Low coolant

[2one3E90]

Every now and then after a 120 mile drive my coolant gets a bit low. As in the bobber in the resivoir goes low but I still see coolant in res. I have been topping up with distilled water for the pass 1200 miles. Is this okay? Will it hurt anything? I live in Socal so it gets hot here anyways. And lowest temps at night have been 51.

[Piper1]

Did you ever check the expansion tank out? It’s not normal to go through that much coolant no. You’ve got a leak somewhere if the tank has never been replaced that’d be my first go to to pull and replace as piece of mind anyway, wouldn’t hurt to do complete coolant system refresh. If you’ve got a pin hole leak in there you may not see the drip. Is there any residue on the plastic cover underneath? Bhg aren’t unheard of now on the m54 but only if it’s really been abused otherwise not common but how's your oil look?

[2one3E90]

Originally Posted by Piper1

Did you ever check the expansion tank out? It’s not normal to go through that much coolant no. You’ve got a leak somewhere if the tank has never been replaced that’d be my first go to to pull and replace as piece of mind anyway, wouldn’t hurt to do complete coolant system refresh. If you’ve got a pin hole leak in there you may not see the drip. Is there any residue on the plastic cover underneath? Bhg aren’t unheard of now on the m54 but only if it’s really been abused otherwise not common but how's your oil look?

Oil looks great. Just changed it with 5W40. Its a 2.5i m54. There is a small leak under my radiator

[Piper1]

Originally Posted by 2one3E90

Oil looks great. Just changed it with 5W40. Its a 2.5i m54. There is a small leak under my radiator

In the expansion tank just below the neck you’ll see a small hole on the inside left where fluid constantly flows. If you remove the cap before starting the car when cold and take a looks inside the tank as the cars running you’ll see a constant flow of coolant. That’s why it will always look like coolant is in the tank unless you’re bleeding out from the bottom of the tank then it’d look completely dry. Going back to the other thread where I linked the pick of my tank with the hair line crack on the side it’d drain to the bottom of the crack so there’d still be little at the bottom. If your leak is somewhere other than the tank with the coolant flowing how it does when you top off the tank and next run it’ll take up the space where there might be a gap.
The danger is you could be introducing air into the system if you’re not bleeding it out every time you’re topping off. The m54 is easier to bleed, just raise front end ie ramps and idle at 1500rpm till you don’t see any air and it’s a fluid stream coming from that small left hole inside the tank I mentioned. But over all it sounds like you need to do a coolant system refresh. Hoses can take a toll if you’re getting air into the system. I didn’t bleed out good enough on my 87 Supra and blew the old hoses after a radiator replace once. Not fun lol. Do it right. If you know the rad is leaking replace that, hoses and the tank at the same time.

Edit: just to add crank inside thermostat hot and on high when doing it. I know there’s how tos here and on the z4-forum for the m54 bleeding procedure but very easy and straight forward.

[2one3E90]

Originally Posted by Piper1

In the expansion tank just below the neck you’ll see a small hole on the inside left where fluid constantly flows. If you remove the cap before starting the car when cold and take a looks inside the tank as the cars running you’ll see a constant flow of coolant. That’s why it will always look like coolant is in the tank unless you’re bleeding out from the bottom of the tank then it’d look completely dry. Going back to the other thread where I linked the pick of my tank with the hair line crack on the side it’d drain to the bottom of the crack so there’d still be little at the bottom. If your leak is somewhere other than the tank with the coolant flowing how it does when you top off the tank and next run it’ll take up the space where there might be a gap.
The danger is you could be introducing air into the system if you’re not bleeding it out every time you’re topping off. The m54 is easier to bleed, just raise front end ie ramps and idle at 1500rpm till you don’t see any air and it’s a fluid stream coming from that small left hole inside the tank I mentioned. But over all it sounds like you need to do a coolant system refresh. Hoses can take a toll if you’re getting air into the system. I didn’t bleed out good enough on my 87 Supra and blew the old hoses after a radiator replace once. Not fun lol. Do it right. If you know the rad is leaking replace that, hoses and the tank at the same time.

Thank you so much. Wow okay ill try bleeding it. I have rhino ramps. Youtube perhaps has the bleed procedure. Sometimes even if i dont drive it for 1 week the coolant is still plentiful and the bobber is up when I open the cap.

[pungo]

Just so you know, there's a lot more properties to anti-freeze than the freeze prevention part
Always top off with 50/50 mix of BMW coolant and distilled water, no matter how warm of a climate you live in.

[MarinerZ4C]

. . . .getting the front end up on ramps is still great advice for the z4's with N52 engines (LCI, aka Facelift). Those cars have electric water pumps and auto-bleed, but on my car, two auto-bleed's left trapped air until I put the nose up.