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View Full Version : Help please! Car overheats and leaks coolant when heater is on...


bimmerboy2051
12-09-2010, 07:50 PM
Hello everyone. It has been quite a while since I've been around these parts. My car is at it again, this time with another cooling system issue. It seems that when I turn my heater on, my car overheats and leaks coolant. Here is the rundown of how I determined this...

Yesterday afternoon I was stopped at a stoplight and I noticed smoke coming from the engine. I rolled the window down and it smelled of coolant. While this happened, I had my climate control on set to auto at 72 (which is what I always have it set at when it's cold out). The needle on the temperature gauge stayed right in the middle. I pulled over, shut the car off and inspected the engine bay. There was coolant sprayed/splattered everywhere (see attached pictures). I decided to risk it and drive home very carefully. However, before I started off, I decided to shut the climate control off. I drove home (15mi drive on the freeway in stop and go rush hour traffic) and the whole way there was no smoking and the needle stayed right smack in the middle.

Today, I drove around town and did some errands (with the climate control off) and everything was fine. When I got home, I parked the car in the driveway and let it idle. This time I turned the climate control on and turned the temperature all the way up and let it sit. After a few minutes or so the low coolant light came on, the needle started quickly going over to the right and coolant started leaking from underneath the car. I could also hear a bubbling or boiling sound coming from the expansion tank. I immediately shut the car off and let it sit for about half an hour. I turned the car back on (with the climate control off) and the needle was back in the middle. I drove around the block a few times and let it idle for a few minutes and the needle stayed in the middle and no leaking whatsoever.

Before all of this happened I also noticed on a few occasions that by having the heater on would cause the low coolant light to come on and when I would shut the heater off the light would go off.

Today I inspected the expansion tank to the best of my ability and found no cracks or anything. As a matter of fact, I just replaced the expansion tank about 6-8 months ago so it's fairly new. I don't think it would be the water pump either as this was just replaced a year or so ago. So, with this information, does anyone have any idea as to what this could be? Thermostat maybe? My car has 127K on the clock and I believe this is the original thermostat. As always, thanks so much everyone.

BDWREDZ
12-09-2010, 08:03 PM
Normally a bad thermostat will just get stuck open or closed, will not cause a leak. Where is the coolant leaking from, that is causing the burning smell?

bimmerboy2051
12-09-2010, 08:07 PM
Normally a bad thermostat will just get stuck open or closed, will not cause a leak. Where is the coolant leaking from, that is causing the burning smell?

I removed the splash guard and looked underneath the car. It seems to be leaking from the drivers side area but its hard to tell. Thats where I noticed it leaking from when I turned the heater on and the car was idling in my driveway.

bimmerboy2051
12-09-2010, 08:31 PM
Oh and one more thing...when I turned the heater on earlier today and let the car idle, I noticed the air blowing out from the vents was really not all that hot...just warm actually. Also, I noticed some dried coolant build up around the thermostat... (see attached picture).

ThreeTwoFive
12-09-2010, 08:55 PM
I bet its leaking from water pump or thermostat housing and the fan is throwing the hot coolant around.

Dave 330i
12-09-2010, 09:00 PM
A leaky heat exchanger core?

bimmerboy2051
12-09-2010, 09:29 PM
I bet its leaking from water pump or thermostat housing and the fan is throwing the hot coolant around.

A leaky heat exchanger core?

I guess my ultimate question would be, what would cause the car to overheat and leak coolant by having the heater on?

ThreeTwoFive
12-09-2010, 10:32 PM
I guess my ultimate question would be, what would cause the car to overheat and leak coolant by having the heater on?

Gasket leak over time depending on the cars age and mileage.
Cooling system overhaul is due on these cars roughly every 75,000 miles.

bimmerboy2051
12-09-2010, 10:38 PM
Gasket leak over time depending on the cars age and mileage.
Cooling system overhaul is due on these cars roughly every 75,000 miles.

Are you talking about the head or valve cover gasket? If so, this could cause the car to overheat by having the heater on?

Lbert
12-09-2010, 11:07 PM
The whitish stains shown on your pictures are coolant that has dried up. The coolant drips onto the belts and the belts splashes the coolant around the engine. Get a small mirror and look at the weep hole on the underside of the water pump. I have provide a picture for your benefit. It is also possible the leak maybe coming from the thermostat or both.

bimmerboy2051
12-10-2010, 10:59 AM
I know you guys are telling me where the leak is possibly coming from but I would really like to know why the car would overheat and leak coolant when the heater is running. What would cause that?

