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E34 (1989 - 1995)

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  #1  
Old 01-26-2013, 04:09 PM
artemyk artemyk is offline
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Help diagnosing overheating problem (M20)

Dear forum members,

If anybody could help me diagnose an overheating problem, I would appreciate it endlessly. I have a 1990 525i, aka E34 with an M20 engine.

Let me give a bit of background. I was out of the country for a while and recently returned. The 'Coolant level' message was on in the car, but I foolishly ignored it for several days. Then, I was giving a friend a jump, and left my car on idle for a good 20 min. After that, as I was driving uphill toward a stoplight, the car started acting extremely strange, going into high RPMs --- I even depressed the clutch all the way and the RPM did not drop below 2000! ( I really can't explain that ). I then noticed the temperature gauge was maxed out and I promptly turned the car off. After that, the car wouldn't start for a good minute or two. When it finally started I parked it ASAP, let it cool down for an hour, got some 50/50 coolant and filled her up (the reservoir tank was empty at that point).

Since then, the car has continued to overheat. This is especially prominent during highway driving. If, while driving, I turn on the heater and turn it up to max, it blows hot air and the temperature gauge quickly comes down to the halfway mark.

I have since bled and re-bled the coolant system. I do this by running the engine and the cabin heat on max, opening the thermostat bleed screw and the radiator bleed screw, pouring in coolant to the top of the reservoir until coolant runs clear from the thermostat bleed screw, closing the thermostat bleed screw, continuing to pour it in until the radiator bleed screw runs clear with coolant (no bubbles). I've done this with cold and warmed up engine, parked flat and at an uphill incline, both engine running and not-running-but-heater-working. It doesn't seem to be fixing the problem, however.

The most pertinent facts seem to be that 1) I tend to overheat on the highway and 2) the cabin heating system is definitely working and is effective at clearing heat away from the engine. So, I am guessing the problem is one of the following:

1) An air bubble which is *still* trapped around the thermostat. In which case, more bleeding? Maybe drain the whole system and pour it back in?

2) Faulty thermostat, which is failing to start sending coolant through the radiator once the engine heats up. Though I find it strange that the thermostat would break when all this started with the coolant level being low and having to refill it.

3) Radiator clogged

Is there some other likely explanation for this? Specifically, a) could the water pump be broken? (would it be possible in that case that the cabin heating system would work but cooling-through-the-radiator not?) and b) could I have these symptoms if I was leaking coolant? (keep in mind I get the overheating even if I have just topped off the reservoir tank... )

Thanks greatly!
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  #2  
Old 01-26-2013, 04:16 PM
_Ethrty-Andy_'s Avatar
_Ethrty-Andy_ _Ethrty-Andy_ is offline
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highly likely that you have blown your head gasket. the M20 engines are amoung the more bullet proof BMW engines, but sounds like you severely overheated it. you went from a small problem of low coolant to a much bigger problem.

My educated guess is that it is your radiator was cracked, and overheating it made it worse. the thermostat on the M20 engine is designed to fail open so unlikely to be that, though just because something is designed one way doesnt mean it always works that way. highly unlikely to have damaged the water pump.

You will now be changing a headgasket too, so you will have to check the head for cracks or you will be wasting your time.

not only on BMWs, but on all cars, NEVER ignore anything to do with cooling system issues.
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  #3  
Old 01-26-2013, 04:23 PM
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Youve done in your HG.

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  #4  
Old 01-26-2013, 04:39 PM
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BMR_LVR BMR_LVR is offline
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Sorry to hear you're having problems.

I agree that you have likely blown the HG. It is a difficult DIY if you've never done it yourself and requires special tools if I'm not mistaken. It is an expensive fix if you have a mechanic do it.

I would recommend that you do a compression test or have it done. You can also get some kits at auto parts stores that will check for products of combustion in your coolant. These tests should be able to confirm the status of the HG. If your HG is blown, you will have a decision to make regarding fixing it, parting it out or salvaging it.

If your HG is good by some miracle, then I would highly recommend a full coolant system overhaul. It is not a difficult DIY and parts run $500-$600.

