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Discussion Starter · #1 ·
330ci 2003

Hi all,
Couple weeks ago I noticed the low coolant light. I bled the system and topped it up.. probably half a litre.
Today I had the same light, expansion tank is almost empty.. havent topped it yet.

There is pressure on the rad hoses.. I checked the oil cap and its not... pretty.
Bear in mind I do some short 1.5mile trips to work quite often.. I have heard this could be a culprit. But coupled with the drop in coolant I am suspicious.

Anyone have any insight?
Thanks all
918487
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Yeah...I make short trips to work...I usually hop on the expressway shoot to the next exit . One week I took the slow scenic route each day. My cap looked like yours. Now I continue to hop the expressway (heat up the engine real good) condensation appears no more under the cap.
Concerning the coolant...it takes me a couple of top offs to get the fluid level ( especially after burping the system) just where it will not trip the light when I'm having a little fun on a straightaway...no leaks tho.

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Discussion Starter · #4 ·
Yeah...I make short trips to work...I usually hop on the expressway shoot to the next exit . One week I took the slow scenic route each day. My cap looked like yours. Now I continue to hop the expressway (heat up the engine real good) condensation appears no more under the cap.
Concerning the coolant...it takes me a couple of top offs to get the fluid level ( especially after burping the system) just where it will not trip the light when I'm having a little fun on a straightaway...no leaks tho.

Sent from my SM-J727T using Tapatalk
Thanks for the info getty!
Ill clean it off, see how long it takes to build up. Needed an excuse to be less lazy and walk in anyway.. haha

Ill top off the coolant and keep and eye on it. The needle has never gone over mid so I’m pretty confident in it. Replaced a few items a while back too.. expansion tank, water pump etc.

Cheers 👍🏼
 

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2016 340i xD 6-spd
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You probably are leaking coolant, unless you hadn't bled it or used the heat since you worked on it last.

Some leaks are hidden pretty well...so look pretty well. You topped it up a couple weeks ago and it's low again...if it gets low a third time, you'll know for sure, I guess...but you should be pretty sure right now. :)
 

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E30M3 Race F10 535 R1150Rt M Coupe
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Hard to say, could be coolant, could just be normal 'mayo" from short tripping the car.
Are you 101% sure there are NO external coolant leaks, hot or cold?
 

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Cap isn’t bad looking, but you need to find the cause of coolant leaking.
+ 1 on this....Your cap looks normal for this time of year, and short trips

If you're coolant leak is not obvious, I suggest you buy the UV dye kit and put 1/2 of the small 1 oz (30ml) bottle of dye in your expansion tank...Run the car for at least a day (and not just 2 short round trips) and then use the UV glasses and UV flashlight at night to snuff out your leak.

Here is an example...you will need to buy the UV Dye separately:

REALHUNLEE Auto Air Conditioner Leak Detector Tool Flashlight Oil AC Dye Leak Test Detection Kit Pro 68 LED Flashlight with UV Protective Glasses
by Realhunlee Direct
Learn more: https://www.amazon.com/dp/B08DVBM9ZF/ref=cm_sw_em_r_mt_dp_Hs18FbFMCW1E2
 

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Discussion Starter · #8 ·
+ 1 on this....Your cap looks normal for this time of year, and short trips

If you're coolant leak is not obvious, I suggest you buy the UV dye kit and put 1/2 of the small 1 oz (30ml) bottle of dye in your expansion tank...Run the car for at least a day (and not just 2 short round trips) and then use the UV glasses and UV flashlight at night to snuff out your leak.

Here is an example...you will need to buy the UV Dye separately:

REALHUNLEE Auto Air Conditioner Leak Detector Tool Flashlight Oil AC Dye Leak Test Detection Kit Pro 68 LED Flashlight with UV Protective Glasses
by Realhunlee Direct
Learn more: https://www.amazon.com/dp/B08DVBM9ZF/ref=cm_sw_em_r_mt_dp_Hs18FbFMCW1E2
Thats a good idea, havent heard of this before..
I will top it up, run it again and see if it drops again.. if it drops for a third time I think theres definitely a leak.
If so ill take a look into this stuff..

