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Old 11-29-2016, 06:23 PM   #1
paperpilot22
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325Ci Overheat at idle

Okay I'll present what's become a tricky issue for me. I'm sure you smart folks here can assist. I've looked through the boards here and it's really impressive to see the expertise here.

My coolant expansion tank blew the other day so I replaced it, the lower thermostat, and the water pump (it was noisy anyways). Everything went back together well and I bled the system a few times.

Since doing the repair I notice the temperature will do some strange things. I drive for about 20 minutes and then, when I sit at idle, the car begins to get hot.

The aux fan turns on when the AC is on but I don't see it otherwise. All fuses check good. The coolant level is good. All connections look good. The heater blows hot air (and brings the engine temp down). The AC blows cold.


Maybe the temperature sensor?

Thanks very much for any help you can give. I really appreciate it.


And of course, once I figure this I'll bring up the 0171/0174 issue. Man I can't tie that thing down. What a pain.
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Old 11-29-2016, 07:25 PM   #2
Loaded325i
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Why did you put a lower temp thermostat in? Sometimes when people do that sort of stuff the radiator never has time to cool the coolant mixture because the t-stat is always open instead of cycling open and close.
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Old 11-29-2016, 07:31 PM   #3
paperpilot22
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I'm probably using the incorrect name. It's the thermostat at the bottom of the expansion tank. It broke as I removed the tank so I had to replace it.
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Old 11-30-2016, 08:56 AM   #4
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Quote:
Originally Posted by paperpilot22 View Post
I'm probably using the incorrect name. It's the thermostat at the bottom of the expansion tank. It broke as I removed the tank so I had to replace it.

That's the thermostat for the automatic tranny fluid. Your car has 2 fans. The one in front of the radiator cools the AC condenser. The other is attached to the water pump via a thermally activated fluid clutch. That is, when under hood temps get high the clutch fluid will increase in viscosity thus speeding up the fan speed. That clutch is going bad.
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Old 11-30-2016, 09:58 AM   #5
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It sounds like your aux fan is not coming on when it should. Read this and check it.
https://drive.google.com/file/d/0B59...k5SkwxVlE/view
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Old 11-30-2016, 11:23 AM   #6
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I would check the fan clutch, as stated above it might be bad. Or the tstat or water pump, if none of these has been replaced recently, it may be time.
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Old 11-30-2016, 11:50 AM   #7
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BaliDawg is referring to the electric aux fan. Sounds like a classic failure via intermittent operation. Prudent to verify the CTS is functional though. Measure the ohm difference Hot vs Cold - should be > 200ohms Directions in the linked guide in BD's post.
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Old 12-04-2016, 05:18 PM   #8
paperpilot22
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I replaced the fan clutch and it seems to be doing very well. I had no idea how bad the old one sounded till I heard this new. it's just smoother.

But, of course, the same problem occurred. I went out driving for a while and the temp held, then the stop and go traffic took its toll and it got real hot, real quick. I have everything taken apart and don't see any obvious issue. I'm guessing perhaps the electric fan. In reading the document, which gives great information, I'm still not sure what part may be failing. The aux fan runs fine but must not be getting to full speed. What would that indicate? Otherwise, I've pretty much replaced everything else possible (I replaced the CTS a year ago).

Any thoughts?
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Old 12-04-2016, 07:22 PM   #9
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As Balidawg pointed out earlier, it is likely your electric fan and not the clutch fan that is the root of the overheating.

The electric fan module often fails on speed ratios and may work at certain times. The DME uses algebraic formulas with multiple inputs to calculate the output speed. This data is sent to the fan module as a PWM signal.

I think sometimes the fan module just doesn't put out the right power or misinterprets DME command signal. Often corrosion on terminals can cause this. You need to replace your electric fan assembly or minimally the Bosch fan module mounted on the shroud.

Last edited by BMW-North; 12-04-2016 at 07:25 PM. Reason: I typed PWM. Apple prefers Pam.
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Old 12-04-2016, 07:57 PM   #10
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I think you're absolutely correct. And I definitely appreciate the input. I'll check out the fan and see if it's a connection issue or the whole fan. Either way I'm anxious to get it settled.

Thanks very much!
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Old 12-09-2016, 07:11 PM   #11
paperpilot22
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Electric fan

I replaced the electric fan and it isn't coming on at all...even with the AC on at idle. It should come on then, correct?

Should I take it for a drive to fully warm it up or is it showing me that it's not working already?

Gotta be honest, I'm running to of ideas on this. One fix creates another problem it seems. Any input is very appreciated.
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Old 12-09-2016, 08:48 PM   #12
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I know you replaced the pump but it sounds like you don't have enough flow at idle. Either a restriction or bad pump. T-stat still good?
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Old 12-09-2016, 08:54 PM   #13
paperpilot22
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I think it's good. i replaced it about a year ago. I'm not sure about a restriction.

One thing I did notice, if it helps, is when it was getting real hot a few days ago, the hose from the thermostat to the expansion tank was very firm. I know it's got some pressure to it but I couldn't even squeeze it hardly.

Is that normal or could that show a restriction somewhere? Also, what about the fan never turning on? Is there a mistake I could have made installing it?
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Old 12-09-2016, 10:16 PM   #14
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Did you check the lower rad hose coolant temp sensor as stated earlier. If you disconnect it ( the cts) then start car, then turn on ac the fan should fire up. It maybe putting out false values which mess with DME output calc.
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Old 12-09-2016, 10:17 PM   #15
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Quote:
Originally Posted by paperpilot22 View Post
I think it's good. i replaced it about a year ago. I'm not sure about a restriction.

One thing I did notice, if it helps, is when it was getting real hot a few days ago, the hose from the thermostat to the expansion tank was very firm. I know it's got some pressure to it but I couldn't even squeeze it hardly.

Is that normal or could that show a restriction somewhere? Also, what about the fan never turning on? Is there a mistake I could have made installing it?
Reading this sounds like your tstat is closed shut or the water pump isn't working. Either way sounds like a coolant circulation issue.


Edit: if the coolant isn't circulating the the coolant at the CTS will not be hot enough to send a reading to DME that would command the fan be turned on. I think a thorough diagnosis of the cooling components is warranted.

Last edited by BMW-North; 12-09-2016 at 10:19 PM.
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Old 12-10-2016, 09:56 AM   #16
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I was going to suggest the t-stat, but I would think it would run hot under all conditions, like air in the system. A friends e34 had a bad stat and using the heater was the only way to keep it cool, that was on an m20.
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Old 12-10-2016, 10:52 AM   #17
paperpilot22
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It's a shame this all started from that stupid expansion tank cracking.

I tried disconnecting the CTS and having the ac on but the fan doesn't move. The only way to get the fan spinning is to unplug its connector and reconnect it. The fan will spin up to speed then wind down. I may have to admit defeat and take it to a pro for a good look over. I think all your advice is spot on. There must be something strange happening that I'm overlooking.
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Old 12-10-2016, 12:13 PM   #18
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The clutch fan should be enough to keep the car from overheating at idle, I think you have a flow problem.
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Old 12-10-2016, 12:20 PM   #19
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Inpa fan test or a known good fan module from another's car to test. See my video on YouTube testing a different fan Assy without uninstalling the old one on an automatic.
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Old 12-11-2016, 11:05 PM   #20
paperpilot22
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Changed out the thermostat and it seems to have done the trick. I drove the car all over for an hour and the temp is rock solid. I appreciate the inputs. You were all correct, as usual. I'm still unsure why the aux fan never turns on, but for now the car can drive so I'm glad.

Now on to the 171 and 174 codes....haha
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