Ok so I am no car genius but I am not completely hopeless either. But I have a problem that is confusing me. In my 1990 300SL, my washer reservoir has filled with overheated coolant. I made the mistake of putting the wrong coolant into the car when my "add coolant" light came on. I also remember needing to add washer fluid. But I have a separate indicator light for washer fluid. Because of my rookie mistake with the coolant, I have had to replace the water pump, thermostat and the camshaft position sensor, which broke when trying to remove the pump.

So we got it all put back together, flushed the system and added the antifreeze. I was happy thinking I would be able to drive my car again. WRONG! In less than 2 miles I was nearly redlining and I pulled over. The coolant was boiling behind the dash worse than ever and smoke and steam were billowing out from under the hood at the passenger side. I finally got the car home and parked it. In the morning a HUGE stream of fluid had come from below the car. I drove the car around the building and into the hangar, maybe 2 minutes, not even time for the car to warm up and there was a coolant pool beneath the car. I inspected the location of the steam/smoke from the day before and discovered it was from the coolant overflow tank cap. Tightened it and thought the problem was solved. This was when I changed the thermostat because they didn't do it when the put in the new waterpump. Got it done, ran the car to inspect for leaks up to operatiing temperature and was getting a large leak still. Turned off the car, checked the cap again, nothing even though I could clearly hear the boiling in the reservoir.

And then I realized. It was coming from the washer reservoir not the overflow. The fluid was being forced out around the washer cap. Opened it up and thought "oh crap, did I put washer fluid in a coolant reservoir? No wonder everything failed" I squeezed the upper radiator hose to be sure and sure enough it bubbled into the washer tank. I checked my owner's manual to make sure I'm not crazy and it is in fact the washer tank.

So after my long winded explanation, my question is How in the world did my washer fluid and my coolant get mixed together like this? I was confused and concerned when I opened the radiator drain plug to remove some coolant and it appeared to be green. (I used the Zerez-05 this time) But I guess I know now? It's washer fluid perhaps mixed into the orangeish coolant.

Help!! I am really confused and concerned and in all my searching I have found no one else with this problem.

 

Well we found the source of the coolant issue. The heating coil in the washer fluid reservoir failed. The thermostat (?) at the bottom of the coil had burst apart and so the heated coolant was flowing freely into the reservoir. For the time being we have reassembled the pieces and put some JB Weld on it until I can find a replacement part, which is hard to do when you don't even know what it is called. I guess a trip to the dealer is in order. My other option is to bypass the heating element but as I live in Colorado, I'm thinking that's not such a good idea.

Now I have to find out why the fans aren't coming on.

 

This exactly why MB wants you to use a MB specific coolant. It is designed NOT to corrode any part of the coolant system. Use ONLY MB coolant unless you really know your coolants in order to pick an alternative.

Note: you need to flush and renew your coolant system after you fix your reservoir problem.

 

Well I have now replaced most of the cooling system hoses, parts etc. I have bypassed the washer fluid heater and removed it from the reservoir as the JB Weld held for only about 20 miles. I have repaired the reservoir (cracked from heat) and no longer have any coolant leaks that can be seen or smelled!!

The auxilliary fans are still not coming on properly. I replaced the blue temp sensor/switch that controls the A/C and the fans but it still isn't working properly. Does anyone know what that sensor/switch is called? I am not sure that I ordered the right part. It's pretty tough to find. When I bypass the sensor and direct connect the sensor wires the fans come on at high whenever the key is on and of course the A/C doesn't work. When I connect to the sensor, the A/C works but the fans don't come on no matter how hot the engine gets, except when the cooling system is actually turned on, then they come on at low and the car gets too hot. Does anyone know what could be causing this issue?

Thanks!