I have been topping my x5 e53 4.4i 2005 coolent up with tap water and have just discovered recently thisis a no no due to the deposites. The first time I did it the bmw guy on the phone said to just use tap water. I can’t believe I didn’t investigate this earlier! Now I hope I haven’t stuffed something up with the deposites.

For the past 6 months I have been topping up with tap water. Lately, it has been 2L lots and now I have found the leak to fix. I know, extremely lazy on me not to address this earlier. So, I hope I haven’t damaged anything.

Waiting on delivery of coolent expansion tank to fix leak then I will get it flushed and new coolent. But what to do till then? I was thinking of buying some coolent (VALVOLINE Zerex G-48 RTU 20L) already mixed and top it up with that or even get some bmw coolent and mix. I am definately going to get some demineralised water. I just hope I haven’t stuffed the engine! Ahhhh....so frustrating that I did’t investigate first like I usually do.

I only hope I have a little of the original coolent in there and it hasn’t been expelled.