W166, ML350 Bluetec. Coolant loss after a recent water pump change.

[ketapa]

Hi everyone!
I'm new here and new to MB ownership, too (about 10 days post purchase of a 2014 ML350). I was hoping to get some advice on a coolant leak - I recently saw the low coolant indicator light come on and assumed this may be due to the recent water pump change my car had, so bought 5L of MB-approved coolant and topped it up (maybe 300-400ml, if I had to guess). Well, I had the same indicator light up again yesterday, and when I checked the coolant level, it was indeed lower, with a hotter engine, too (I topped it up when it was completely cooled). Not a substantial amount of coolant lost, but I did have to top it up again, so some of it was certainly gone.

I have bought some fluorescent dye to put through it, but my concern is that it might be an internal leak - since I bought the car it had a slightly off sweet scent, which I assumed was just leftover from the detail the dealer had on the car pre-sale, but while it has gotten a bit more faint, it's definitely there and I'm worried it may actually be a slow coolant leak in the HVAC system.

Has anyone come across any similar issues? I haven't tried to look for leaks as I spilled a small amount of coolant when topping up yesterday so it would have been difficult to distinguish a fresh leak from my minor spillage (I used gloves and cleaned what I could reach).

 

[MSG2004]

Could it just be air?
Mine dropped several months after buying my brand new gle in 2016. MB had a good look and they found nothing and topped it up it was ok.
Two things come to mind re your car - air in the sytem lowering coolant or fault water pump/gasket are the main areas I'd look out for. However, in an older car, pipes can crack etc and just a coincidence you changed water pump.

 

[ketapa]

Good point! I'll ask MB to pressure test it as I'm bringing it in for a recall on 03/01, so hopefully will find out then.
For anyone landing on this thread by accident, I've also picked up some fluorescent dye and a UV torch (grand total of £15 off amazon) and will check that if the pressure test doesn't find a leak but I keep loosing coolant.

 

[ketapa]

Update, I was told to bleed the cooling system before assuming it's a leak, in case the garage that changed the water pump didn't do it and that air in it trapped during that change could be the reason for the coolant level dips.
Good the engine running and heating on max, but noticed this very small foaming - is that air escaping? I know if it was a HGF the foam would be much thicker and potentially darker, so wondering whether this is an indication of anything at all. Getting it pressure tested tomorrow, but it read about someone that had a similar coolant light come up that turned out to just be air after a pump change.

 

[MSG2004]

I've never noted foaming in my coolant or any of the childrens cars but I've not rally looked at the coolants for years.
Get it pressure tested, possibly head gasket leak etc, but I'm no mechanic.

If it was not for the foaming, I would have though as per my intial post here, ie air in the system. It may still be that but you are getting it checked, so
good luck