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Discussion Starter #1
Over the last couple of months I have been losing coolant in small quantities. The coolant light comes on roughly every 250 miles driven (I then top up the coolant and drive again and coolant light goes away). I am currently topping up using a generic coolant - it says it is suitable for all engines.

At the bottom of the radiator, on the undershield tray, they are small drops of coolant. I had the radiator pressure tested with 100 lbs of pressure and there were no leaks that could be identified either from the radiator or the pipes. I presume the drops of coolant are from the overflow pipe.

I did a search and this post: http://www.slkworld.com/slk-r170-general-discussion/11313-coolant-level-light-coming.html says that it could be:

1) Wrong coolant - (MB service book does not state a coolant type or even that you must use MB coolant)
2) Faulty thermostat
3) Low windscreen wash fluid (is this really true & how would this trip the coolant light???)
4) Oxygen sensor and Air Mass Sensor (although the guy said this only happened when the CEL came on after topping up the coolant).

If it is a faulty thermostat, how can this be checked? Would a MB diagnostic test show what needs replacing? Air Mass sensor / thermostat etc.

My car: 2001 R170 200k and has covered only 26k miles.
 

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Are the pipes in good condition? On a previous car, I had a similar problem caused by old cracked pipes that apparently were loosing water by evaporation. But you say your car has only 26k miles and the car I'm talking about had much more than that!
 

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Thanks guys. I just hope it isn't the dreaded head gasket... is there a simple test (apart from using an oil spectrometer) like smelling the coolant or anything else?

ETA: I've taken it to my local mechanic a few weeks back who originally said it probably isn't the head gasket as the pipe from the coolant to the engine hasn't gone rock solid or hasn't become bloated.

Arghhh. I will post the solution should I identify exactly what it is.
 

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hi, i have recently discovered the same problem on my gf's 98 slk230..i found out that hers was also losing coolant at a faster rate. i found that the radiator cap was not holding the pressure from the tank. i switched that out and never had a problem since. let me know if it works!
 

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hi, i have recently discovered the same problem on my gf's 98 slk230..i found out that hers was also losing coolant at a faster rate. i found that the radiator cap was not holding the pressure from the tank. i switched that out and never had a problem since. let me know if it works!
Cheers for the info. I have double checked that the radiator cap is sitting tightly and correctly...

My main concern is that there are definitely drops of coolant on the under shield tray below the radiator... as i mentioned in the OP, these drops I believe are coming from the overflow pipe (I might be wrong). What I am very concerned about is that I hope it is not the head gasket.

It just seems losing coolant can be attributed to almost anything... unsecure radiator cap, wrong coolant, faulty o2 sensor, head gasket, faulty thermostat... the list just goes on. Evaporation of water through the pipes is the best one I've heard so far!
 

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Discussion Starter #7
A bit more searching and it seems the water pump is a common failure as well, so add that to the list. I am taking it to another indie merc specialist who hopefully will be able to find the fault.
 

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Cheers for the info. I have double checked that the radiator cap is sitting tightly and correctly...

My main concern is that there are definitely drops of coolant on the under shield tray below the radiator... as i mentioned in the OP, these drops I believe are coming from the overflow pipe (I might be wrong). What I am very concerned about is that I hope it is not the head gasket.

It just seems losing coolant can be attributed to almost anything... unsecure radiator cap, wrong coolant, faulty o2 sensor, head gasket, faulty thermostat... the list just goes on. Evaporation of water through the pipes is the best one I've heard so far!
when i checked out the radiator cap, it looked secured also, but double check the spring on the cap. the excess coolant on her car was also coming from the overflow pipe.
 

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any news yet type-r?, my coolant check light also switched on the other day on a medium journey uphill (from the dead sea up to the capital Amman) its a series of bends and is slightly inclined all the way. i kept my eye on the heat gauge and the temp didn't change, i checked the radiator and noticed the buoy to be floating so i guess no top-up needed. Washer fluid is sharing the radiator coolant? or both sensors are connected to the same check light? "Squeaks" (my car SLK03 200 KOMP) is definitely trying to say something but I'm not sure what it is. I'm gonna start making a list of possibilities so that the garage would check them rather than their usually uneventful check-ups they usually do.
 

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Mine is doing the same, I checked the level and seems to be fine. Only thing I have been able to troubleshoot is the ambient air temp. seems to only come on above 70F/21C.
 

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More than likely, it's the water pump. Here's why:

If it were a hose, the "drip" would become a pressure stream after a day or two.

If it were a head gasket or cracked head, the water would be going INTO the motor and mix with the oil to make a milky looking oil. The car would also over heat pretty quickly.

It could be the cap, but once again, you should see steam coming out of it when hot.

Water pumps do not last forever. The seals and bearing eventually wear out.

Until you can replace the pump, put in some "Bars leak". The stuff will close up small holes for a while. There's also "Alumiseal" which does same thing but works better on radiators.
 

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On mine it is just the light, doesn't appear that I am losing any fluid. I just replaced the IC pump for the supercharger and topped off the fluid. Hills seem to effect it as well.
 

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Discussion Starter #13
any news yet type-r?, my coolant check light also switched on the other day on a medium journey uphill (from the dead sea up to the capital Amman) its a series of bends and is slightly inclined all the way.
Ermm, there is no easy way to say this but..... I think I have been mistaking the Check Engine Light for the Coolant light!!! :( At least, the CEL came on the other day and I used a diagnostic tool to read off the code. I will post my results of that fix soon but sorry, it seems like I completely went up the wrong alley with the original light. I think the coolant spots originally threw me but I am pretty confident that was just from the overflow pipe.
 

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Discussion Starter #14
PS, I agree with Todd's assessment too. When I took my car to an Indie specialist explaining about my now phantom coolant leak he said it is almost 90% the water pump as he said it was an extremely common problem. You can actually see the waterpump from the engine bay and if look closely you can see any drips or water mark indications on the pump itself.
 

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I figured out my coolant light issue, the radiator fan was unplugged. MB did it when they tested the IC pump :soap:, and never plugged it back in. So check your fan and make sure it is working.
 
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