low coolant - cause for concern?

[KevinC]

Yesterday when leaving for work in the morning, my low coolant idiot light came on shortly after starting the car, and stayed on briefly, for about 2 blocks, before going out and staying out. When I started up to head home at the end of the day, same thing. I checked the coolant level and couldn't see it in the bottom of the expansion tank. I topped it up with about 1/3 gallon of distilled water.

Inspection II was done about 8k miles ago and included a flush & fill. I have no signs of anything leaking anywhere. But this seems like a lot of coolant to just "lose". Is it a cause for concern, and if so, what are the possible culprits? I'm at 60k miles and planning on a cooling system sooner than later, hopefully not too much sooner. Thanks for any input from the peanut gallery.

[BCS_ZHP]

Had this happen to my wife's ZHP too. A tech suggested replacing the expansion tank cap ($10), said the rubber seal in there can start to go bad even though it looks okay. He said some coolant can vaporize at higher temps and get past a bad rubber seal. That $10 cap fixed it for my wife's car, subsequently replaced the cap on my car too as PM.

[KevinC]

Great tip and super easy to give it a shot.. one expansion tank cap on its way from Amazon. Thanks!

[johnrando]

Maybe the G.A.S. one?

[KevinC]

Maybe the G.A.S. one?

Too late, I already have OEM on the way. Oh well.

[kayger12]

Based on mileage my first guess is the water pump is starting to go.

Second guess is the thermostat housing.

60k is the failure zone for both.

If you can eyeball the weep hole on the water pump you might be able to see signs of coolant loss. Same for the t stat housing.

Hopefully it's just the cap.

Sent from my kick-A Galaxy S3

[BimmerWill]

Based on mileage my first guess is the water pump is starting to go.

Second guess is the thermostat housing.

60k is the failure zone for both.

If you can eyeball the weep hole on the water pump you might be able to see signs of coolant loss. Same for the t stat housing.

Hopefully it's just the cap.

Sent from my kick-A Galaxy S3

+1 on the water pump. Also with the car running visually inspect the pulley from the top to see if its moving at all in and out that's another tell that the pumps bearings are shot and your gonna have some problems out of it soon.

Sent from my DROID BIONIC using Tapatalk 2

[NorCalZman]

Maybe the G.A.S. one?

Do you use the GAS coolant cap? It says on its website that it is set to much lower pressure than the stock cap (1.2 vs 2 bar). I do not know much about cooling systems, but I wonder how much of a benefit running it at lower pressure would do. Are there any downsides? Easier to overheat? etc.

http://germanautosolutions.com/bmw_solutions/cooling_system/12_bar_coolant_cap/product_bmw_12_bar_cap.php

[johnrando]

No idea, it's a fairly new product. A couple of family members bought them.

[aurelius]

As explained in the product description, their cap set to relieve system pressure at a much lower level than the factory-spec of 2.0 bar, while still maintaining plenty of pressurization for the system to perform properly.

The idea being that the cap is made to relieve pressure when necessary but when set to do so at higher pressure, it doesn't blow its stack nearly as early, thus your unintended pressure relief point can become the plastic tank, thermo housing, or a hose. Or even the little plastic bleeder screw, especially if the threads are jacked up.

The water pump drive belt broke in my '87 E30 last year and of course the coolant got real hot, real quick. But the 1.0 bar ET cap did what it was designed to do and relieved system pressure in the form of steamy water/coolant blowing on to the exhaust header. It's dramatic for a few seconds with all the steam coming from under the hood but at least you know to turn off the motor and coolant loss is minimal.

Whereas with most E46 failures, high pressure is relieved in the form of a cracked expansion tank and if the driver isn't watching the lights or temp gauge, major engine damage occurs due to heat build up from rapid coolant loss.

[LivesNearCostco]

Just checked my coolant and it was low, though not low enough to trip the warning light. Maybe half cup (4 oz) low and probably 5,000 miles since I last checked it. Hoses, thermostat, ET and ET cap replaced 18 months and 19,000 miles ago. Hopefully just minor vapor escaping somewhere and not a HG leak (oil test results pending). Water pump estimated to have 4 years and at least 80,000 miles on it but it's supposedly an EMP Stewart.

Valentine's Day Edit: Checked ET inside with flashlight, no sign of oil in coolant. However some wetness on plastic undertray, beneath ET. Might be coolant leaking from cap gasket, water pump, or one of hoses attached to ET (I replaced 2 of them but there are 3 or 4 total). Leaking coolant outside is annoying but less expensive than coolant leakage inside the engine!

[ryankokesh]

Whereas with most E46 failures, high pressure is relieved in the form of a cracked expansion tank and if the driver isn't watching the lights or temp gauge, major engine damage occurs due to heat build up from rapid coolant loss.

I would know nothing about this... :shifty

[NorCalZman]

so then I assume many of us will be ordering this part :-)

[johnrando]

I will be, just hoping to get more feedback from real life usage from the brave early adopters. :shifty

[Pip]

So far so good on the new cap. Looks great too! Can't comment on the ability to save my car yet, but if I have a cooling system issue I'll be sure to report how the cap works.

I think the comment above really covers what it is supposed to do.

[Junior2552]

Coolant level sensor maybe?
Can't we start with the easy things. Haha. My coolant level sensor went bad once. Then it actually leaked. Oops.

[aurelius]

The OP's symptoms appear to be in line with a functioning level sensor. But those do indeed fail and should be replaced when replacing the expansion tank. A member here lost his motor due, as I recall, to an improperly installed ET. The level sensor was not functioning or was not plugged in and the motor severely overheated while driving home from a long distance ZHP purchase.

[Pip]

Oh also look at the left hand side of the engine bay for a leak on the temp sensor. You'd most likely see coolant on the ground if you were leaking but maybe not if it were pooling in the catch pan. I had a leak on my o-ring (70k miles) which cost <$1 to repair.

[Tnhl1989]

I just replaced my coolant yesterday and it was brown and yellow. It seemed as if there was oil in it as well. What do you guys think of this case before I replaced everything?

[Pip]

I just replaced my coolant yesterday and it was brown and yellow. It seemed as if there was oil in it as well. What do you guys think of this case before I replaced everything?

Do you know if the previous owner or you put yellow/green coolant in the system? I did in mine in a pinch and it was yellow brown when I did a flush with OEM fluid a week later.

Isn't is possible to gain some information about oil in the cooling system by looking at the spark plugs? Or am I thinking of something else?

[aurelius]

Oh also look at the left hand side of the engine bay for a leak on the temp sensor. You'd most likely see coolant on the ground if you were leaking but maybe not if it were pooling in the catch pan. I had a leak on my o-ring (70k miles) which cost <$1 to repair.

Right side of engine bay and will look like this (see pic). Where did you get the o-ring and do you have any size info?

http://i1125.photobucket.com/albums/l584/aurelius3/Random%20BMW%20Pics/tempsensorleak.jpg

[Pip]

Yea I guess I should have specified which way I was facing when mentioning direction. Here is what was provided by Dane. I used this and it worked perfectly - bought at Home Depot.

I think I have one at home I can mail if needed.

7250