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BMW 3-Series (E90 E92) Forum > BMW E90/E92/E93 3-series General Forums > General E90 Sedan / E91 Wagon / E92 Coupe / E93 Cabrio > Help needed please coolant loss issue



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      01-07-2021, 03:50 PM   #1
bizzleb109
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Help needed please coolant loss issue

Hi everyone this has been baffling me for a while now. I have a 2007 335i auto everyday I have to top up my coolant I drive about 30 miles all in all next morning coolant level really low the float literally sits at bottom I don't get any low coolant warning lights either.
I had my water pump and thermostat changed about 7 months ago and just recently had my radiator replaced but still losing coolant. Don't have any white mayo mix in coolant tank engine oil cover lid. Had a indy inspect car and was told no leak could be detected. Any thoughts please?

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      01-07-2021, 05:26 PM   #2
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By inspect do you mean he took a glance and sent you on your way? Sounds like it. Get a pressure tester and pressurize the cooling system in it and you should see a leak, also could try putting dye in it to see where it's coming out of more easily. Points I would look at would be the plastic coolant outlet in front of the cylinder head, upper radiator elbow, coolant overflow tank spaghetti hose that goes over the radiator and the seam where the radiator plastic and metal crimp together.
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      01-09-2021, 01:12 PM   #3
bizzleb109
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No they had car about 3 days said they could not find leak but I also think they do not have equipment to do a pressure test. Today early in morning I topped up the coolant drove the car about 2 miles over a period of 10 mins got home wanted to check coolant so started opening lid and coolant started pouring out is this normal?
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      01-09-2021, 01:18 PM   #4
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Quote:
Originally Posted by bizzleb109 View Post
No they had car about 3 days said they could not find leak but I also think they do not have equipment to do a pressure test. Today early in morning I topped up the coolant drove the car about 2 miles over a period of 10 mins got home wanted to check coolant so started opening lid and coolant started pouring out is this normal?
Yes, the coolant has expanded due to heat and will pour out like that when you undo the cap while it's hot.

If you have a low coolant light but your coolant isn't low, you may have a bad sensor. First, try knocking the tank a bit when it's cool. This can dislodge a stuck float. Next, try replacing the sensor. Very easy to do and doesn't require removing anything to get to it. If it still tells you it has low coolant, you'll have to replace the tank (as was my case). This is also true of the opposite case: a malfunctioning sensor that doesn't report low coolant is equally an issue.

You'll likely slowly lose coolant over time. Very slowly. This is normal. If you look at the expansion tank with the cap off you'll see a small weep hole for both pressure and coolant. The expansion tank cap has two O-rings for this reason: when the valve opens, pressure is released through the space between them.

When the expansion tank vents to prevent too much pressure, it is entirely possible for some coolant to come with it. The coolant that comes with it drains out and to the ground, in addition to the excess pressure. It's very little and should only require some minor topping off over a long period of time.

I don't think I've had a BMW where I didn't need to top off a little coolant every once in a while. If you need to fill it from minimum every month, then you've got a more significant leak that should be identified using a pressure tester.

Last edited by Welcome to NBA Jam; 01-09-2021 at 01:25 PM..
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      01-09-2021, 03:16 PM   #5
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Quote:
Originally Posted by bizzleb109 View Post
No they had car about 3 days said they could not find leak but I also think they do not have equipment to do a pressure test.
fwiw, Autozone has a loaner pressure testing kit.

You can go the route of doing the dye test (they sell the dye too), but my guess is that once you pressurize the system you'll figure out where your leak is...particularly since yours seems to be leaking quite well.

(edit...I just noticed that you're in "essex". I'm not guessing that's the UK? So I don't know if you have something equivalent to Autozone, that loans out tools. Sorry.)
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      01-10-2021, 02:44 PM   #6
bizzleb109
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Yeah in the UK......today I noticed a puddle of water so hopefully tomorrow will inspect further to see if I can locate it.
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      06-22-2021, 04:30 PM   #7
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I recently had a similar issue, replaced hoses and the radiator as Pump and Thermostat were replaced a few months back. Then spent a week messing about trying to source the leak. Turns out it was the Heater Exchange return line that feeds into the bottom of the radiator. Only leaked when it was hot. Changed the o-ring and it fixed the issue.

Hope this helps.
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      08-09-2021, 07:34 AM   #8
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With the coolant leak from the heater matrix you described, how did you find that this was the case? I'll check as I have a pressure test kit and look in this area. what sort of job was it to do?
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