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Mercedes Benz 300e Repair Questions and Answers

Question: 1989 Mercedes 300E 3 Liter Petrol mileage: 184,000. I would appreciate any help you may suggest for a problem I have with my faithful old Mercedes. It is a 1989 300TE, which I have had from 58,000 miles. Now with 184,000 miles and almost perfect bodywork, please tell me I don't have to change it! It started overheating and the garage local to my workplace (non Mercedes) identified that the fan was not working. A new fan however did not stop the overheating. A chemical test on the coolant identified that the head gasket was blowing. Subsequent strip down confirmed this as being on the 5th and 6th pots. After pressure testing, skimming and refitting the head, as well as changing out the thermostat, sender and a few other components, I still was left overheating. The radiator was then removed for testing, and re-coring carried out. The car now goes brilliantly, normally runs about 80 deg C, but still tends to overheat whenever I get in a traffic jam, and sometimes at other odd occasions. It hasn't actually boiled over, but the temperature gauge seems to fluctuate pretty wildly at times, sometimes going over 250 degree F before dipping back down again. I have checked that the fan is working even when the temperature gauge is showing hot. Whilst traveling in Germany recently (in a hire car) I saw several older Mercedes with their bonnets up on the side of the road during traffic jams. Is this a problem with older mercs? There does not seem to be any logical explanation. I have since had the coolant system flushed thoroughly with a proprietary flushing agent and checked the connections to the heater matrix etc. There is no evidence of blockage, although we have not removed the engine block core plugs. I have tried two different MB thermostats and two MB sender units. I am tempted to replace the temperature gauge, but the fluctuations only occur once the engine gets really hot. Any suggestions - I am getting desperate!

Answer: On other cars with similar symptoms, we have found that the veins on the water pump corrode to the point that it causes poor coolant circulation at low speeds. Therefore, check the pump and replace if you find that it is faulty.

Answer:    Assuming you have a factory-installed alarm, the control module is behind the right side of the passenger footrest near the kick panel.  It may or may not be adjustable.  More than likely, you have an after market alarm system, which is probably adjustable depending upon the manufacturer.  You should be able to disconnect the siren without affecting the rest of the alarm system.

Question:  1986 Mercedes 300 E  mileage: 124,000.   My car ran fine until the Antilock light went on then the car started losing volts. Any idea where to start looking?

Answer: Check alternator output and also check for a bad diode in the alternator.

Question: 1987 Mercedes Benz 300E in line 6 mileage: 221,000. My question is my 300E runs extremely hot when idling for a couple of minutes. It could be 30 below zero and if I stop moving for a couple of minutes, my temperature goes to red line. Yet, it has never boiled over. This is what I've done so far to try to fix the problem: Replaced the radiator, thermostat, and fan clutch, checked the gauges, and got the heads done along with a valve job. I pretty much replaced the whole cooling system, yet it still over heats. The only way I can get the temperature down at that point is either start driving, which I can't always do, or rev the engine a little and within seconds, the temperature drops. The car drives great and I have no problems with the car rather than the heat. I do not want to burn out the engine plan on having the car for at least another 100,000. Any ideas?

Answer: They only thing you have not replaced in your cooling system is the water pump. Your problem may be that the vanes in the water pump may have corroded off and is not circulating the coolant at low speeds.

Question:  1986 Mercedes Benz 300E 3 liter V6 mileage: 170,000. The problem is that the car has a problem starting from time to time and on occasion, it will stop when driving. The car will usually start after it sits for a while. We think it may be the fuel pump or one of the relays.

Answer:  If a major tune-up has not been done recently, this could be the cause of your problem. Replace the spark plugs, plug wires, fuel and air filters, etc. Also, replace the oxygen sensor. In addition, service the fuel injection system. Clean the carbon deposits from the throttle bore and idle passages. A faulty fuel pump may also be the problem.

Question:  1992 300e Mercedes 2.6 mileage: 120,000.  Bob/ken, speedometer just stopped working, both the odometer part and the mileage registration.  What should I look for as a laymen; some easy checks for me to do.  I’m not afraid to check things on my own.  Waiting for next move?

Answer:  Check the signal generator in the transmission.

Question:  1990 Mercedes 300E mileage: 123,000.  Hi guys, this web page is awesome!  I have a couple of questions regarding maintenance.  I believe my engine uses a timing chain and not a belt.  In any case, at what mileage would you recommend changing the chain (or belt)?  Also, it seems like some days, my car runs very strong but then once in awhile it feels very sluggish.   I know the honeycomb in my catalytic converter is damaged/loose.  Could this be related to the power loss or is it something else?  If the car needed a tune-up, I would think it would run poorly all of the time.  This problem seems to be more sporadic.  Thank You

Answer:  As a general rule, timing belts should be change at approximately 60,000 miles.  Timing chains have a longer life and are normally changed during an engine overhaul.  Your car has a timing chain.  As to your sluggish problem, if the catalytic converter is damaged, the exhaust is likely being restricted.

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