View Full Version : diagnose my problem... no heat, engine overheating

scott pruett
10-20-2008, 02:15 AM
Hey guys -

I'm kinda a noob w/ BMWs, but I figure this can't be too complicated. Diagnose this for me:

Symptoms: (1) My engine is overheating. No lights come on. I did get smoke/steam coming out of it tonight. Coolant levels are fine. Oil levels are fine. (2) My heater doesn't blow any warm air.

I assume I just need a new thermostat, but the overheating concerns me. Could the water pump be going bad too? Is there a way I can figure this out on my own?



10-20-2008, 02:18 AM
have you tried bleeding your radiator?

scott pruett
10-20-2008, 02:20 AM
I haven't...

10-20-2008, 02:29 AM
hmmmm i don't think it is your thermostat as those remain open when they break and your engine will get cold not hot. soooo..... I would say try bleeding the radiator like someone else said because it could have air in the system. But if it doesn't have air in the system then i am unsure and you may want to look into that water pump.

10-20-2008, 02:37 AM
hmmmm i don't think it is your thermostat as those remain open when they break and your engine will get cold not hot.

Sometimes the thermostat will stick closed, causing rapid overheating. How long does it take to over heat? 5 minutes? 20 minutes? Does your oil look OK? If it's discolored (milky), that could be a sign of a blown head gasket...

My first vote is water pump, however...

scott pruett
10-20-2008, 02:57 AM
It took about 20min @ 60-70mph @ ~45deg outside temperature to overheat & start steaming/smoking.

The oil looks okay, although I'm due for a change.

Is flushing the radiator an easy DIY job, or do I need to find a shop? The water pump was one of my thoughts as well...

10-20-2008, 03:07 AM
+1 on Will's suggestion

10-20-2008, 03:35 AM
search "burping" or "bleeding" the cooling system and follow the steps. Repeat the process several times to ensure all of the air escapes.

10-20-2008, 03:50 AM
Please help educate me on this... If he hadn't done any work on the cooling system (or at least he didn't say so...), why would he need to bleed the air out? Is there an underlying problem that allows excessive air into the coolant lines? It just doesn't make sense (but that's why I would like enlightenment).

Just from an engineering standpoint, the water pump not circulating properly would cause these symptoms. A thermostat locked in the closed or open position would not cause all the symptoms he is experiencing... Would an airlock in the coolant system cause all these issues simultainiously?

But I really don't know... just taking my best educated guess... (and trying to help!)

scott pruett
10-20-2008, 03:54 AM
Thanks guys.

yeah wolferj, I haven't done anything yet. I'm trying to educate myself before messing around and/or spending unnecessary $$.

10-20-2008, 04:23 AM
When I first got my car, it had a tiny hairline crack on the radiator next to the expansion tank. It wasn't big enough to show signs of any leakage, it only leaked when the engine temp was warm and even then, the coolant evaporated before you could see it. I experienced the no heat issue at the worst possible time(driving cross country through an ice storm).

As soon as I seen the needle begin to rise, I pulled over, let the motor cool down and added coolant. Did this a couple times during that trip until I finally read about bleeding the cooling system. As soon as I bled the cooling system, my heat returned. At that point, I didn't know that my radiator was cracked. I did however check my coolant level everytime I stopped for fuel and it continued to need topping off. Made it home with no problems, again topping off the coolant whenever possible.

Once home, I looked for leaks and found nothing. Drove the car for a couple thousand miles, everyday observing that the coolant level continued to drop. Friends, family and forum members all swore up and down that I had a blown head gasket. However the car continued to run fine, no smoke, no coolant/oil mixing. Still continued to drive it, topping off once a week. Eventually it got so bad that I was topping it off daily.

Two oil changes, almost 10k miles later, it still showed no signs of a blown head gasket. Nobody could explain where the coolant was going. One day a friend and I rigged up a pump with a fitting that threaded onto my radiator cap. I pressurized the system to about 10psi and listened for leaks. That's when i found the crack next to my expansion tank.

I was so cautious, that my car never once overheated. Even the time during my adventure across country when I bought the car, the needle only began to rise. The whole time I knew I had a problem, but I watched that needle like a hawk. I checked the coolant level EVERY DAY! When it dropped, I topped it off and bled it. I even got sprayed in the face with boiling hot coolant at one of our SoCal meets! But I still topped it off.