P_T
12-10-2010, 11:23 AM
First and foremost you need to find the source of the leak! When you turn the heater on it dirverts coolant to the heater core. Your light is on because the fluid level is low, and lower when you are pushing extra coolant to the core. Top the radiator off, drive the car with the heater full on, then park it and look for the steam. You must find and fix the leak first!

bimmerboy2051
12-10-2010, 03:49 PM
Ok guys. I think I may have discovered the problem. I did some more testing and looking around today and noticed a few things. First and foremost, I topped the coolant up. I did some more looking around under the hood and discovered three places where coolant was leaking from. The first place (see first picture) is where the smaller hose connects on the bottom of the expansion tank. It was loose. It seems this is where the coolant leaks from when the heater is on. It seems like some pressure gets built up and pushes the hose off a little bit which causes coolant to leak. The second place I noticed leak marks (see second picture) was on the underside of the thermostat. On the underside of the thermostat the coolant seems to be leaking out from a bolt or something. The last place I noticed leak marks was on the underside of the engine (see third picture). You can see a trail of dried coolant coming from higher up somewhere and settling down on the bottom of the engine, ultimately dripping off.

I pushed on the smaller hose on the bottom of the expansion tank really good and made sure the metal clamp was properly seated then went for a road test. During my road test, I kept the climate control off. After some driving, the temperature went to the normal 12 o clock position and stayed there for a while. Then something happened that I have never seen before and I have owned this car for nearly three years. The needle actually started going to the left towards the cold side then it would return back to the middle. It did this on three different occasions. I returned home and inspected underneath the car and from the top of the engine bay. No leaking whatsoever. I dont know if this means anything or not, but one thing I did notcie was that the hose from the lower radiator to thermostat was warm to the touch and the hose from expansion tank to thermostat was VERY hot...

I***8217;ve read in several places that if the temperature starts to get cold while driving then most likely it***8217;s the thermostat. The car does not overheat or leak coolant with the heater off. I don***8217;t want to jump to conclusions but it seems that if I turn the heater on, it causes pressure to build up and coolant leaks from around that hose on the expansion tank. Could this be because of a faulty thermostat? Nonetheless, I am going to change the thermostat. What do you guys think?

Lbert
12-10-2010, 09:53 PM
You are over working the problem. Find the source of the leak and things will fix itself as already mentioned by P T. If the thermostat, water pump, or hose is leaking, replace it.

bimmerboy2051
12-10-2010, 10:21 PM
You are over working the problem. Find the source of the leak and things will fix itself as already mentioned by P T. If the thermostat, water pump, or hose is leaking, replace it.

Yes I understand. But don't you just find it interesting how the car ONLY leaks coolant when the heater is used? Otherwise, no leaking whatsoever.

P_T
12-11-2010, 08:48 AM
Yes interesting problem, but the remedy is the same. Identify and repair each leak. You may find that you have a leak in the heater core hose. If there was a leak in the heater core you would have a strong antifreeze smell in the cabin and probably fluid on the floor.

Find you leaks, fix them and throw a thermostat in and go from there.

jburns
12-11-2010, 09:46 AM
I would say a faulty thermostat is causing the problems....pressure changes and all. Change the thermostat, fix the leaks and go over all the hoses and connections. Fill it back up, proper mix, bleed the system GOOD....and be done with it!! :thumbup:

smolck
12-11-2010, 03:44 PM
It would be my guess that your heater core has a clog in it or has failed. The leak could be coming from any one of a dozen places. You'll need to hunt that down the old fashioned way, with a flashlight.

bimmerboy2051
12-11-2010, 04:37 PM
Well...now the car just overheats...regardless of heater/climate control usage. No leaking though... Lower radiator hose to thermostat is not hot at all. Upper expansion tank hose to thermostat is VERY hot. Fan is relatively easy to spin when car is hot... Any ideas?

smolck
12-11-2010, 05:16 PM
Well...now the car just overheats...regardless of heater/climate control usage. No leaking though... Lower radiator hose to thermostat is not hot at all. Upper expansion tank hose to thermostat is VERY hot. Fan is relatively easy to spin when car is hot... Any ideas?

Yep, and it's good news too. Your thermostat is stuck closed. The lower hose not hot is the classic symptom. $60 and about 30 minutes and you are back in business. :thumbup:

jtb.baker
12-11-2010, 05:54 PM
I could be totally off, but Ill throw this in based on your second picture. I had a coolant leak that appeared to be coming from the thermostat or the water pump. Here is a link to my original post about the problem. http://www.bimmerfest.com/forums/showthread.php?t=451952&highlight=

You can see the pool of coolant in the first picture in my original post. Before I noticed it, it had pooled enough to leak down the side of the engine, get on the belts, and spray coolant all over. Just like your picture.

