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  #1  
Old 05-15-2019, 10:38 PM
germans germans is offline
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Mein Auto:
Replacing sensors after water heater fail overheat

I purchased this used 07 328i BMW e90 recently and the previous owner had a water pump failure and replaced the water pump and possibly the thermostat.

I've been working through some issues that believe were a direct result from the overheating, failed sensors. The coolant would rise above the normal level and the other issue is that fan would sometimes come on high and would sort of get stuck and not shut off when turning off AC.

I replaced the coolant level sensor which fixed the one issue and today replaced the coolant temperature sensor that screws into the oil filter housing. Now the fan does not run as high and slows up when turning off the AC.

I'm now thinking of possibly replacing BMW Auxiliary Fan Switch - OEM Supplier 13621433077 with a new one. I'm just wondering if this part gets damaged like the other two or if it is pretty safe. I read somewhere in Pelican Parts forum that some guy said these rarely ever fail. Since the fan already seems to be working properly, I'm just wondering if it is necessary. Any thoughts?
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Old 05-16-2019, 11:42 AM
gbalthrop gbalthrop is offline
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Mein Auto: 2007 328xi E91
[QUOTE=germans;13002021]...07 328i BMW e90...previous owner had a water pump failure and replaced the water pump and possibly the thermostat. I've been working through some issues that believe were a direct result from the overheating, failed sensors. [1] The coolant would rise above the normal level and the other issue is that fan would sometimes come on high and would sort of get stuck and not shut off when turning off AC.

I replaced the coolant level sensor which fixed the one issue and [2] today replaced the coolant temperature sensor that screws into the oil filter housing. Now the fan does not run as high and slows up when turning off the AC.

[3] I'm now thinking of possibly replacing BMW Auxiliary Fan Switch - OEM Supplier 13621433077 with a new one. I'm just wondering if this part gets damaged like the other two or if it is pretty safe. [COLOR="Red"]I read somewhere in Pelican Parts forum that some guy said these rarely ever fail[COLOR]...
[QUOTE]

[3] You can't believe everything you read on the Web. THAT statement is probably RIGHT for the WRONG reason: AFAIK N52K engined vehicles sold in the US do NOT have that sensor. You don't say where you are located, but WHEREVER you are, you should locate that sensor on the Lower Radiator Hose to see that you have one BEFORE thinking about replacing it.

My 2007 328xi E91 N52K built 3/14/2007 does NOT have such a sensor in the lower radiator hose, and I have NOT heard of anyone in the US with a 328i/xi built after 3/1/2007 who HAS ONE. Here is the Autohaus page for that part. NOTE the caution related to "variations" -- "Factory variations exist, please verify existing unit prior to ordering":
https://www.autohausaz.com/pn/13621433077

My concepts of the other two "Sensors" you discuss differ from those you describe:

1) First, the Coolant Reservoir Level "Sensor" is actually a simple ON/OFF SWITCH and NOT a sensor. If you refer to the TIS circuit diagram for that component (S63b), you will see that it simply completes a Ground signal to the JBE (Junction Box Electronic Module) when the Coolant Level falls too low in the Reservoir, causing the warning light to be lit on the Instrument Cluster to which the JBE is connected. The Handbrake Warning Switch and Washer Fluid Level Switch shown next to the Coolant Level Switch work similarly. Here are the TIS circuit & Installation Location:
https://www.newtis.info/tisv2/a/en/e...lights/pqQfddR
https://www.newtis.info/tisv2/a/en/e...switch/RRuQGq8

Seeing HOW that Switch (That's why its ID# begins with "S" for Switch instead of "B" used for Sensors) functions and where it is located, I can't see any way that "Overheating" (if it ACTUALLY occurred -- see below) would affect its function. ALSO, I can't see any way that switch would AFFECT coolant level. It does NOT regulate or control coolant level in any way, it's just a dumb switch causing a warning light to come on if reservoir level drops below a certain point.

