Overheat problems z3 1.9 1997

[micfor]

Hi my name is Michal, and i live i Norway. My Z3 is inherited, so it means a bit to me - in addition to the fact that it is a nice car

Milage is 247000km.

Recently i have had overheating problems that i can't figure out, hopefully someone out there can?

I have replaced or tested all parts thinkable; radiator, water pump, taken out the thermostat, flushed the hoses and engine, aired the cooling system, added cleaning chemicals to the system. Still it is overheating after some time, and pressure seems to be building in the system. Regarding possible top gasket leak, there is no sign of white smoke from exaust, no grey colour on oilpin og top lid, no exhaust smell from the cooling water. Fan runs, heater Works only occationally...

The problem occurs both when driving at low, high speed or ideling after 5-6km og 20-30min. Sometimes (not always) a lot of water has to be replaced. When hot and opening the air screw, sometimes i have my own private "geysir" blowing from radiator.....

Thankful for any tips...

Michal

[shogun]

Hi Michal, could be a blown headgasket from the described symptoms. To confirm exhaust gases inside the cooling system (gasket failure, cracked head or block) use a chemical tester and make a cylinder compression test . Here are the steps described and also a youtube
https://www.2carpros.com/articles/he...ket-blown-test

[micfor]

Thanks, I will do these tests! I also fear this is the problem, but is it not strange there is no white exhaust, no "white stuff" in oil pin or cap?

[shogun]

Before you throw more expensive parts into the car just on assumption, better make first a cylinder compression test, chemical test and a coolant pressure system test (in case you have a leakage somewhere. After these results are known, you know what to do next.
A blown headgasket will not be the end of the engine, can be repaired, or search for a used engine.

[Vintage42]

... Recently i have had overheating problems that i can't figure out... I have replaced or tested all parts thinkable... Still it is overheating after some time, and pressure seems to be building in the system... the problem occurs both when driving at low, high speed or ideling after 5-6km og 20-30min. Sometimes (not always) a lot of water has to be replaced...

Did the overheating begin before or after you worked on the engine? If it began after your work, it is possible that you did not bleed the system properly. Your symptoms are consistent with air remaining in the head.
Here's a collection of posts on bleeding the cooling system:
https://www.bimmerforums.com/forum/s...6#post29898336
https://www.bimmerfest.com/forums/sh...d.php?t=788246
http://forums.bimmerforums.com/forum...3#post26553723
http://www.bimmerforums.com/forum/sh...8#post28814738

I would be concerned that the many extended overheatings that you describe may have done harm to the head. You said "occurs both when driving at low, high speed or ideling after 5-6km og 20-30min." I think the engine should be shut off as soon as the needle moves toward the red zone.

[BimmerBreaker]

As the heater works intermittently, I think Vintage may be correct - it doesnt sound bled correctly

I disagree that it has caused damage though - damage to the engine does not occur until the needle is firmly in the red. I see a lot of cars overheating that dont suffer permanent damage. And usually HG leaks make themselves known in other ways like causing the engine to run poorly

Bleed it correctly and go from there

[Vintage42]

... damage to the engine does not occur until the needle is firmly in the red...

He did not mention what the needle did. But he did say "occurs both when driving at low, high speed or ideling after 5-6km og 20-30min".
That is a lot of distance and minutes to be running after he could tell it was overheating.
Question: When the engine overheats, can the needle rise but stabilize still in the green? Or does overheating inevitably progress into the red? And how long can the needle stay in the red before damage is done? Is it not best to shut the engine off before even reaching the red?

[nevan]

Did the overheating begin before or after you worked on the engine? If it began after your work, it is possible that you did not bleed the system properly. Your symptoms are consistent with air remaining in the head...

As Vintage and Bimmer mentioned, I would start from here also.

I'm also curious, what triggered you to start the cooling service? Did you have any overheating symptom before? If so, what kind?

[BimmerBreaker]

Depending on why the car is overheating in the first place, it is very possible for the overheating situation to "stop" at a certain threshold and maintain a high temp, or in some cases even cool back down. Sometimes they have a coolant flow issue so running them at a certain RPM will cool them, but as soon as you stop to idle, temps will creep back up...

If its a runaway overheating situation it absolutely should be shut off as soon as possible. For me I look at a few factors to determine if I shut an engine off and when during an overheat situation - first is how hot it currently is, obviously; second is how quickly the temperatures are rising, faster they rise the sooner I will shut it off; and lastly is any known issues with the cooling system, if its a failed water pump for instance, I will shut off once its basically in operating temp knowing that "nuclear" is not far behind but a small pinhole leak in a hose, I will let it run much longer

For me, I can't just shut off every engine that goes above TDC because I need to diagnose overheating issues. On some rare occasions, that can only be done with the engine at operating temp. For example I have an E36 M3 at my shop now, came in for overheating issues. It pressured tested perfectly, which is a little unusual for an overheating car (MOST of the time, its a leak). Ended up being a thermostat that was failed and stuck closed (the pin fell out, allowing the sprung thermostat mechanism to go off-center, binding against the engine block) - I was only able to diagnose this by letting it run up to operating temp and observing that the upper radiator hose was empty and not pressurized. In this case, during my testing, the car exceeded TDC but did not go past the 3/4 mark line. When the customer was driving the car, it got into the red, which is when he shut it down. It now has a new radiator, expansion tank, water pump, thermostat, thermostat housing and 4 main hoses, and it is holding temperature perfectly and compression has not changed at all (this is a regular customer of mine, so I have compression tested his motor before).

