I drive a BMW Z4 2003 with 93k miles and I noticed for the first time the other day the coolant fill up light go on when I was driving. I checked the coolant level and it was bone dry. so I filled it up to the very top, and the next morning the light came on again. I pulled over and it was empty again. Not only that, but blue coolant had sprayed all over the inside and outside of my hood and some on my windshield! I let my car cool a little bit, then I filled it up again and drove another fifteen miles. There are no signs that my engine is overheating, as the thermometer arrow has never reached higher than the middle point. Also, I don't smell that "sweet coolant smell" in my car at all, and there's no coolant leaking from the bottom of my car.

I did some research and I'm really hoping the problem is just a loose/old radiator cap, so I ordered a new one online. Anyone know what could be going on?

2 Answers 2


Several possibilities but the one that comes to mind first, due to your spraying issue, is a coolant hose burst or a connection loose.

Either way you want to deal with this promptly as you may cause severe damage to your expensive engine very quickly should the cooling flow to the vital parts get interrupted.

Next up would be a problem with the water pump or the radiator.

When coolant spraying out be VERY careful so you don't get burned by spraying coolant!


I'll first say that it is not a question of your engine not overheating at all, but rather your engine not overheating yet. Empty coolant will absolutely cause your engine to overheat given the opportunity.

You should not drive this vehicle more than is absolutely necessary because running an engine dry can cause a whole host of very expensive issues. Also, you're not going to get an accurate temp reading when there is no coolant running through the engine. The temp gauge is also damped, which mean it will read normal throughout a variety of operating temperatures, and only in severe overheating will it start to move.

Engine coolant splashed in the engine bay is a sure sign of a bad hose, connection, or gasket. On BMW's and especially on this year radiator hoses are a known weak spot. That said, to rule out any engine head gasket failure check the oil dipstick. It should have dark brown/black oil on the end, with no milkiness or opaque appearance.

To trace down the source of a busted coolant line, check the splatter pattern of the coolant, trying to ascertain where the coolant is originating from. There will likely be an area that has much more splatter or looks completely soaked. The area in the engine bay underneath will be the location of your problem.

In terms of known failures, the radiator cap is not usually the prime suspect, as I mentioned above. If you're able, you should replace the upper and lower radiator hoses as a starting point as well.

As mentioned by others, be very careful opening the hood after driving as burning hot coolant can spray on you.

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