I currently am experiencing a weird problem.

When I fill my coolant reservoir to the MAX limit, any time from about 1 to 3 days my car leaks antifreeze near the wheel well but I could not see where it was coming from. The car does not overheat. when the level goes down it does not pass the coolant sensor , except intermittently if i turn a corner or go up a steep incline?!?!? I am quite puzzled and appreciate any help. The car is a 1986 560 SEL just turned 140K miles. My Behr radiator is 1 year old so i don't think its the problem. I inspected my hoses to/from expansion tank to radiator and have found no problems. I also removed the expansion tank and found no cracks etc. I also replaced the radiator expansion tank cap. Could this be leaking through the sensor?????Thanks all!!

If there is no visible sign of leakage, you'll need to peform a cooling system pressure test. Auto Zone and other mass marketers rent such a device.

Check the search facility - has been discussed many times.

Just thought I would post an update.
I ended up finding the problem. The hose was in 2 pieces to my overflow reservoir. You know the one in the wheel well. It was like the person that had it before me replaced the hose from the expansion tank and just pushed the hose through the hole. They aren't even the same size.

While doing this and testing it, My car still got hot. I then started to hear a hiss and leak ... There was a crack in the seam in the expansion tank right below where the hose fits to goto the overflow reservoir. I hope this helps out someone, cuz it was a pain in the ass for me. The crack was never an issue except here in the AZ summer where ambient temps are 110-115 lately.

AFAIK the reservoir overflow hose just goes into that hole with nothing at the other end. That's how it is in the 300SD and 300SE. I've never looked at the 300SDL hose because the air cleaner kinda hides the hose. I can't imagine it's different in a 560SEL.

There was a crack at the bottom of the tank of the 300SD. A quick RTV patch seems to be holding. FWIW, the SD runs at a lower system pressure than the other cars if the cap rating is any indication.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD

FYI,

In the 560SEL there is in fact 2 expansion tanks. There is one above the left passenger tire w/rad cap on it, and another overflow reservoir in the wheel well. It can only be seen if the inner liner is removed with about 10 bolts. I ended up ordering a new expansion tank from fastlane, just because it's so damn hot here in Arizona.!!!



R@Z

Time to check for a second overflow tank in the SD and SDL...

FWIW, the SDL outside temp gauge reads 136F pretty much all the time... in San Jose, CA

Thanks,
Sixto
95 S420
91 300SE
87 300SDL
83 300SD

Just wanted to post my last update. I replaced the expansion tank, new oring for coolant sensor, new temp switch, and replaced the hose from the expansion tank to the overflow reservoir. Drove to work today with ambient temps around 112F and the temp never rose above 100C. It stayed mostly between 80-100(pretty much horizontal.)

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R@Z()R

1986 560 SEL