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Discussion Starter #1
Hello SLK'ers,

I'm just shy of 107k miles and 11 years old, but I still love Betsy! A few rattles, and a sluggish roof but otherwise she's aging well.

I need some help with a Dummy light. Let me explain.

I blew a rear tire last week, and as some of you know I'm not the most mechanically inclined person, so it took me north of 90 minutes to figure out how to change the tire. I have swapped tires before last Christmas so I had a decent idea of what to do; but its lots different at 6am in the morning in 25F weather dressed in executive office attire on the side of a major interstate off-ramp. Unfortunately I learned too late that my Spare Tire kit did not have the donut lug nuts! I was simply furious over that. When I tried to call MB customer service they were closed.

Thankfully, the lug nuts from my winter tires fit perfectly and my wife was only 15 minutes away so I called in reinforcements and got to a tire store with the doughnut secure to get those winter tires installed.

At my next service, I plan to complain to MB and see if I can get a spare set of lug nuts for the donut.

During the 90 minutes a big portion of time I spent sitting on my car warming up and reading the manual. I confess it’s been a while since reading. I had a dummy light coming on rarely and I noticed that the manual doesn’t appear to have an icon legend for the dummy lights so it’s difficult to know which light means what. Do we have a pictorial explanation of which dummy light does what? The light that comes on rarely is a yellow one, which looks like a box with a bit of water in it. I suspected it was the windshield wiper fluid as I added about 3/4th of a gallon that morning after the blown tire, and the dummy light hasn’t come on since. I did check the radiator and that fluid was at the top, and using that little device with colored balls, it tested at the right amount of anti-freeze. I couldn't think of any other box with water in it except perhaps the battery but I don't know how to test that. Its about 4 years old, and the car is running exceptionally well so I doubt the battery is a concern.

Thoughts welcomed on that picture legend for the dummy lights...

Thanks,
Douglas
 

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Discussion Starter #3
It was the Low engine coolant level warning lamp. Interesting. It only comes on very briefly, and maybe only once a day for the last 2-3 weeks. It turns off after just seconds.

My father was telling me about radiators having an overflow tank... but, I don't seem to see anything other then what is just below the radiator cap. I just came back from lunch and verified my radiator is full again. The float is at the top. The liquid inside is pretty clear with just a slight oily feeling sort of like a cola I'd call normal (though I'm not an expert.

Cheers for the quick response.....
 

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2001 SLK 320(217K Miles), 2002 E320 Special Edition(183K Miles)
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You have a donut spare??
My slk 32 doesnt....
A
SLK230 & SLK320 has 16 inch rims and a spare. The SLK32 has 17 inch rims and no space in the wheel well for a 17 inch spare.
 

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2001 SLK 320(217K Miles), 2002 E320 Special Edition(183K Miles)
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Regarding the dummy lights - due the the way the wiring is done for the radiator level and the windshield reservoir (one common wire with different resistors) it is quite common for a low windshield reservoir level to trigger erroneously the low radiator level light. Fortunately I've never heard about the reverse, since you are more likely to act on low radiator than on low washer reservoir.
So if the radiator level light comes on and the radiator level is fine (like in your case), just refill the washer reservoir and see if that solves the problem.
 

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1998 SLK 230
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2,648 Posts
pretty common issue...

its unlikely to be the coolant level sensor as it is not submerged in fluid... the common cause is the windscreen wiper fluid level sensor which is actually in the washer tank.

reason why it fails is the seal at the top of the sensor degrades over time letting water into the sensor. this causes the resistor inside and the reed switch to corrode and then eventually cause an open circuit = throwing the light on always.

easy to fix if can be bothered taking it apart will cost few dollars to fix.
Bazzle has DIY here too...

x1 180 Ohm resistor $0.10 or less
x1 Normally open magnetic reed switch about $1-$2

they are wired in parallel.. if water level is ok circuit will read 180ohm... once the magnet in the float gets low and close to the bottom it trips the reed switch and then the circuit goes to 0 ohm.

when closing up the sensor after repair seal it with a good silicone and it will never happen again.

if you cant be bothered the part is about $95AUD at the dealership here in OZ. so it isnt cheap for what it does!
 

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Two 1998 SLK230s, 2003 SLK230 SE, 2002 ML320
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+1 what Subby said. It's a common problem and I have had this issue attended to several times. The last time the light came on when it was particularly cold (for Australia) and I suspect the contraction of the conductors in the washer bottle sensor may cause it to go open circuit and switch on the light.
 

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Discussion Starter #10
Hey SLK'ers, thanks a ton for the special attention. I may have some good news. Like a dummy I found the windshield wiper fluid reservoir lid wasn't tightly attached. It snaps on. At lunch yesterday I added another half-gallon, after about 3/4 of a gallon on Sunday. I don't know how much this is supposed to hold, but, while adding the half-gallon I had a bit running out onto the floor. And my drive home yesterday, and drive into the office today I didn't get any dummy lights; which gives credibility to the assertion that the sensor may be tripping related to the windshield wiper fluid. Great idea everyone. I wonder if having the lid loose on the fluid may have done something odd with pressure causing the dummy light to trigger briefly at times.

To answer the previous question about the spare donut, I have 17 inch wheels on the SLK230 with the Sports package on the rear; but, it has a 16 inch donut spare in the trunk. I recall that in 99 and 00 there were discussions of a 'conversion' kit basically where a can of some kind of tire spray was used to replace the donut. I personally prefer the donut -- my tire was shredded and no amount of compressed magic could have saved the tire. The tire guy at Discount Tire said that I picked up a nail that caused the tire to deflate and I drove at least 3 miles (as many as 8, I'm not sure) and the metal of the wheel shredded the rubber. They measured the wheel and confirmed it didn't get bent so I didn't drive far on it.

Thanks,
Douglas
 
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