Where's My Coolant Going

[MARKSS]

My OBC gave me a low coolant warning a couple of weeks ago. The coolant was a little low. I checked for leaks, found none, and added coolant. This morning I got the warning again. This time the level was much lower. I still found no leaks. I topped it off again. WTF.... I changed the thermostat about 2 months ago and haven't had any issues until now, even under hard driving. Any ideas?

[TH3 Shifty]

do you see an light smoke on start up? does the exhaust smell like coolant? if so.. you have a blown head gasket..

also look for traces of coolant being burnt off on the exhaust manifold.. or down the side of the engine.. this somtimes happens and you wont see anything on the floor ..

[MARKSS]

I haven't noticed any smoke. I did smell coolant the other day when I got home from work. Is there usually something that causes a head gasket to blow. If it is blown is this a major problem, or is it an easy fix?

[CMG]

Check your oil to make sure coolant isn't mixing. That's a sure sign of a blown headgasket.

[MARKSS]

I actually just changed the oil today and didn't notice any sign of coolant.... of course I didn't take a real close look. Would it have been obvious?

[Alex@VMwerks]

it is very common for the coolant sensor (beneath the expansion tank) to go bad. If you aren't losing coolant, it is probably that.

[MARKSS]

Would my car be running different if the headgasket was blown. I haven't noticed any drop in performance or anything suspicious. Temp. is always where it needs to be and everything runs smooth. I think the sensor is fine, because when I add the coolant the warning goes away. I'm wondering since I have just recently been using the heater in the mornings if it is diplacing air that may have still been trapped in the system. Is this a possibility?

[thejlevie]

A leaking water pump is a common cause that is easily overlooked. A leaking seal may only loose coolant when the engine is running and it may not be visible from the top (and isn't all that easy to see from the bottom). A pressure test of the cooling system will usually find leaks other than those involving the head gasket. And since you've smelled coolant and haven't had any overheating my guess is a leak rather than a head gasket problem.

[dcroghan]

you mentioned that you smelled coolant so you are def losing it somewhere.

I would check the thermostat that you just replaced and around the waterpump like mentioned before.

You could also try a compression test.

[TH3 Shifty]

yes to the above poster... it could be leaking down the side or front of the block and burning off if you dont see any were you park..

coolant in the oil will result in a "chocolate milk" type look to the oil itself.

do this as well... start the car.. let idle.. give it a few quick revs, quickly walk to the back of the car and smell the exhaust.. if you smell a slight coolant smell.. you're burning coolant and you have a blown head gasket...

a blown head gasket can be small or major.. the small kind wont hinder performance all that much..

but since you recently messed with the coolant system, i would retrace your steps and make sure everything is tight and all bolts torqued to spec. Also make sure you retightend the bleeder valve ...

[Balthazarr]

Does the heater work as it should?
Check for coolant around the heater valve and hoses under the manifold as well as the
rear hose connection to the head.

As has been stated, coolant will evaporate very quickly, if it's running down the block or head.
Should be able to see a trail of whitish residue.

[sivikvtec]

bump for the resolution to this. I'm having the same symptoms and would like to know how this all worked out for you.

[99E36M]

Not sure if this makes you feel any better but the three E36s my family has (mom's 323ic, gf's 328ic, and my M3) all like to drink coolant. It has stumped me for a year now. I recently redid my gf's cooling system and every month or so she gets the low coolant warning. At first I figured it was just sir bubbles slowly coming out but I'm not so sure anymore.

[will v]

I have the same problem right now.

Every so often I get a low coolant warning, fill it up. I put the car up on jack-stands a couple of weeks ago and noticed that I am getting coolant running down the lower rad hose(passenger side) that then drips onto the ac lines and then blows back over the suspension when driving the car.

With all of the accessories and shrouds on the front of the motor I cannot determine the source but it is likely a hose failure at the thermostat housing or the water pump gaskets.

I have a high flow water pump going in and the metal thermostat housing this weekend so when I have the car apart I will be able to see where it was coming from.

My first thought was a slight head gasket leak but I had none of the symptoms as it seems is the same case as the op.

[kcdc627]

Have you tried to loosen the bleed screw on the coolant tank, you may have air in the radiator from when you changed the t-stat.

[LuxoM3]

Sounds like the thermostat housing :)

it tends to be a slow leak... and against the popular will of mechanics on this board... you can't just bolt it back into place after changing the water pump or thermostat...

This is ESPECIALLY true of the aluminum thermostat cover...

In a nutshell... it doesn't leak when you are sitting still or cold... it DOES leak once the car is warmed up and pressure builds...

The solution?

Pull the thermostat housing off... get some nice silicone gasket stuff and well... simply goop up the orange gasket and thermostat o-ring.

----

As an aside... keep in mind your heater core also stores about 1 liter of coolant that only circulates when you turn the heater on full blast. Since it's winter 1 of 2 things will happen... you'll either be down a full liter (in that case your heater core was empty of coolant) OR you'll be OVER a liter (meaning your core was full).

You'll find the above 2 instances common especially if you've done any coolant work within the last few months.

Hope this was helpful.

[M3C]

What would be normal amount of coolant to add every given milage or time frame?
I know for engine oil it is normal to add up to 1 quart every 600-700 miles.

[///Mmmm, Donuts]

I know for engine oil it is normal to add up to 1 quart every 600-700 miles.

:confused Not unless you've got a rotary. You might want to get that engine checked out...

[slipstream]

I was getting this for about 6 months and couldn't figure it out. Then my rad blew. The connection for the large hose on the drivers side broke completely away (damn plastic):mad. I know you said you checked everything and couldn't find any leaks but you might want to recheck the rad. Ever since mine blew I did some research and I've found out that BMW rads are known to fail. It's kind of a when, not an if. BTW I had 90k on mine when it blew. How many miles on yours?