MB antifreeze or Dexcool, deposit buildup will be less because these formulations either contain no inorganic salts (Dexcool) or a very minimum amount (MB brand). Though inorganic salt formulations can be effective in controlling corrosion, they precipitate out and clog the tubes.

The engine driven fan clutch should nearly lock at about 100C and you should hear fan roar above about 2000 revs. The electric fans should activate at high speed at about 110C. If fan operation is normal, the most likely culprit of consistent hot running is probably a loss of radiator efficiency due to deposit buildup.

Duke

1991300SEL · #8 08-30-2003, 11:14 AM

Duke hit the nail on the head.

How often do you read here where someone replaced anything/everything related to a 15 yr. old cooling system only to still have an overheating problem.

Internals start clogging over time and head gaskets develop slight leaks which cause pressure loss, followed by increased temps.

McDiesel · #9 08-30-2003, 02:41 PM

have a 92 turbo diesel with same problem however alldata site sez the following in a T.S.B. mind you this is for a 92 turbo diesel

Cooling - High Coolant Temperatures

MD-NET ADMINISTRATIVE MESSAGE

DATE: JULY 22, 1994

MESSAGE #: 322

TO: ALL DEALER SERVICE MANAGERS / ALL DEALER PARTS MANAGERS

SUBJECT: GROUP 20 - ALL MODELS, COOLANT TEMPERATURES

The coolant temperature of MB vehicles may rise substantially above 100°C/212°F at high ambient temperatures while the vehicle is:

a) stopped
b) in city traffic ("stop and go")
c) when driving uphill
d) when driving at very high speed, i.e. with high engine load

Engine coolant temperature returns to "normal" upon returning to regular driving conditions. In individual cases, the temperature reading may approach the red field of the temperature gauge.

Provided the cooling system is well maintained and in good working order, such temperature levels do not create any danger for the engine and, therefore, give no cause for concern. The boiling point of the recommended coolant mixture (Refer to Service Information 20/9 and Service Microfiche group 20), is much higher than 1OO°C.

Copyright © 2003 ALLDATA LLC
Terms of Use

McDiesel · #10 08-30-2003, 02:45 PM

REMEMBER THAT INFO WAS FOR A 92 2.5 TURBO DIESEL

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