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Old 04-13-2019, 01:56 PM   #1
Filmy
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Coolant Level

This isn't a Touring-specific question, but for all automatic E46s. I have revamped my cooling system with new pump, hoses, reservoir, and now reservoir cap and I still have a very slight coolant leak up near the top of the res. I have been watching the coolant level (using the red stick, second ball) and topping it off regularly every few days. I have a coolant system pressure tester that I attached to the reservoir and pumped it up - it held pressure with no drop. At that point, the only variable was the cap, so I replaced it.

But the same minor leak still exists. Everything is tight, bleed screw as well. Pulled the top hose assembly off and re-attached it. Same story - residual coolant on top of the res after driving at full temp.

So when topping off coolant in the res, the red level stick can only come up so high (to the second ball), and when it does, that coolant level is deep down in the reservoir - lower than you'd think it should be. It's lower than the upper hoses, it's lower than the bleed screw. In my case, I've always topped off the coolant before it gets lower than the first ball on the red stick.

Knowing all of this, am I over-filling the reservoir and it's just burping back out under pressure because I've over-filled it? Is it normal for the two upper hoses to be above the coolant level in the reservoir?
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Old 04-13-2019, 02:23 PM   #2
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Quote:
Originally Posted by Filmy View Post
This isn't a Touring-specific question, but for all automatic E46s. I have revamped my cooling system with new pump, hoses, reservoir, and now reservoir cap and I still have a very slight coolant leak up near the top of the res. I have been watching the coolant level (using the red stick, second ball) and topping it off regularly every few days. I have a coolant system pressure tester that I attached to the reservoir and pumped it up - it held pressure with no drop. At that point, the only variable was the cap, so I replaced it.

But the same minor leak still exists. Everything is tight, bleed screw as well. Pulled the top hose assembly off and re-attached it. Same story - residual coolant on top of the res after driving at full temp.

So when topping off coolant in the res, the red level stick can only come up so high (to the second ball), and when it does, that coolant level is deep down in the reservoir - lower than you'd think it should be. It's lower than the upper hoses, it's lower than the bleed screw. In my case, I've always topped off the coolant before it gets lower than the first ball on the red stick.

Knowing all of this, am I over-filling the reservoir and it's just burping back out under pressure because I've over-filled it? Is it normal for the two upper hoses to be above the coolant level in the reservoir?
If the second ball is level with the filler neck when cold then it's full. The airspace is to allow room for expansion when hot, as the liquid cannot compress, only the air can.

https://www.newtis.info/tisv2/a/en/e...-check/ANzABPr
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Old 04-14-2019, 06:34 AM   #3
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OP, it can be a pitb to get the upper hose connected to both the radiator and ET, particularly the ET. Look carefully under that connection (the smaller one). Could be you just need to reattach that hose. Remove...add silicone lube (or coolant 'as' lube) and try again...and push the ET forward until you hear a click...and good luck.

If not, when you did the ET, did you replace the cap? They do go bad.
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Old 04-14-2019, 07:09 AM   #4
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Yes, I agree with dmax, I had the same issue back in the day. The smaller hose was not fully engaged even though the clip as fully seated downward. Hold and Push the hose and the tank together to get it to seat.
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Old 04-14-2019, 07:19 AM   #5
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@filmy- have the same issue.I have no pressure tester but what I do see is some residue around the radiator(old) neck just anterior to the large inlet upper hose connection.I suspect mine has a hairline crack .Replacement radiator on hand ready to be put on just waiting for the correct manual drain.The radiator is for an auto.My ET ,Cap, hose water pump, thermostat are new for a refresh.
I may be wrong but hope this solves my small leak.

