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'01 SLK 230
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Discussion Starter #1
Hi,

My low coolant light started coming on after about 10 minutes of highway driving, so I checked the level and it was a bit low (the expansion tank was about half full and the float inside wasn't all the way to the top). I filled it and now the coolant light is off, but the question is, where did the fluid go? As I understand, there are 3 possibilities:

- Faulty radiator cap allowing some fluid to escape through the overflow tube.

- Leaky hoses. I found no evidence of any leaks, however.

- Head gasket :(

I really hope it's not the last one! Is there any way to identify which of the three? There's no white smoke in the exhaust or anything like that - the car runs perfectly.

Thanks,
cinergi
 

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2002 SLK 230 1986 560SL 2008 Honda CRV
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Look for sings of leaks under the car, check the dipstick for signs of a white milky goo, remove the oil fill cap and look for the same white goo.
 

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Likely hood is a radiator cap, a inspection after lower cover removal is an excellent idea. Using a pressure tester with engine cols is a much better idea but if no traces of white colored crusty liquid are noted the cap is likely. Head gasket problems in that car are unusual.
Bill
 

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02 - 32 (Stock); 99 SLK230 (RIP); 81 CJ7 (Fully MOD)
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399 Posts
There is a float under the radiator cap.
If this is not seat properly even if you fill up, your coolant light will be on :D
So, make sure it's filled up and the float (white bobbin) sits properly :rolleyes::thumbsup:
 

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99 slk230 sport
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if its been a few years it can be low just from "cosmic evaporation". but look for wet spots, smell the tailpipe after starting the engine, a coolant will smell sweet back there, and check the oil for mocha, and check around the water pump if possible, as this is where the seal will fail either on the shaft, or gasket to engine, and it will weep very very slowly, so you might not see a spot on the ground as a result (this is a general car system theory, not positive it applies to the slk as i have not been down that road yet). otherwise dont worry.

oh ya the heater core can leak too, and it can be pooling in a weird area sometimes, and difficult to see as the unit is obstructed by firewall or other stuff. not sure what possible consumption theintercooler system could pose, but theres another pump, and heat exchanger with hoses and such that could leak, if it is internal to the intercooler then the coolant would be pooling in the intake pipe and minght get sucked into the engine that way, which could cause intermittent burning? just thinking out loud.
 

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It may or may not be related, but I had the same problem...coolant level light would come on sporadically. I checked the level, seemed okay but I added a little coolant...still came on. Finally I took it to the MBZ dealer and they replaced the sensor...a couple of months later it started coming on again.

After a few months of this I found out here that it was the windshield washer fluid that was low. It turns out that they share the same circuit. Brilliant. :rolleyes: I keep the washer fulid filled now and haven't seen the low coolant level light since.

That may or may not be the issue...but if you don't have any leaks and everything appears normal (except for the idiot light) you might have a look at your washer fluid level. Here are a couple of threads on the subject:

http://www.benzworld.org/forums/r170-slk-class/1363405-coolant-level-sensor.html and
http://www.benzworld.org/forums/r170-slk-class/1303991-coolant-washer-level-lights.html
 

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'01 SLK 230
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Discussion Starter #8
Thanks to all who replied! I'll check the oil and smell the tailpipe as suggested. I've already looked for leaks at the hoses, reservoir, etc., but couldn't find any. Nothing on the floor either (I check this regularly even when there's nothing wrong :).

richsadams - The washer fluid is actually the first thing I checked, since I remembered reading a thread about it on here. It was indeed low, but that wasn't the problem (the coolant light kept coming on). It hasn't come on since I filled up the coolant, so far so good...

Last time I changed the coolant was in October 2006, so it's possible that it's just normal evaporation as berk suggested. I'll change it again in October of this year (every 3 years).

I'll post any new developments!

Thanks,
cinergi
 

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Hi,

My low coolant light started coming on after about 10 minutes of highway driving, so I checked the level and it was a bit low (the expansion tank was about half full and the float inside wasn't all the way to the top). I filled it and now the coolant light is off, but the question is, where did the fluid go? As I understand, there are 3 possibilities:

- Faulty radiator cap allowing some fluid to escape through the overflow tube.

- Leaky hoses. I found no evidence of any leaks, however.

- Head gasket :(

I really hope it's not the last one! Is there any way to identify which of the three? There's no white smoke in the exhaust or anything like that - the car runs perfectly.

Thanks,
cinergi
Hello! I joined the forum, because i have had a simmilar problem with the cooling level light coming on, on my E 280 cdi 2006, thus the expansion tank was full. I checked the forum and did not find any answer that could work, so i replaced the sensor with an original one, and still the same. Also the MB dealership did not find the problem, but then we dismanteled the coolant tank and washed it wit soap and water, no one of the senior nechanics did not know that in the tank (around the sensor neadle) because the sensor alone is dry (actually not submerged in coolant althou it looks like) is a floating magnetic ring, which is submerged and schould be mowing up and down aroud the needle, this changes the resistence in the needle and so you get the readig. But that fliating ring was stuck on the lowest position dur to filth wich accumulated over the years (allthou coolant changes were done) and with washing the expansion tank and rrinstalling it, the problem was solved! Hope it helps!
 

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2001 SLK320 ex Japan.
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261 Posts
Hello! I joined the forum, because i have had a simmilar problem with the cooling level light coming on, on my E 280 cdi 2006, thus the expansion tank was full. I checked the forum and did not find any answer that could work, so i replaced the sensor with an original one, and still the same. Also the MB dealership did not find the problem, but then we dismanteled the coolant tank and washed it wit soap and water, no one of the senior nechanics did not know that in the tank (around the sensor neadle) because the sensor alone is dry (actually not submerged in coolant althou it looks like) is a floating magnetic ring, which is submerged and schould be mowing up and down aroud the needle, this changes the resistence in the needle and so you get the readig. But that fliating ring was stuck on the lowest position dur to filth wich accumulated over the years (allthou coolant changes were done) and with washing the expansion tank and rrinstalling it, the problem was solved! Hope it helps!
Yup. That happens.
 
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