Coolant level

[jamesembry]

My car can sit for days and the level in the expansion tank shows a little low, then if I loosen the cap to fill it up, it goes to the cold level once the pressure is released. Is that normal? Does the system need to be bleed again? I recently did a complete cooling refresh so that is very possible.

[BMWManiac]

Doesn't sound like something I would worry about....but it never hurts. I would drive around with the heat on full black/90 degrees, car fully warmed up and that should help instead of trying the messy approach, but again, sounds like you're fine

[JGard]

yeah, if the level rises up once you open the cap it means there's still air in your system. Keep trying to bleed it out

[jayjaya29]

My car has always done this. Never had any issues in over 20,000 miles, just live with it.

[Dres325is]

My car has always done this. Never had any issues in over 20,000 miles, just live with it.

Same here. But there was a thread last week that I cant seem to find and someone said that this was a sign of possible head gasket leak. Had me freaking out for a second but my car still runs find and no coolant loss so I got over it

[kevinwilly]

Fill it while it is cold and the car is running with the heater on and the bleed screw open. Once you get it right it won't move on you when you pull the cap off anymore. You should have no bubbles coming from the bleed screw and coolant should be right to the top of it. At that point you should also be at the cold fill line in the reservoir. Put in bleed screw, put on cap, call it a day.

[crqflier]

Sounds like a possible hg leak. I've been around and around the block on this - no pun intended. The reality is the cooling system is a closed system. If the system is remaining pressurized overnight or over days, that extra gas is being introduced somehow. Re-bleed and monitor. If it keeps happening, you need to decide how much you care and what diagnostics to run, recognize that none are truly confirmatory (you can have a decent leak down test yet still need a new hg, etc). Hopefully it's not the hg but be watchful.

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[M3C]

This might be an indication that your coolant reservoir needs to be replaced. Most likely the pipe (that is visible when you open the cap) has cracked, this happens after years of use and from high heat.

[jayjaya29]

My motor ran with the mysterious disappearing coolant for 3 years with full performance and no loss of coolant. I tested the coolant for combustion byproducts, got a negative result. I also did a coolant pressurization test which held steady for 12 hours. If it has no palpable effect on the performance of the car, who cares.

[Bronickishere]

My motor ran with the mysterious disappearing coolant for 3 years with full performance and no loss of coolant. I tested the coolant for combustion byproducts, got a negative result. I also did a coolant pressurization test which held steady for 12 hours. If it has no palpable effect on the performance of the car, who cares.

Agreed. Only annoying part in that respect is to having to keep buying jugs.

I have the dreaded rear coolant hose leak that I really have no way to get to. Looks like it's leaking in the center of the car but it runs down the tranny and then on the ground. Planning on doing a 5 speed to 6 speed swap in the near future. Will take care of it then.

[TXBDan]

If you had the cooling system open its likely just air in the system. Check out the "cold bleed" method here:
https://www.bimmerforums.com/forum/s...ead&p=29394803

[JayhawkM3]

I have the same problem and finally saw that I had a VERY slight leak...it leaks only enough to hit the lower side of the gasket and burns off/evaporates before it was noticeable. Time to clear the WHOLE damn coolant system out and get somethgn that will last!

[ewrjontan]

Now I am curious. I have a little bit of a leak, mostly when it is warmer temperatures outside. Every few weeks I have to add a little bit. By opening the expansion tank and adding some coolant, am I introducing air into the system or should the system still be fine?

[jayjaya29]

Now I am curious. I have a little bit of a leak, mostly when it is warmer temperatures outside. Every few weeks I have to add a little bit. By opening the expansion tank and adding some coolant, am I introducing air into the system or should the system still be fine?

Taking the radiator cap off does not introduce air into the system.

[usedunderwear]

Taking the radiator cap off does not introduce air into the system.

What if you replace the coolant level sensor from the bottom of the coolant tank? Does that introduce air into the system?

[jayjaya29]

What if you replace the coolant level sensor from the bottom of the coolant tank? Does that introduce air into the system?

Well you gotta remove the expansion tank to replace that sensor, so yeah.

[usedunderwear]

Well you gotta remove the expansion tank to replace that sensor, so yeah.

Thank you. Found out yesterday after I replaced my coolant level sensor....it has air in the cooling system so I'm going to re-bleed it again

[ben4bama]

The coolant level should only drop not raise when loosening cap. If it goes up you have air in system. I had replaced my entire cooling system 2 years ago and just figured out my new Behr expansion tank was faulty with a crack in the inner tube as I could never bleed all the air out and the level would go higher and higher after every drive. I finally figured it out when I could hear hissing in the tank with cap off after bleeding it and running engine for a few mins after. Replaced with new tank and the level has been at kalt ever since with no hissing. Moral of the story is your expansion tank could be your problem as it was for me.