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Old 04-14-2019, 11:24 AM   #6
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Clean all residual and reduce coolant to top ball .
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Old 04-17-2019, 02:01 AM   #7
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Yes to all, and thanks for the tips. As I said in my post, I have all new parts and have pulled off the upper hose, checked the fittings & O-rings and re-attached it. Reservoir is smashed properly in place. I was just a little surprised that the correct(?) coolant level is lower (in the reservoir) than the upper hose(s), and if filling coolant above those hoses is a waste of coolant.
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Old 04-17-2019, 07:53 AM   #8
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Think of the coolant in the expansion tank as 'extra' coolant - because essentially that is what is is. For the engine to operate at the correct temp only the radiator needs to be full. The function of the expansion tank is exactly what its name says - to provide room for the coolant to expand when it gets hot. If there is any coolant at all in the tank when the engine is cold it is enough. I would try leaving the coolant at the lower mark on the stick and then checking for residue after a few days. As Archbid said overfilling is the danger here. BMW uses a '2 bar' or 28 psi pressure relief cap. That is a lot of pressure on a square plastic tank.

On my cars I keep just enough coolant in them to keep the idiot lite out. If I don't at least keep that much in it my wife bugs me until I add some.
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Old 04-17-2019, 10:41 AM   #9
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Originally Posted by Filmy View Post
I was just a little surprised that the correct(?) coolant level is lower (in the reservoir) than the upper hose
I think you were thinking about the overflow reservoir tank system popular in Japanese and Korean cars, which you fill the radiator until the level is higher than the upper hose, or full to the rim. There is no air in this system in the pressurized coolant components!!!!

In the E46, the system NEEDS a about a liter air volume in the tank at ambient 70F, or something will explode (the cap released pressure and saved your neck this time).

Last edited by Sapote; 04-17-2019 at 10:42 AM.
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Old 04-22-2019, 02:23 PM   #10
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Hello. I'm not a professional mechanic, but I have worked on quite a number of e46 (and e36) coolant systems over the years, and the problem sounds to me like what most of the people in this thread are saying- you're over filling it.
If it checks out with a pressure tester and the cap is new you've pretty well covered it.
If you overfill it, when it's pressurized it will be too full and come out the cap.
Don't just eyeball it or assume the red level indicator stick is off, there's no reason to think it's wrong, fill it until it's just below the 'full' mark (so there's still a little room for the stick to come up more) and see if the problem persists.
Don't keep topping it up either, unless it goes below the 'low' mark, it doesn't need to be full the the top at all times, there's a safe range, as indicated on the red stick.
Hope that helps.
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Old 04-22-2019, 03:48 PM   #11
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If its a hairline crack or small pinhole, try spraying a small amount of soapy water around the area to check for any bubbles. You need to do it when the car is hot so the system is pressurized. Just make sure you rinse the soap off before it cools down so the vacuum created on cool down won't pull any residual soap back in through the crack. You don't need to drown it, just use a dropper to put a small amount where you suspect the leak is.
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Old 04-22-2019, 05:35 PM   #12
Filmy
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Thanks for the tips, guys. I've let the coolant level stay as low as possible in the reservoir, while still floating the red stick up to the second ball. No overflow since, but I'm still keeping my eye on it. Still surprised that it needs that much air in the system.
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Old 04-23-2019, 07:29 AM   #13
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OP, kudos for using a pressure tester. I am in agreement with those suggesting that you are over filling. The ET should be filled to the minimum level or slightly below. Glad to hear the issue is resolved.

Quote:
Originally Posted by shadetreemech View Post
Think of the coolant in the expansion tank as 'extra' coolant - because essentially that is what is is. For the engine to operate at the correct temp only the radiator needs to be full. The function of the expansion tank is exactly what its name says - to provide room for the coolant to expand when it gets hot. If there is any coolant at all in the tank when the engine is cold it is enough. I would try leaving the coolant at the lower mark on the stick and then checking for residue after a few days. As Archbid said overfilling is the danger here. BMW uses a '2 bar' or 28 psi pressure relief cap. That is a lot of pressure on a square plastic tank.
Good info here and nicely explained.
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