Good luck.
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  #5  
Old 01-26-2013, 04:48 PM
_Ethrty-Andy_'s Avatar
_Ethrty-Andy_ _Ethrty-Andy_ is offline
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if it is indeed blown, advise just buying another reputable M20 and put that in. why bother doing a headgasket when you can pick up a whole M20 for $200 tops
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  #6  
Old 01-26-2013, 04:51 PM
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BMR_LVR BMR_LVR is offline
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Quote:
Originally Posted by _Ethrty-Andy_ View Post
if it is indeed blown, advise just buying another reputable M20 and put that in. why bother doing a headgasket when you can pick up a whole M20 for $200 tops
truth
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Quote:
Originally Posted by noego View Post
It's Deja Poo - as in, I've heard this **** before.
Steve

Calypso Red 1992 525i with 200K miles

1991 735i - Sold
1992 525i - Sold
1995 325is - Sold
2000 528i - Sold

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  #7  
Old 01-26-2013, 04:54 PM
artemyk artemyk is offline
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Thanks guys for the really fast responses.

A blown headgasket was my worst fear, though I didn't realize how likely it was.

Is there a good way to diagnose a blown HG on this car, beyond taking her to a shop? I will check more tomorrow (its dark outside now), but the exhaust smoke does not seem cloudy, I didn't find any milky residue under the oil cap, and generally (besides the overheating unless I have the heater on) the car is running pretty smooth.
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  #8  
Old 01-26-2013, 05:10 PM
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_Ethrty-Andy_ _Ethrty-Andy_ is offline
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Quote:
Originally Posted by artemyk View Post
Thanks guys for the really fast responses.

A blown headgasket was my worst fear, though I didn't realize how likely it was.

Is there a good way to diagnose a blown HG on this car, beyond taking her to a shop? I will check more tomorrow (its dark outside now), but the exhaust smoke does not seem cloudy, I didn't find any milky residue under the oil cap, and generally (besides the overheating unless I have the heater on) the car is running pretty smooth.
you may be lucky, but pretty rare for an engine with a 20 year old gasket to survive that. it could even just be a small crack. does the exhaust smell sweet? (WARNING: dont put your nose to the tail pipe, just general area for no more than 5 seconds, harmfull gases there)
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  #9  
Old 01-27-2013, 01:35 AM
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BMWFatherFigure BMWFatherFigure is offline
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See if you can get the radiator 'sniffed' by the gas detector unit (looks a bit like a battery SG tester). It detects combustion gasses in the coolant. Dunno what a HG costs to fix where you are - here about $600 in parts plus labour (for me DIY). You must decide if the motor is worth keeping or ditching. Only you know that.
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  #10  
Old 01-29-2013, 10:41 PM
paperplane94 paperplane94 is offline
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There should be slew of tests that you can do, not only testing the exhaust gases. Look up some cheap testing methods so you will find an answer.
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  #11  
Old 01-29-2013, 11:07 PM
artemyk artemyk is offline
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I actually went and got a block tester kit from AutoZone, the one where you put some blue liquid in a baster-looking thing, suck up some air from the radiator overflow tank, and watch for color changes. I had some a bit of difficulty doing this test (mainly because it would suck up all the air from the tank), but doing it to the best of my abilities (and repeating 3 times) it came up negative (no color change). In addition, I see no bubbles in my radiator while the car is running.

I am really starting to think it might be a HG in any case, however. There does seem to be a subtle sweetness (if you excuse the wine-label terminology) to my exhaust, and the overheating problem is getting worse. I unfortunately don't know other cheap testing methods (besides checking for oil or combustion gases in coolant, for coolant in oil, or for the smell of the exhaust), so if you can suggest anything it would be appreciated. My next step will be to talk to a very knowledgeable friend-of-a-friend, and -- failing any insight from him -- take it to a shop to do a compression test.

