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General E46 Forum
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Old 01-31-2012, 03:48 AM   #1
Bert82
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Coolant Light coming on & off

Hi folks, my coolant light keeps coming on then off. The little floating device is at the correct level in the expansion tank indicating the coolant is full. Would it be a faulty sensor or air in tank thats making this happen?

Thanks
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Old 01-31-2012, 03:57 AM   #2
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I would bleed the system and fill it with OEM coolant and distilled water, and also check for any cracks on ET, cap, hoses, even for minute ones. Check the engine temperature with the cluster test or with any tools. May be the sensor is faulty but doesn't hurt to check everything if you don't know the history of the car.

When was the last time the coolant system was checked/changed?
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Old 01-31-2012, 05:10 AM   #3
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Doesn't hurt to bleed the system as stated. Is the level consistent when the car is COLD before you first turn it on in the day?
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Old 01-31-2012, 05:32 AM   #4
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Thanks both. I'm not sure when the coolant was last changed, I've only had the car for 2 weeks. The temperature is always fine and never go's into the red. I have checked the fluid level when cold and it's consistant. I'll get it checked over.

Cheers
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Old 01-31-2012, 05:37 AM   #5
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When was the last time you had cooling system work done? How many bleeding threads did you read? And, have you looked for leaks with xl50?

Compare level in a.m. on level ground...the same level ground so you're measuring change reliably.
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Old 01-31-2012, 06:33 AM   #6
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I also have this same problem.. seems I have a lot of the problems popping up lately... ET float is perfect, but coolant light comes on while cruising, but goes off while idling, temp gauge never moves, sound like your problem OP? I have yet to tackle it, but I plan on doing a cooling system overhaul this spring.
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Old 01-31-2012, 08:17 AM   #7
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fwiw, everytime my coolant light has come on, there has been some kind of leak somewhere. it is possible the sensor could be bad, but each of the 4 times mine has come on, it was a slow leak.
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Old 01-31-2012, 08:20 AM   #8
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If you only had the vehicle for 2 weeks... You may want to see if you can have the previous service record pulled. This will give you some insight on what other problems you will need to take care of, Before it becomes a costly repair. Also, you need to research and learn more about your E46, here
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Old 01-31-2012, 10:30 AM   #9
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My coolant light came on for a short period of time, so I checked the coolant level. It looked fine and I went about my business. A week later I came out to a pool of coolant and a ruptured ET and upper radiator hose. I would take a more thorough look or have someone inspect the system. Welcome to the achilles heel of the E46.
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Old 01-31-2012, 10:49 AM   #10
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@Bert82
Since you just purchased the vehicle (from dealer or individual?) If there is a warranty you should have them cover any costs for repair. Make sure there's been No use of stop-leak/rad. sealants used. It will ruin your cooling system.

The coolant warning light doesn't come on & off without cause... usually there is a leak developing. Some people can't comprehend how a leak can come and go > Search my YT vids on explanation/diagnosis.

Main thing is to definitely not ignore the issue, thinking you can "just live with it" and fill up the exp.tank every few weeks/months... You're gambling with your motor possibly overheating. Just a heads up.

Last edited by BimmersGarage; 01-31-2012 at 10:55 AM.
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Old 01-31-2012, 11:03 AM   #11
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You may have low coolant. Note that the coolant will expand and contract quite a bit do to temperature. I have seen this problem often on E46 where the coolant light does not come on until the outside temps dip close to or slightly below freezing, but then do not come on if the temps stay above freezing.

The first thing you need to do is understand these cars have an expansion tank and there is a float level indicator inside this expansion tank. You need to check your coolant when cold and make sure you use the float properly and do not overfill the expansion tank with coolant or you WILL be replacing the expansion tank in the new few days! Many times you need to pick the float up and drop it back down to make sure the float is not stuck so you can properly gauge the coolant level.

Also while you are under the hood, check for this very common slow leak a the fan switch in the lower radiator hose.

Look straight down on the passenger side of the radiators at the lower radiator hose. You will see something in the lower radiator hose with a small wiring connector, this is the fan switch.

There is an O-ring on the neck of the fan switch that shrinks and causes a slow leak. If the fan switch is wet at all and/or there is a wet mark below the lower radiator hose on the under cover, then your fan switch O-ring is leaking. This is a very common problem.

O-ring is no listed in the parts catalog, it is BMW Part #13621743299, about $2 and it does not require any tools to do the job, just your fingers to unlatch the connector and release the fan switch with the 2 plastic tabs. Perform on a cold car, you will loose only a slight bit of coolant due to cooling system vacuum.

Use on BMW coolant and distilled water to refill/top off the system.
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Old 01-31-2012, 02:25 PM   #12
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Thank u all, thats great
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Old 01-31-2012, 02:35 PM   #13
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Hi again, just to be sure, when cold, is the flotation stick in the ET supposed to be level with the top of the filler cap or is it supposed to stick out as per the small diagram next to the ET?
Thanks
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Old 01-31-2012, 03:33 PM   #14
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Make it so the balls straddle the top of the filler neck. You don't want to overfill it. You should be between min and max, so as not to risk being over full.
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Old 01-31-2012, 03:36 PM   #15
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^+1 What dmax said.

Keep in mind the colder is gets, the more the coolant contracts so the level will drop. I would say at temps between 40-80F you want it about 1/2, so when it gets really cold the level does not drop below the threshold to trigger the light.
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Old 03-11-2012, 04:39 PM   #16
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Is this the fan switch that develops a common leak?

http://flic.kr/p/bpkTgA
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Old 03-11-2012, 04:54 PM   #17
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That's it. The IAT 0-ring jfoj has in his sig fits right on it. Just remove connection, squeeze tabs, and wiggle the sensor up...replace o-ring and put it back. No coolant will leak at all.

But, there are other sites around that leak...this is a common one, though, as you say.
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Old 12-30-2013, 09:56 AM   #18
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Ok, so i had a new radiator, expansion tank and thermostat fitted in my e46 sedan. Unfortunately, the expansion tank's coolant sensor (the one in the bottom) was old and had to be replaced too with the other items. I have been getting the coolant indication light ever since. Lights up with the start of the engine and goes off when the thermostat kicks in. Every day the same thing. Coolant level is at just fine. Checking it every time when engine is cold.
Any ideas?

PS. I haven't seen any leaks yet..

Last edited by diosak; 12-30-2013 at 09:57 AM.
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Old 07-17-2014, 12:24 PM   #19
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Originally Posted by diosak View Post
Ok, so i had a new radiator, expansion tank and thermostat fitted in my e46 sedan. Unfortunately, the expansion tank's coolant sensor (the one in the bottom) was old and had to be replaced too with the other items. I have been getting the coolant indication light ever since. Lights up with the start of the engine and goes off when the thermostat kicks in. Every day the same thing. Coolant level is at just fine. Checking it every time when engine is cold.
Any ideas?

PS. I haven't seen any leaks yet..
So, what was the issue? My coolant light is acting mysterious as well.
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Old 08-03-2014, 11:51 PM   #20
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Ever since I overheated my car, my coolant light has randomly been comic on while driving. Car runs good, system doesn't require any coolant, I'm just wondering if the sensor was damaged.
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