I'm not saying "Drive your car in the red, it's fine" what I am saying though, is there is no need to panic just because the needle has moved past TDC. TDC encompasses a huge range of operating temperatures, and above TDC is outside the realm of "normal" operation, but it isn't cause for immediate panic. If I had a dollar for every time an M54 came into my shop in the RED, but left after some minor cooling system work and the engine was still fine, well... I could afford a good M54B30! That's not to say a few haven't been bad... the customer who tried to DRIVE IT HOME IN THE RED OVER 20 MILES... did not fare as lucky as the customers who shut it off as soon as it was in the red (even if some of those in the latter group let it cool a mere few minutes, then drove it again until it was in the red, pulled over and let it cool down and repeated this dance until they made it home)

Of course, knowing how your cooling system works, and where the temperature sensor is located, also helps... With all this being said, for most owners, I do advise that if the car is overheating at all to shut it down. It's not worth the risk if you don't know what you are doing. But, no need to immediately go shopping for replacement engines just because the needle moved above TDC.

[Vintage42]

Though it has been mentioned in many posts, it is worth repeating in this thread, that the coolant gauge's TDC is a comfort feature to tell you the temperature is within a wide range of normal.
The needle stays at TDC from ~170F to whenever overheating begins, which is ~225F.
After I installed a good new thermostat, my cooling system maintained a constant 206F according to a console mounted ScanGauge.
When the needle starts moving past TDC, the coolant is getting hotter than it should.
At that point, driver needs to make a decision.

[micfor]

Did the overheating begin before or after you worked on the engine? If it began after your work, it is possible that you did not bleed the system properly. Your symptoms are consistent with air remaining in the head.
Here's a collection of posts on bleeding the cooling system:
https://www.bimmerforums.com/forum/s...6#post29898336
https://www.bimmerfest.com/forums/sh...d.php?t=788246
http://forums.bimmerforums.com/forum...3#post26553723
http://www.bimmerforums.com/forum/sh...8#post28814738

I would be concerned that the many extended overheatings that you describe may have done harm to the head. You said "occurs both when driving at low, high speed or ideling after 5-6km og 20-30min." I think the engine should be shut off as soon as the needle moves toward the red zone.

Work on the car startet after overheating problem occured. Have also bled the car according to instructions with front lifted. Bubbeles "never" stops, and as temerature rises bubbels becomes "geysir"

- - - Updated - - -

Work on the car startet after overheating problem occured. Have also bled the car according to instructions with front lifted. Bubbeles "never" stops, and as temerature rises bubbels becomes "geysir"

- - - Updated - - -

As the heater works intermittently, I think Vintage may be correct - it doesnt sound bled correctly

I disagree that it has caused damage though - damage to the engine does not occur until the needle is firmly in the red. I see a lot of cars overheating that dont suffer permanent damage. And usually HG leaks make themselves known in other ways like causing the engine to run poorly

Bleed it correctly and go from there

Have bled the car according to instructions with front lifted. Bubbeles "never" stops, and as temerature rises bubbels becomes "geysir"

- - - Updated - - -

He did not mention what the needle did. But he did say "occurs both when driving at low, high speed or ideling after 5-6km og 20-30min".
That is a lot of distance and minutes to be running after he could tell it was overheating.
Question: When the engine overheats, can the needle rise but stabilize still in the green? Or does overheating inevitably progress into the red? And how long can the needle stay in the red before damage is done? Is it not best to shut the engine off before even reaching the red?

Needle stays stable in green for 15-30 min, then moves quickly to red

[micfor]

As Vintage and Bimmer mentioned, I would start from here also.

I'm also curious, what triggered you to start the cooling service? Did you have any overheating symptom before? If so, what kind?

First repair on the cooling started last year, With New radiator and expantion tank. I think the expantion tank sprunk leak, maybe there was some unwanted pressure in the system already? I do not know for sure. Then this year it started to overheat again, after a year of normality.

[Vintage42]

Work on the car startet after overheating problem occured...

First repair on the cooling started last year, With New radiator and expantion tank. I think the expantion tank sprunk leak... Then this year it started to overheat again, after a year of normality.

... Sometimes (not always) a lot of water has to be replaced... Bubbeles "never" stops, and as temerature rises bubbels becomes "geysir"........

It is possible that the first overheating a year ago warped the head which compromised the head gasket, causing a slow loss of coolant that was not noticed until overheating started again. The head gasket would also the the source of bubbles. Have the radiator tested for combustion gas.

[BimmerBreaker]

Have bled the car according to instructions with front lifted. Bubbeles "never" stops, and as temerature rises bubbels becomes "geysir"

If it didnt stop having bubbles come out, it isnt fully bled yet. Have you pressure tested it to make sure there are no leaks?

[micfor]

Thanks for helpful input, will do tests this weekend and post results