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Matt, Mechanical Engineer
Category: Mercedes
Satisfied Customers: 23982
Experience:  BEng hons Mech engineering, in auto industry 22 years
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Thank you the Water level is dropping enough for the warning

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Hi pearl thank you the Water level is dropping enough for the warning light to come on and the local mechanics have run it all day and there is no sign of a leak what could be the problem?
Assistant: What part of the car is the leak coming from? And are you sure it's water?
Customer: We don't know when I drive it the coolant level drops steadily but it is getting worse no visible sighting of where the leak is
Assistant: What is the model/year of your Mercedes?
Customer: Cd110 2012
Assistant: Are you fixing your vehicle yourself? What have you tried so far?
Customer: No a local garage is trying to find the problem they have run the van all day today and the coolant level has not dropped so it is only happening when the vehicle is being driven
Assistant: Anything else you want the mechanic to know before I connect you?
Customer: The problem is getting worse every day yesterday I filled the water up to max and after 3 hours driving the water level had dropped out of sight the reservoir was emptyi


If you have a tiny pinhole leak in a radiator then these often don't leak water but will lose water as steam ( steam molecules being small enough to pass through the hole where liquid cannot) take a look on the rad for any signs of localised corrosion and for areas that look like they've been 'steam cleaned'.

If all of this is OK it may be worth replacing the header tank cap as again you can lose coolant as steam if this is blowing off too early ( the cap should hold pressure of around 1Bar)

The other thing to try is a head gasket / block test kit as these take a coolant sample and analyse it for any signs of combustion gas - if present this would indicate the head gasket is on its way out

and as a fix for internal leaks I’ve found this product works very well, without clogging heater matrixe’s

it doesn’t last forever though

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