Due to the significant amount of coolant on the driver's side of the engine, I replaced the heater pipe and water inlet pipe. These are under the intake maniold and require the manifold to be removed. Paid a mechanic $600 to replace these pipes and the CVV and all hoses since he was already in there.

Leak still there. :mad: Turned out that the leak was coming from the bolt right above the water pump behind the pooling coolant. I believe the bolt connects the timing chain cover to the engine. I tightened the bolt and have not had a leak since.

bimmerboy2051
12-11-2010, 05:59 PM
Yep, and it's good news too. Your thermostat is stuck closed. The lower hose not hot is the classic symptom. $60 and about 30 minutes and you are back in business. :thumbup:

Ok. Gonna order the termostat then get that changed ASAP and I will report back to you guys. Thank you so much.

ThreeTwoFive
12-11-2010, 07:57 PM
Get it fixed because the problem won't go away on its own and will cause you more problems.

I'm chasing a coolant leak as well and I cannot find where it leaks from. All I know is that when I top it off and start driving low coolant light is on 5 minutes later.
I have a new radiator and expansion tank on order.
I haven't been able to see the leak itself, all I see is lots of coolant on my splash pad.
Pressure test and checking under the engine when the car is running did not reveal the source. I think it has to do with the level of the coolant and how hot it is.

bimmerboy2051
12-16-2010, 10:04 PM
Well everyone, I replaced my thermostat today and everything seems to be fixed. Hopefully it will hold. We will see. I now have heat coming out of my heater again thank goodness. Also, just thought I'd say, I did not use the special fan removal tool. I just used smolcks method and hit the wrench with a hammer to shock the nut loose. Though, I didnt hit it as hard as smolck does. Lol. Putting the fan back on with the shroud in the way was a b*tch. Theres my rant. Thanks everyone for the help.

serge_ua
12-17-2010, 03:02 PM
Let us know if the problem is gone for good! It seems that I have thermostat problem lately myself. And I can really feel it after moving from NC to Boston. If I start my car when it's cold and get on highway fast, the temp needle stays in the blue zone forever, and the cabin does not heat up! When it is 10 degrees outside, it is no fun! However, if i start with the city stop-and-go traffic, the needle gets to 12 o'clock pretty fast, and I get warm air from the vents. And I recently observed what you have described: the needle moved *to the left* from 12 o'clock until it touched the blue zone. It happened when I was driving on a highway after some city traffic. After reading your post and few others, it seems like I need a new thermostat. The car has 69K now, so it is about time, right? I am gonna replace a water pump while I am at it. I don't have any leaks now, so do i need new hoses? What do you guys think?

bimmerboy2051
12-18-2010, 11:43 AM
Let us know if the problem is gone for good! It seems that I have thermostat problem lately myself. And I can really feel it after moving from NC to Boston. If I start my car when it's cold and get on highway fast, the temp needle stays in the blue zone forever, and the cabin does not heat up! When it is 10 degrees outside, it is no fun! However, if i start with the city stop-and-go traffic, the needle gets to 12 o'clock pretty fast, and I get warm air from the vents. And I recently observed what you have described: the needle moved *to the left* from 12 o'clock until it touched the blue zone. It happened when I was driving on a highway after some city traffic. After reading your post and few others, it seems like I need a new thermostat. The car has 69K now, so it is about time, right? I am gonna replace a water pump while I am at it. I don't have any leaks now, so do i need new hoses? What do you guys think?

Yeah...I would replace the thermostat. The temperature needle at the 12 o clock posistion is where it should be at. Any movement once the car has gotten to normal operating temperature would most likely indicate foul play with the thermostat based off of my experience and what ive read. If your not objected to messing with removing the belt on the water pump the go ahead and do it. It's smart maintenance. Mine failed at around 90k. Both upper and lower hoses are about 20 dollars each. Why not. Autohausaz.com is a great place to buy.

serge_ua
12-18-2010, 06:14 PM
Yeah...I would replace the thermostat. The temperature needle at the 12 o clock posistion is where it should be at. Any movement once the car has gotten to normal operating temperature would most likely indicate foul play with the thermostat based off of my experience and what ive read. If your not objected to messing with removing the belt on the water pump the go ahead and do it. It's smart maintenance. Mine failed at around 90k. Both upper and lower hoses are about 20 dollars each. Why not. Autohausaz.com is a great place to buy.

Thanks Bimmerboy!