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Discussion Starter · #1 ·
Okay, this is hard and I can’t wrap my head around it. My car has been through three thermostats and it’s still overheating. I replaced everything for the cooling system. Thermostat, water pump, expansion tank, upper/lower rad hose, radiator, fan clutch, belts and pulleys/ tensioner with the blue bmw coolant/ sensors. Not the one on the engine block though. After cooling system overhaul with genuine/OEM parts I had about 1000 miles of fine driving with my car overheated out in philly. I was near a friends and replaced the thermostat with one from the jyard and the car worked fine and got me home about 4 hours away. It was a motorad and 2018 date code on it. Before anyone asks why I didn’t get a new one none were in stock and I didn’t have the luxury of waiting for a new one to come in. Well about 2000 miles later my cooling light started going on and off then my car overheated after about 40 minutes of highway driving. Got it towed home and replaced it with another new Wahler thermostat. Car didn’t overheat and I drove it for about 40 minutes around town around 40-50 mph. Cooling light came on and off although. I bled the system again and it was off. Wouldn’t come on. Well after about 15 minutes off highway driving it was coming on and off and 25 minutes later the car overheated. After letting it cool down for 15 minutes I let it idle for jokes and drove it one minute and it didn’t overheat but cooling light was going on and off. No coolant leaks or anything. I am stumped. I know it’s possible to get defective parts but I’m totally lost at this point. I replaced everything in the engine besides the vanos refresh but that has nothing to do with cooling. Where do I go from here? I plan on a compression test but would a cracked cylinder head or bad head gasket be setting off the cooling light? No I don’t believe so and that doesn’t seem to be the issue at hand. I did check the thermostat fuse and noticed it was burnt around the edges of it and replaced it before leaving with another 20 amp fuse.
 

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2016 340i xD 6-spd
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After all that work, I'd repeat bleeding. You don't have to say you bled it well...I know you did. Our system is hard to bleed for many. Don't be ashamed! :)

If you found a burnt fuse, run that down...you might have a short in some wire rubbing against metal for 20 years?

Also, you may have a leak, allowing air in, coolant out, so you'd get warning lights and overheat...the wp can cavitate with air in it and not pump. Check through your intake mani to see if your hard pipes are leaking...

...always good to mention model car and mileage

Also, everyone here, me included, is a moron...why else would you want a 20 year old car? Be careful how you word things--this isn't FB. :)
 

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Discussion Starter · #3 ·
After all that work, I'd repeat bleeding. You don't have to say you bled it well...I know you did. Our system is hard to bleed for many. Don't be ashamed! :)

If you found a burnt fuse, run that down...you might have a short in some wire rubbing against metal for 20 years?

Also, you may have a leak, allowing air in, coolant out, so you'd get warning lights and overheat...the wp can cavitate with air in it and not pump. Check through your intake mani to see if your hard pipes are leaking...

...always good to mention model car and mileage

Also, everyone here, me included, is a moron...why else would you want a 20 year old car? Be careful how you word things--this isn't FB. :)
2004 bmw e46 330xi. Just frustrating doing all of this preventative maintenance for this to happen. Electrical wise. What could be the problem? Can that cause warning cooling light?
 

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I'm not smart, but here goes anyway.
I'd have expected bleeding issues to become evident more quickly. But yes, how did you bleed?
What kind of driving were you doing when it overheated? Maybe electric fan?
So no coolant leaks? Is it possible someone used stopleak?
 

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Discussion Starter · #5 ·
I'm not smart, but here goes anyway.
I'd have expected bleeding issues to become evident more quickly. But yes, how did you bleed?
What kind of driving were you doing when it overheated? Maybe electric fan?
So no coolant leaks? Is it possible someone used stopleak?
Is it possible for an air bubble to overheat the car after 40 minutes of driving?
 

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2005 330 Cic ZHP
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2 thoughts come to mind.

1) You can use the OBC diagnostic menu to see your coolant temp in real time (search for "secret menu" for instructions). This would give you a way to see what the coolant temp is really doing as you drive...or possibly help identify a bad sensor.

2) If I'm reading your description of the cooling behavior correctly, it appears the problem happens (mostly) at road speeds and not around town stop-n-go. Maybe there's an issue with the new fan clutch? I don't know exactly how the E46 fan clutch is supposed to behave since I have a 3-pedal, but I can hear the fan clutch on my 4Runner releasing as engine RPMs climb (to avoid over driving the fan?). Maybe your fan clutch is completely disengaging at road speeds (above a certain RPM) and unassisted air flow isn't enough to to maintain temp?
 

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You say it "overheated". What, exactly do you mean by that? The gauge went into the red? A warning light came on? You lost coolant? Something else?

Have you ever actually CHECKED the coolant temperature while driving?
 

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I suggest recoding the temp gauge to help with seeing how hot the engine actually is, rather than seeing the huge buffer zone which will show right in the middle until it is overheating. Or as mentioned use the OBC to see the temps. When you refer to the overheating light, you mean the one that comes on when the gauge hits red and not the low coolant light, correct?
These cars are difficult to bleed all the air out and if you have leaks it can cause air to get back in, especially if the tank runs out.
If you didn’t replace the temp sensor with genuine or OE I’d try that, cheap sensors cause more problems.


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2002 325xi Touring
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I am definitely not smart about anything except the history of bikinis but here goes…

That temperature sensor on the back of the engine block is possible to replace without removing the manifold. Working up a sequence of extensions and swivels and using your fingers as eyes gets you there. I’ve done it myself, easy as pie.