My point, even the tiniest of undetectable leaks can let coolant out which in turn leaves an air pocket. If let go long enough without bleeding, it'll eventually cause air-lock in your radiator and coolant will not be able to circulate. That's why your heat stops working, there's no coolant flowing through the heater core.

My suggestion, bleed the cooling system thoroughly and monitor the coolant level daily. It may take a few good bleeding sessions to remove all of the air. Repeat the process several times. If you continue to lose coolant, it's time to start looking for a leak. There's a couple plastic coolant lines that are known to crack. Also, your radiator could be leaking in an area that is not visible.

Perhaps you could rig up the same type of tool that I did to pressurize your radiator and listen for leaks. If you do that, I suggest doing it indoors because the hissing will be very faint. Good Luck, sorry for the long post.

10-20-2008, 04:37 AM

Thanks for your response. It helps describe what could be the underlying issue. As always, you give great feedback and share your knowledge. I learned something. Hopefully, so did others...


I would certainly take this course of action, as it may help determine the issue, or at least tell you what it isn't, and it isn't expensive...

Good luck.


scott pruett
10-20-2008, 02:55 PM
Jess - thanks! no need to apologize for a long post; that kind of info is golden. I'll give bleeding the cooling system a shot when I have time later today.

Anyone needing further info, this thread has a pretty straightforward how-to re: bleeding the system: http://318ti.org/forum/showthread.php?t=22203 (again, kudos to Jess)

James - thanks man, I appreciate the input.

10-20-2008, 06:04 PM
right now, the best you can do is get a CO level test done on the cooler water.

This will provide indesputable truth whether there is a comprimise in the headgasket/cyl head. From there you will need to look at it objectivley.

A compression test on each cyl, will tell you if you have a failed gasket by the cylinder top, as it will not hold pressure.

You can allso try a coolant system pressure test, to see it there are any abnormalities there.

Be aware the best (worst) time to see these types of problems are when the car is cold > hot. When hot, its pretty impossible to see anything, as everything expands ;)

From what i can see above,

Car steaming (majopr pressure build up) and no warm air (blockage before heater matrix = thermostat faliure? )

Please check the 2 hoses (into and out of) from the radiator are of equal´ish temp.

If not then it may be the thermo is stuck closed.

If the car was showing a major overheating then it may indicate a defective waterpump. But also a possible headgasket faliure.

Check water levels daily !
Check oil condition daily !
Get a CO level test / cyl comp test done.
Check temps of both hoses out of the rad.
Change as a precautionary measure, the thermostat
Get the car propperly bled.

also if you notice a thick sweet smelling WHITE exhaust smoke, that means your burning coolant.

scott pruett
10-21-2008, 03:57 AM
burped the radiator tonight... coolant was very low, got lots of bubbles. I'll see how things behave tomorrow. Heater is now pushing warmer air, so things are looking hopeful!

thanks again... will investigate other suggestions if needed.

10-21-2008, 05:18 PM
There are two main areas to watch for leaking coolant.

The first at the bottom of the expansion chamber like Jess described. The second is a hose fitting on the back of the engine that is known to break.

Replacing the latter is a good preventative measure, but the former is somewhat expensive.

If it's troubling you, have the system pressure tested and have them do UV leak detection. If there's a problem with air entering your system, those two tests will find it pretty quickly.

10-21-2008, 05:43 PM
The two plastic coolant fittings that are prone to failure are as follows:

"Y" fitting located on back of cylinder head between engine and firewall. This fitting is difficult to access but can be accessred easier by removing the valve cover. If doing so, you may want to purchase a new valve cover gasket and spark plug seals as well. The part is rather cheap, I think around 7 bucks.

And the other fitting located on the block underneath the lower intake manifold. This part requires removal of the upper and lower intake manifold. It's not as common to break, but should still be replaced. IIRC it costs about 15 bucks.

And a link to a great cooling system rebuild thread where those pictures were found, written by CirrusSR22:

11-01-2008, 12:08 AM
I have teh same problem. i change the water pump and thermostat.