In the last few days the "low coolant" light has been intermittently turning on on my friend's BMW X3 (2007 ~70K miles). The light is not constantly on yet.

I checked the coolant reservoir and float stick was slightly below the "low line". Nevertheless, the float stick was still floating and there was still some fluid left inside the reservoir.

Peek inside the coolant reservoir

I would be inclined to buy and pour in new coolant, however, after googling around I have few doubts now:

  1. She got engine gasket replaced outside BMW a year ago. Does this kind of job imply also coolant change? if so, then I guess there is possibility that it is not the blue BMW coolant in her car anymore and in this case the coolant should be flushed if its type can't be determined anymore?

  2. If coolant reservoir is not completely empty and low coolant light is turning on only intermittently, is it ok to drive around for a day or so for short trips until this gets properly fixed?

  3. If it is better not to drive around in current condition, can I simply pour in a liter of distilled water to get the car around for a day or so? I guess this would dillute the water:coolant ratio from 50:50 to something like 60:40.

  4. I suppose it is also important to find out why coolant has disappeared. I guess there are three possibilities:

    • coolant is leaking in oil compartment (in this case the oil may become milky)

    • the coolant is pouring on the street (in this case there could be something dipping below the car)

    • coolant gets burned together with fuel and goes out through exhaust pipe (not sure what hints are for this case).

    Are the any possible root causes that could explain why coolant disappears?

    I am attaching following picture that may provide more hints, because there is fluid exhausted with force from what I think is radiator hose:

    Suspected radiator hose

  • 1
    Wow, you are drastically overthinking this. If it's low on coolant, top it off with the proper mix. Done. If the problem occurs again, have it checked for leaks.
    – cory
    Dec 6, 2016 at 20:31
  • 1
    @cory Well, the internet says that one needs to be careful with mixing different coolants, because you may end up with Jelly in cooling system. Assuming that outcomes like these are possible, I think the rest of questions become even more important. Dec 6, 2016 at 21:00
  • Having a similar problem. What ever happened with your coolant situation?
    – Jeff Neill
    Jan 25, 2017 at 18:18
  • @JeffNeill I first filled up the tank 1 liter of distilled water to get the light off. Drove for like 100 miles. Then in few days filled up another 1 liter of BMW gray coolant. Beware and don't buy the wrong coolant! haven't had any issues since then. Apr 17, 2017 at 5:04

5 Answers 5


A few thoughts:

  • In a pinch, any coolant is better than no coolant

    Even litigation-wary vehicle manufacturers will invariably recommend this in owner manuals (paraphrased from my W12 Touareg manual):

    If the recommended coolant/coolant grade is not available and the coolant level is low, top up the reservoir with distilled water and have the system evaluated by an authorized dealership as soon as possible.

    The reason for this should be obvious, but the consequences of engine damage from overheating is far worse than any impact of using the wrong fluid on the cooling system.

  • Coolant evaporates and leaves a milky-white stain behind; that's oil on the radiator hose

    Given the oil filter housing is in the nearby vicinity I wouldn't be surprised if the stains are the remnants of a recent oil filter change.

    If the oil hasn't been changed recently, there may be a leak associated with the neighboring oil cooler or a crack in the oil filter housing. The power steering reservoir is also a possible culprit.

    I'd recommend cleaning the oil spots and monitoring to see if the stains return in the short term.

  • Coolant type can matter

    Given that the coolant is blue, it could be that the cooling system has been adversely affected by the use of a coolant type it wasn't designed for, though I'm not sure if I would blame it for this vehicle's coolant loss woes.


Very simple

Fill up the coolant!

All the symptoms tell me that the coolant is low. Fill it up! 99.9% chance that will fix your problem entirely. If it doesn't fix the problem, post up, and we'll try to help you diagnose it. But almost certainly, filling up the coolant will cure your issues completely.

  • Should I flush out the old coolant before filling in the new one? is there a chance that after gasket replacement the maintenance guys poured in Dexcool (or some other coolant that is not compatible with the "regular" Green One)? Dec 6, 2016 at 23:19
  • 1
    You're right, you can't be certain of what type of coolant is in there. I would recommend using distilled water like you mentioned to see if the level drops again. The amount you add will likely be negligible considering how much the entire engine uses so the ratio shouldn't change too much. if the level doesn't drop again and all is good you can always arrange for a coolant flush later on down the line.
    – atraudes
    Dec 7, 2016 at 0:35

I would suggest topping it up with water to start with - the slight dilution shouldn't make too much difference unless you're in an area with very cold weather. Keep an eye on it to make sure that the level doesn't drop again, and get it flushed and replaced properly fairly soon, if you can't determine whether it has the correct coolant in or not (remember to dispose of the old coolant responsibly, as it's toxic to animals)


What's the weather been like on the days when you saw the Low Coolant light?

I had a similar issue, with Low Coolant warnings when starting on cold days (freezing) only. The coolant contracts when it gets cold, and the coolant level would be marginal on cold days. After 30 seconds, the warning would go away.


Judging from the picture of the coolant tank with cap off, you have oil mixing with coolant as evidenced by the sludge visible. My X3 did the same thing. The gaskets at the oil filter housing and the oil cooler housing need to be changed.

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