Thanks again
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  #12  
Old 02-07-2013, 10:46 PM
artemyk artemyk is offline
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Hi all,
I ended up getting a compression test done and it also came up fine. It seemed like it was time for action so I started out by putting in a new thermostat and that actually seemed to fix it. Probably what I should have started with!
Thanks again for all your help,
-a
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  #13  
Old 02-07-2013, 11:56 PM
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BMWFatherFigure BMWFatherFigure is offline
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I was just about to suggest throw the 'stat away for a short term test. Now get the rest of the cooling system serviced. BTW why did you think the HG was bad when the most meaningful test came up good? (Funny smells are not 'meaningful tests')
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  #14  
Old 02-08-2013, 12:28 AM
///Brillantrot ///Brillantrot is offline
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Glad to hear that you likely solved the problem. Before I read your last post, I was going to make a suggestion... it may still be relevant. Reset your ECU. Might sound a little too simple but hey, it often is, isn't it? It sounds like you drove for a considerable amount of time with very little to no coolant and correspondingly high engine temps. This driving environment was relayed to the ecu and your vehicle tried to respond accordingly. By the time you refilled the coolant, your ecu was "confused" and not dealing with engine temp information in the same way it would've been, had the period of unusually hot engine conditions not occurred. Technically speaking, it was "out of whack." An example of how it might respond would be the failure of your fan to engage at the appropriate time/temp. I'm pretty sure (not being familiar with the M20 or having directly dealt with this specific issue) that your ecu could impact your engine's temperature in a number of ways. And, all of that being said, nothing could be easier than resetting it and eliminating that as the issue if it doesn't help. Did you happen to disconnect the battery when you replaced your thermostat? Anyway, if this problem happens to resurface, go ahead and do a reset (I'd actually do it regardless). If it doesn't fix the problem, you've spent no money and almost no effort doing it (tip if you're married: if you end up having to do this and it is successful, wipe a little engine grime/grease on yourself and walk into the house feigning exhaustion... you ought to score a nice dinner out of "working so hard" and fixing the car). Good luck man, hope the new thermostat continues to do the trick!
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  #15  
Old 02-08-2013, 07:31 AM
samsonnyc samsonnyc is offline
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Why did you think this was a HG issue in the first place ?
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  #16  
Old 02-08-2013, 07:51 AM
samsonnyc samsonnyc is offline
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Quote:
Originally Posted by ///Brillantrot View Post
Glad to hear that you likely solved the problem. Before I read your last post, I was going to make a suggestion... it may still be relevant. Reset your ECU. Might sound a little too simple but hey, it often is, isn't it? It sounds like you drove for a considerable amount of time with very little to no coolant and correspondingly high engine temps. This driving environment was relayed to the ecu and your vehicle tried to respond accordingly. By the time you refilled the coolant, your ecu was "confused" and not dealing with engine temp information in the same way it would've been, had the period of unusually hot engine conditions not occurred. Technically speaking, it was "out of whack." An example of how it might respond would be the failure of your fan to engage at the appropriate time/temp. I'm pretty sure (not being familiar with the M20 or having directly dealt with this specific issue) that your ecu could impact your engine's temperature in a number of ways. And, all of that being said, nothing could be easier than resetting it and eliminating that as the issue if it doesn't help. Did you happen to disconnect the battery when you replaced your thermostat? Anyway, if this problem happens to resurface, go ahead and do a reset (I'd actually do it regardless). If it doesn't fix the problem, you've spent no money and almost no effort doing it (tip if you're married: if you end up having to do this and it is successful, wipe a little engine grime/grease on yourself and walk into the house feigning exhaustion... you ought to score a nice dinner out of "working so hard" and fixing the car). Good luck man, hope the new thermostat continues to do the trick!
Adaptations on our ecu comprise only 10% of the car's behaviour, and are only about optimising performance. The adaptations are not about maintaining normal behaviour. And optimisations are more for general drivability and gear shift points for automatics, and not for engine heat response.

So I must disagree with pretty much all that you've said here.

And the electric fan's has is activated by the radiator coolant sensor. The ecu is not involved.

Last edited by samsonnyc; 02-08-2013 at 07:59 AM.
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  #17  
Old 02-08-2013, 08:33 AM
samsonnyc samsonnyc is offline
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Quote:
Originally Posted by artemyk View Post

Since then, the car has continued to overheat. This is especially prominent during highway driving. If, while driving, I turn on the heater and turn it up to max, it blows hot air and the temperature gauge quickly comes down to the halfway mark.
Doesn't this mean that its NOT a hg or cracked head ?
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  #18  
Old 02-08-2013, 08:42 AM
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Quote:
Originally Posted by _Ethrty-Andy_ View Post
if it is indeed blown, advise just buying another reputable M20 and put that in. why bother doing a headgasket when you can pick up a whole M20 for $200 tops
+1 on that, I may be headed that rout myself
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Old 02-08-2013, 10:51 AM
artemyk artemyk is offline
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I was strongly suspecting the head gasket because ---
* I suspected I overheated it pretty bad ... I had it running on idle for 30m when this happened (was trying to charge my friend's battery)
* knowledgeable people on here told me that it was likely to be the HG and that the M20 tstat is designed to fail open
* another mechanic I talked with told me I cracked the head

Seeing the block tester come up negative did reassure me some. But then I started wondering if I was doing it exactly right, if perhaps the leak was not happening at the temps/RPMs I tested it at but instead others, etc. Read enough Internet and it starts to seem there are exceptions and special cases to everything.