2) The ECTS (Engine Coolant Temperature Sensor) IS a sensor as you see from the next TIS circuit diagram, and its ID# in the schematic is "B6236a". It sends a signal to the DME to which it is directly attached. That signal is a Voltage which varies with coolant temperature in the Housing where it is mounted. The DME uses that ECTS temperature signal for everything from regulating fueling enrichment (choke) when engine is cold to setting waterpump speed and radiator fan speed (along with OTHER inputs to the DME).
https://www.newtis.info/tisv2/a/en/e...ooling/lqgyKuz

My concept is that it is at least as likely that the ECTS or its circuit was faulty BEFORE the water pump was replaced, and possibly was causing FALSE temperature signal to the DME (and the Instrument Cluster Overheat warning light) when the ACTUAL coolant temperature was LESS than that indicated by the ECTS signal. We'll never know as the actual ECTS Housing temp was NOT measured by an Infrared Thermometer. From your reported effect on radiator fan operation, it would appear that the ECTS WAS faulty in some way and that replacement was warranted. When it became faulty and what caused it is NOT clear.

Suffice it to say, that if coolant was NOT lost from the system when/IF it overheated, then temperature of the coolant to which the sensor was subjected did NOT exceed the boiling point of the coolant at system pressure (~ 250F) and that event should NOT have caused any damage to the ECTS.

If you see any flaw in any of the CONCEPTS described above, please advise, as my intent is to share and improve concepts of how these cars actually work, including my own concepts.

George
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Old 05-16-2019, 12:45 PM
germans germans is offline
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Mein Auto:
Thanks for the detailed information. The car is an N51 with General Motors transmission, not an N52.

My use of the word "sensor" is based on what I see on the websites that sell such things. "Coolant level sensor" is one such word advertised on websites such as FCP euro and all sites that sell the part. I don't know the exact inner workings of the part, I just am trying to make it clear the specific part I'm referring to.

I never thought about the switch or sensor being defective prior to the pump failing but that is interesting.

That dumb "coolant level sensor" that you were referring to not doing anything other than triggering a warning light did exactly that. However, after checking the level later on the ball was floating way above the max line. I noticed this after taking to the BMW dealer to have the recalls fixed then coming home, letting the engine cool, then checking the coolant level. I thought some dummy there had topped it off above the max level. At least three different times I noticed different coolant levels where the level had surpassed the initial maximum level that I had put in. I even used a turkey baster to lower it at one point.

All I have done during this time or since was to mark some small white marks on radiator cap and reservoir using touch up paint so that arrows can be clearly seen when closing lid. I previously wasn't closing it quite so tightly. So, this and the level sensor and now the coolant level has been staying exactly at the maximum level.

The coolant sensor switch that I replaced was actually the wrong one from what I intended. I was planning on replacing the lower one which is located below the secondary air pump assembly near the front of the engine. I ordered the part then realized it is not the lower one but is the upper one located to the oil filter housing, one that has the crush washer and threads, not the plastic one with clips on side and big thick o-ring.

Regardless, the fan previously was more like an AC fan switch jumping from one set speed to another going from next to nothing to super loud, high speed. Then it would sometimes get stuck in high speed mode after turning off AC, then had to shut off car to resolve it then restart. Now, under usual driving it seems to max out around 70% of this level when AC on, then drops down after turned off, seems more like a variable speed fan now from what I noticed in the parking lot when tested it.

Now, it seems a bit scary because it doesn't seem to run the fan that much. The part is like $15-20 for OEM and even if I take the old one out to test it, maybe the O-ring is shot, just not worth the trouble without having new parts there anyways so thinking of replacing it now just hoping the plastic clip doesn't break.

The other temperature sensor I replaced didn't throw an error code and readings on the secret BMW menu for coolant temp looked normal so no easy way to check these things from the menus from what I can tell. My ODB2 scanner doesn't show lots of stuff. Replacing it probably won't hurt, 95,000 miles on it, worse case its a waste of $15 or clip breaks.
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