Appreciate your help
 

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I would try to pressurize the system using a kit similar to the following:


I have the system listed above and it has helped me find leaks that weren't obvious. You may be able to borrow a kit from an automotive store. Call and check. I wish you luck.
 

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Have you checked to see if the lower radiator hose coolant temperature sensor is leaking coolant?
I've had to replace mine a couple of times.
 

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2011 335i xDrive, 2003 325xi 5spd SOLD
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Pull the intake and try to check the sides of the radiator. I had a hairline crack in mine. That amount of moisture on the cap is nothing much, just take it on a nice spirited drive to clean it out.

You should only be scared when you see it in the coolant is my rule.
 

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Half a litre is going to show up if its leaking. Use a flashlight, or get under car, pull belly pan.
 

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Could just need a top off from using the heater. These engines can loose a few oz in 2,500 miles or a few months depending how many miles and how often you use the heater. I notice that a lot with bmws from working on them with my dads friend every summer when a client of his complains about the coolant light when they come to his shop. I'd pressure test it and see if you have any leaks. First place I check is the cap on the expansion tank where you check your level. See if the bottom O ring is flat or coming off the threads. Could be the cause of the loss. If that looks fine, then I'd do a pressure test to see if any of the components on the system is bad from normal use and being 5-10 years old. Hope this helps you. And also take off the bottom shield, it'll be a lot easier to see where its leaking when you have it jacked up or on a lift. -Jordan
 

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E30M3 Race F10 535 R1150Rt M Coupe
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Thats a good idea, havent heard of this before..
I will top it up, run it again and see if it drops again.. if it drops for a third time I think theres definitely a leak.
If so ill take a look into this stuff..

Appreciate your help
Keep in mind, as an example but not out of the question, if the coolant expansion tank cap was bad, that would be a leak also.
Keep an open mind/eyes before you do anything rash.
 

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Could just need a top off from using the heater. These engines can loose a few oz in 2,500 miles or a few months depending how many miles and how often you use the heater.
I don’t get this. Once it’s bled properly, using the heater one or thousands times doesn’t consume more coolant than not using.
 

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Discussion Starter · #16 ·
UPDATE :
So I topped up the coolant today and made double sure to not spill a single drop. Last time I saw some droplets around the bottom of the expansion but I had spilled some so put it down to that.
Today I didnt spill a drop and still it was dripping.
Seems to be the connection between expansion tank and radiator.
After unclipping and reclipping the tab for the connection the droplets seemed to stop but I will keep an eye on this.

The expansion tank was replaced only a couple of months ago.. so thats good.
I also did the mechanical fan delete not long ago so its very likely I knocked that tab..

Here is a photo of the problem area.. fan removed to get a good image.

Thanks for all you guys advice!
Wish I knew about this forum when I had my last E46... haha
918625
 

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UPDATE :
Seems to be the connection between expansion tank and radiator.
After unclipping and reclipping the tab for the connection the droplets seemed to stop but I will keep an eye on this.
It's not the radiator bracket and not the radiator. Without supporting the bracket from below (using scissor jack and piece of wood) it will sag when pushing down on the ET, causing a cocked connection and potential leak. It's better to lube the connector O-ring and the male mating surface with silicone grease (brake grease) to avoid damaged O-ring.
 

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I don’t get this. Once it’s bled properly, using the heater one or thousands times doesn’t consume more coolant than not using.
Sometimes cars especially my 325i occasionally need a few oz in 6-8 months due to the water in the cooling system evaporating from normal operation. Like around June when it gets warmer in the year. But you never know. Just saying from personal experience. My friends E46 M3 had the coolant light come on after 2,700 miles when he did his cooling system. He pressure tested the system and did a leak down test to find issues, couldn't find anything wrong with his M3. My dads friend had it on a lift at his shop to see if its leaking. Couldn't find anything wrong with the system or the head. So he bled it and fixed the issue. Only thing he could think of is maybe it evaporated some distilled water from normal operation. Just saying from what I've experienced and heard with these cars.
 
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