I should add that, prior to this, I had no experience under the hood beyond checking and changing the oil. So this has been a learning experience to say the least. If I was a tad more comfortable under there and had known just how easy it actually is to swap out the tstat, I probably would have started with that.
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  #20  
Old 02-08-2013, 10:54 AM
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BMR_LVR BMR_LVR is offline
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I'm glad you got it resolved, it was something so simple, and mostly, that your HG did not fail
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Most problems are usually something simple !

Quote:
Originally Posted by noego View Post
It's Deja Poo - as in, I've heard this **** before.
Steve

Calypso Red 1992 525i with 200K miles

1991 735i - Sold
1992 525i - Sold
1995 325is - Sold
2000 528i - Sold

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  #21  
Old 02-08-2013, 11:00 AM
artemyk artemyk is offline
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Me too! You have no idea... ;-)
BTW, I should add --- when I took my old thermostat, it had a large visible crack on one part of it. As I said, I had low coolant, so perhaps it overheated and cracked due to that. Or maybe it cracked first and then the overheating started.
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  #22  
Old 02-08-2013, 11:08 AM
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BMR_LVR BMR_LVR is offline
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Keep a close eye on the coolant level and engine temp. If all holds well for a week or so, you should be golden. But, keep in the back of your mind that you had a serious overheat, so your head and HG may still be more vulnerable.
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Most problems are usually something simple !

Quote:
Originally Posted by noego View Post
It's Deja Poo - as in, I've heard this **** before.
Steve

Calypso Red 1992 525i with 200K miles

1991 735i - Sold
1992 525i - Sold
1995 325is - Sold
2000 528i - Sold

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  #23  
Old 02-08-2013, 12:26 PM
///Brillantrot ///Brillantrot is offline
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Quote:
Originally Posted by samsonnyc View Post
Adaptations on our ecu comprise only 10% of the car's behaviour, and are only about optimising performance. The adaptations are not about maintaining normal behaviour. And optimisations are more for general drivability and gear shift points for automatics, and not for engine heat response.

So I must disagree with pretty much all that you've said here.

And the electric fan's has is activated by the radiator coolant sensor. The ecu is not involved.
I can't really totally disagree with your disagreement. I was just looking for the easiest thing possible for him to eliminate. I once ran my e34 m5 for a number of days with my air intake set up in such a way that the MAF was making significantly incorrect readings. After I fixed it, the car still absolutely refused to run correctly, idling horribly rough, stalling and acting totally unpredictable at high rpm. I reset the ecu under the same basic theory that I suggested in my last post and the problem was completely resolved, never to resurface again. It was the lowest lying fruit, so I picked it first and it happened to work, likely saving me considerable time and money. I believe that a "confused" (via receiving unnaturally altered information over a period of time) ecu can cause fairly dramatic/noticeable issues... that may be where we disagree.
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Old 02-08-2013, 12:40 PM
artemyk artemyk is offline
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That's good to know. So one can reset it just by disconnecting the battery?
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  #25  
Old 02-08-2013, 12:53 PM
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Monsignor Monsignor is offline
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Quote:
Originally Posted by ///Brillantrot View Post
I can't really totally disagree with your disagreement. I was just looking for the easiest thing possible for him to eliminate. I once ran my e34 m5 for a number of days with my air intake set up in such a way that the MAF was making significantly incorrect readings. After I fixed it, the car still absolutely refused to run correctly, idling horribly rough, stalling and acting totally unpredictable at high rpm. I reset the ecu under the same basic theory that I suggested in my last post and the problem was completely resolved, never to resurface again. It was the lowest lying fruit, so I picked it first and it happened to work, likely saving me considerable time and money. I believe that a "confused" (via receiving unnaturally altered information over a period of time) ecu can cause fairly dramatic/noticeable issues... that may be where we disagree.
Welcome to the fest. Pics of that M5 bro!! Not many members here (like none) have an M5. Good to see your lurking has still proven fruitful.

So tell me, which AFM to MAF conversion kit did you use on it?

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