If you’ve got trapped air in your coolant system (for me this resulted in no cabin heat) – I wrestled with the problem for months checking all suspect parts and trying every which way of bleeding a dozen times. It wasn’t until I blew air and water up through the engine block through the lower HCV pipe that I suddenly somehow agitated and dislodged about a quart volume of stubborn trapped air and my cabin heat came back.

And this is more a general question to the forum than a suggestion because I want to prove how not smart I really am –

How do you know your engine is overheating? Because your gauges SAY so – or because it actually IS? What if you pointed one of those infrared laser thermometers at your engine block or hoses and it said your engine temp was fine?
 

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What are you referring to when you say "cooling light"? Is it the yellow coolant level light?? or is it the red light near the temp gauge?

Is the car overheating in traffic, or at a stoplight after a highway run? If so, your fan clutch AND/OR your Aux fan is not working. You should make sure both are working. I recently had this issue on my X5..bothe were bad.

Your symptoms also suggest an obstruction as a possibility...Any chance anybody ever used "stop-leak" or something similar? You should consider a backflush of your system AND your radiator and see what comes out and what flow looks like. I have personally pulled chunks of hardened stop-leak the size of my thumb out of an M54 cooling systems.

You should learn to unlock the hidden menu on the cluster and drive around with your temps shown on the cluster at least while you are figuring this out. (test #7)
 

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How do you know your engine is overheating? Because your gauges SAY so – or because it actually IS? What if you pointed one of those infrared laser thermometers at your engine block or hoses and it said your engine temp was fine?
That’s kinda what I was getting at, a new genuine/oe sensor and see what the OBC is showing. The gauge is basically useless as it shows dead center up until it’s way over heated. OP said the light was going off and on, which the light comes on when it hits the red zone, unless it’s right at the point where it comes on and is just flickering until it jumps up 1 degree to keep the light on steady, then it sounds like a sensor issue.
You can confirm the sensor is working by checking the engine block with an IR thermometer when the engine is cold and check it with the OBC, and again when it warms up to see if it’s any where near close.


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A good way to replace temp sensor on rear of engine is to buy a cheap 22m open end wrench and cut it off making a stubby 22mm....You don't need much leverage to remove the sensor.
 

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2001 330i (pre-facelift)
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You say it "overheated". What, exactly do you mean by that? The gauge went into the red? A warning light came on? You lost coolant? Something else?

Have you ever actually CHECKED the coolant temperature while driving?
My thoughts exactly. Sensors can go bad. Tossing parts at the car is no substitute for a proper diagnosis.
 

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Discussion Starter · #15 ·
What are you referring to when you say "cooling light"? Is it the yellow coolant level light?? or is it the red light near the temp gauge?

Is the car overheating in traffic, or at a stoplight after a highway run? If so, your fan clutch AND/OR your Aux fan is not working. You should make sure both are working. I recently had this issue on my X5..bothe were bad.

Your symptoms also suggest an obstruction as a possibility...Any chance anybody ever used "stop-leak" or something similar? You should consider a backflush of your system AND your radiator and see what comes out and what flow looks like. I have personally pulled chunks of hardened stop-leak the size of my thumb out of an M54 cooling systems.

You should learn to unlock the hidden menu on the cluster and drive around with your temps shown on the cluster at least while you are figuring this out. (test #7)
When I say cooling light I was referring to the yellow one going on and off sporadically. Thank you all for the insight. I plan on taking about all the hoses and inspecting them and reinstalling everything then. Is it possible for the thermostat connector to be bad and cause overheat?
 

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'03 325iT Mystic Blau
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When I say cooling light I was referring to the yellow one going on and off sporadically. Thank you all for the insight. I plan on taking about all the hoses and inspecting them and reinstalling everything then. Is it possible for the thermostat connector to be bad and cause overheat?
If that's all your issue is then it's not overheating you're having an issue with. All that indicates is low coolant level and could be just a bad level sensor.


<---Not smart, but felt compelled to comment anyway.
 

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When I say cooling light I was referring to the yellow one going on and off sporadically. Thank you all for the insight. I plan on taking about all the hoses and inspecting them and reinstalling everything then. Is it possible for the thermostat connector to be bad and cause overheat?
The thermostat is a mechanical device, the connector does nothing except heat it up slightly so the ECU can control the temp by a few degrees. Even disconnected it shouldn't overheat. Also these thermostats usually fail open.
You can put the temperature reading up on the gauge cluster doing DIY: E46 hidden OBC functions . Do this next time you drive and see how the temp gauge reacts. Could be a faulty sensor?
 

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2002 325xi Touring
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A good way to replace temp sensor on rear of engine is to buy a cheap 22m open end wrench and cut it off making a stubby 22mm....You don't need much leverage to remove the sensor.
You remind me – I used my “BMW Oxygen Sensor Removal Tool, 22mm, 3/8 in. drive”.

It was nice discovering a perfect secondary use for this tool.

 

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Discussion Starter · #19 ·
When I say cooling light I was referring to the yellow one going on and off sporadically. Thank you all for the insight. I plan on taking about all the hoses and inspecting them and reinstalling everything then. Is it possible for the thermostat connector to be bad and cause overheat?
Let me rephrase. The yellow cooling light did come on and off before the temp gauge displayed it overheating.
 

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back in #4, I asked about driving conditions when this happens.
Maybe it really is overheating. I'd want to confirm that.
 
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