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[Solved] Mercedes C180 Low Coolant


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Hi Scotty, 

My dad has 2013 Mercedes benz C180 with the 1.6L 4 cylinder turbo engine. He is the original owner from New 

it has been serviced every 7000 miles with full synthetic oil.

Recently it has Developed a problem where the coolant warning light comes on when the car is left overnight. 

it is not losing coolant as I've checked and the radiator is up the full mark. The car runs perfectly fine it doesn't over heat & the temp gauge stays in the middle all the time. the light only comes on first thing when we start the car after it has been sitting for a long time. 

Could it be a weak battery? As I have checked most other things including the head gasket test and nothing show up. and the coolant is fairly new it was changed in 2019.   

5 Answers

1. As a Mercedes owner I can confirm that a weak battery can generate all sorts of electronic problems / errors in these cars, since the car is full of electronic modules of different sorts, and if a car battery cannot give them enough power for their startup (and a weak battery cannot, since at startup it will be giving all it can give to the starter), they cannot boot up properly and may be glitching till next startup or even till next full reset (or error codes erasure).

This is however easy to check: buy or borrow or take a jumpstarter (in one of Mr. Kilmers videos he recommended some), and one of these mornings try starting the cold engine with the help of a jumpstarter. If the coolant lamp problem goes away, then it is definitely the weak battery. You may however still want to live with it as long, as it is cranking your car allright. The later you buy a new battery, the longer it will last 😉

2. But first of all make sure you really checked the coolant level in the expansion reservoir, and not somewhere else. You want to check it cold, and it has to be exactly at the "Cold Level" mark, while the car shall be standing strictly horizontally. Also make sure that what you see is really the coolant level, and not, say, a mark left on the inside walls of the reservoir by old dirty coolant which is no more there. Ive seen cars in which it was not that easy to tell... Since if what you see is a residue mark from old coolant, your real fresh coolant level could be anywhere - for example, at the very bottom of the reservoir and not visible at all. It might be even below the coolant lamp sensor when cold, causing the lamp to engage at startup, only getting higher as the coolant expands as the engine gets warm... Just a thought.


Maybe the coolant level sensor isn't in the radiator. Maybe it's in the reservoir.


Mercedes put a coolant level sensor on the back side of the reservoir tank.  It's on the driver's side.  If this sensor goes bad, you have to replace the reservoir tank assembly as the sensor is built in.  Check the wiring and the plastic, snap on connector at the tank to make sure it's on good condition and properly connected.


You could check the battery but I doubt if it's that more often it's electronic failure it shouldn't come out with the engine turned off. So for some reason it's still getting power and turning itself on could be real stinker tracing that one down good luck on that

Hi Scotty, I had the battery load tested by an independent guy who specializes in Mercedes Benz.
It turned out to be Bad Battery which was only producing 445 CCA instead of the 800 CCA it was rated for. it was also only producing 11.5 volts. The guy who tested it said that on these newer Mercedes a weak battery can trigger all sorts of different warning lights on start up as the computer modules don't get the required voltage until after the engine starts and has been running for 30secs the lights will go out that usually means a dead battery.


3. And one more thought: if your battery delivers 445 CCA instead of the 800 CCA when charged to (only) 11.5 Volts (which is around the lowest battery voltage I have seen on my cars - the voltage at which my batteries are hardly able to crank anything, especially in cold weather) - maybe the battery is not that bad: maybe it is simply undercharged (being regularily not charged enough) due to your dad not driving his car enough? Could be as simple as that. Just charge the battery to its full voltage and re-test.

I have had the battery tested by an independent Mercedes Benz tech it was the original 2013 battery & it was not holding charge during the test so we replaced it. I have checked the coolant reservoir and it is definitely full. I have also pressure tested the cooling system and there are no leaks to be found it is holding pressure no problems at all. so far after driving 100 miles no lights have come on and I had all the codes cleared as well.

"the original 2013 battery"
8 years for a car battery is a long life, so no surprise that it deceased.