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I had the same problem. Apparently I'm told it's a common complaint with 190 E's. It is because the coolant sensor (found in the front of the cylinder head) doesn't come in until the engine is touching 110 degrees. The oil pressure drops, revs drop, and panic sets in.

If you have a haynes manual look at: Carburettor fuel system, page 4A.10 and look at the diagram it should give you an idea of where the sensor is(you'll see the two prongs clearly visible).

I fitted a switch in the dash so I could switch it on manually at around 80-90 degrees to alleviate this.

To test the fan is working, all you have to do is bridge the two prongs on the sensor with a piece of wire (one piece of wire and put either end on each prong)and it should turn on to high speed (you'll hear a click). Then get some advice on how to fit a switch. It's not that difficult if youv'e got the patience and a few brains to pick. If you need any more help email me at

I don't have a wiring diagram, sorry, bat as to the overheating: it sounds like your thrmostate isn't opening--did you replace it along with the rad? Take the old one out and put it on a pot of water on your stove. It should open around the boiling point of the water--if not, you need to replace it. If it works, you may have a water pump issue i.e. your pump is not circulating the water/antifreeze. The only other problem would be the fan not working, but that would only be the problem if you are driving in quite hot conditions and sitting a lot in traffic.

Another way to find out if your thermostat is failing is to run the car for five to ten minutes and touch the lower radiator hose. If the lower radiator hose is cold then your thermostat is busted. This may sound stupid, but make sure there's coolant in the system and no major leaks before you try this test.


To prevent over heating remove the thermostat damage THE thermostat so the bottom port that the thermostat closes remains blocked this will force the pump to circulate through the whole system and shut off the bypass.

The electric fan is a little tricky (DISCONNECT THE BATTERY POSITIVE TO PREVENT EXPENSIVE DAMAGE). REMOVE THE AIR CLEANER. Trace the wire going to the Electra magnetic FAN coil below the water pump it has a in-line male female plug under the air cleaner unplug it tape up the wire going to the computer IMPORTANT. TO TEST hot wire the lead going to the fans Electra magnet you will hear and see the fan magnet click in.( DO NOT PUT POWER ON THE WIRE COMING FROM THE COMPUTER) now the circuit must run via a cut in sensor which is the red insulated brass sensor with 3 wires close to the thermostat housing on top and in front of the cylinder head. unplug the 2 connectors attached together this is your on off switch leave the single lone wire in its place. connect a wire using a 5 amp in-line fuse from the battery to the ONE SIDE OF the sensor using a slide on clip the other wire is from the Fans magnetic coil connect to the other side of the sensor they are now in the same place of the removed two prong plug tie the disconnected plug out of the way leave the old two prong plug disconnected. this completes the new Electra magnetic fan circuit the fan will cut in around 90+and out at 85 degrees on its own new powered circuit.

NOW MOST IMPORTANT your car will not start you have to fool the computer you have taken the fans Electra magnetic coil out of circuit AND IT MUST BE REPLACED you can do this using any 12 volt DC solenoid the wire you disconnected that used go to the fans Electra magnet must connected to the solenoids COIL and the solenoids most be well attached to the body work. your car will start and run with no over heating problems.

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โˆ™ 2011-09-13 13:30:06
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Q: Replaced the radiator in a 1992 190e 203 Mercedes Benz and car is still overheating what should you check also wiring diagram for thermostat housing?
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