Any size leak is potentially a big issue, I'd check it closely and if it goes down at all get a pro to find the leak. Fluorescent dye can be used to help find it. Is it under warranty, did you have the coolant changed? One thing you can look at is the motor oil, a leak into the oil will turn oil whiteish. No it's not normal to loose really any coolant, it's a sealed system. And leaks just get worse.

 

If you have blue coolant, don't use Zerek G-05 (yellow).

I believe blue is G-48. Just get genuine MB, it's not that much more.

 

Thank you guys, I've decided I'm taking Archie in today to get checked. I'd rather pay a little bit of money for them to check it out and fix whatever they need to fix than mess with it and have it be double or triple the price in damages...
Thanks for the help/advice!

 

I've decided I'm taking Archie in today to get checked.

It is most likely natural evaporation. I just had to top off my wifes GLK when the weather got cooler.

While you are there, buy a jug of coolant at the parts counter. It's good to have on hand. Remember to mix 50/50 with distilled water.

 

I agree with others on only using MB Coolant, formulas are determined for the specific metals and sealants a manufacturer uses. I would not trust a big parts store to really know what specifics MB coolant is, and I just wouldn't trust off brands. If you didn't take it in just monitor the level awhile.

 

It is most likely natural evaporation.

It's a closed system, not exposed to atmosphere, so there's no opportunity for evaporation. If coolant level drops, it should be only once, associated with a big drop in ambient temperature, and only by a small amount.

Anything more than this indicates a leak, and the leak may not result in coolant on the garage floor. It could be leaking past a head gasket into the combustion chamber and get burnt off. A small leak onto a hot engine block can burn off too, and not make it to the ground.

My wife told me she had a low coolant warning come up. 2015 GLK250. When I checked it, I added 300mL of coolant to get the level sensor to clear. I could smell coolant in the engine compartment but couldn't see the leak. It was due to a failing coolant pump and thermostat gasket.

 

It's a closed system, not exposed to atmosphere, so there's no opportunity for evaporation.

I beg to differ. Yes, it is a closed system, but it is not a sealed system like the A/C loop. There is indeed a gas exchange with the atmosphere, slight as it may be, due to the expansion and contraction of the coolant. Otherwise it would be factory pressurized with a pressure tank of some sorts (like a boiler loop) and stay pressurized forever like your A/C loop...which it is not.

There are other factors to consider as well before declaring it must be a leak. We don't know what the original coolant level was as the OP admits to "knowing nothing about cars" and most likely never checked it. It could have been borderline for some time.

That being said, the key is to look for a continual loss. As they say "Once a fluke, Twice a trend". [emoji38]


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Settle down Francis. [emoji38]

Your vehicle isn't "pissing on your driveway" because you have head space, air (a gas!) in your pressurized coolant recovery tank unlike the radiators of old. During times of heavy load, for example a long drive, uphill, on a hot summer day, it is possible the coolant could expand enough to make the reservoir cap vent some of this air. Then as the engine cools down later, creating a vacuum, that air is replaced. Hence an exchange of gasses.

Not sure why you are picking a fight here, I was simply giving the OP a potential explanation. Not the ONLY explanation. Geez, every time you open the cap you have a gas exchange, so your comment that there is "no opportunity for evaporation" isn't exactly true. Limited? Sure! But not zero as in a true, sealed system.

I will reiterate that the whole assumption is potentially flawed as we don't know what the starting level was. The OP looked and saw it wasn't at the "Full" mark, that's all we know for certain. Hell, for all we know it's been at that level for years without moving. Maybe it was a bad fill at the factory. Maybe a prior tech did some work and didn't top it off. Who knows!

I tend to be a bit more conservative before declaring disaster. As I said previously, a continuous loss would certainly indicate a leak. In my humble opinion if the OP tops it off and it remains topped off, it's nothing to be concerned about. If however it continues to drop, then of course that coolant is going somewhere and the leak needs to be found and fixed. I would suggest doing this simple test before chasing a leak that may not even be a leak.


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If the level is less than an inch below the full mark, I'd simply add some distilled water and keep an eye on it. If it continues to drop, then it's time to diagnose the cause.

 

Thank you for saying what I've been saying....in many less words. [emoji38]


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