engine overcooling

[karter16]

Now can a bad battery cause the needle to fluctuate?

No. The DME takes sensor supply voltage into account when measuring sensor values. If your supply voltage was off by too much the DME would throw a code.

[BL92]

What is INPA saying on yours?

I can confirm on mine at idle sits at 80c in INPA, Gauge off centre toward cold, and my thermo is running

[sapote]

No. The DME takes sensor supply voltage into account when measuring sensor values. If your supply voltage was off by too much the DME would throw a code.

The batt voltage varies a lot depending on engine running or not, and so all sensor output were designed with operating range much less than 12v, probably in the 5v domain because the DME processor ADC is a 5v peripheral. IOW, all sensor circuits are running at regulated 5v before feeding to the processor ADC inputs.

[karter16]

The batt voltage varies a lot depending on engine running or not, and so all sensor output were designed with operating range much less than 12v, probably in the 5v domain because the DME processor ADC is a 5v peripheral. IOW, all sensor circuits are running at regulated 5v before feeding to the processor ADC inputs.

Correct. The DME also monitors the exact supply voltage to the sensor and uses that as a reference when reading the ADCs. Eg if sensor supply voltage is 4.995V instead of 5.000V the DME will take that into account.


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[kimumu]

What is INPA saying on yours?

I can confirm on mine at idle sits at 80c in INPA, Gauge off centre toward cold, and my thermo is running

So this is what I got from inpa and the car was driven for about 30 minutes. Ambient temperature is 16 Celsius. The needle was pointing at slightly over 11 o'clock. I noticed after bleeding yesterday, the needle still fluctuates but feel it is getting better meaning it doesn't drop like before. Before when it drops it would almost get to the first dot. Now it doesn't get to that far.

[Barracooda]

That looks pretty normal to me, the stock thermostat is 80 degrees Celsius. You can monitor and watch the outlet temp rise and fall as the thermostat opens and the radiator does it's thing.

[sapote]

So this is what I got from inpa and the car was driven for about 30 minutes. Ambient temperature is 16 Celsius.

I suggested: Use INPA to monitor both the radiator outlet and engine coolant temperature sensors while driving, pay attention to when the radiator outlet temperature STARTS going up at what engine temperature.

In this case, the outlet started at 20C or lower so you should be able to catch the engine T when the outlet starts rising, and this tell when the Tstat opens.

I think 79C is on the low side. Mine is around 83 - 84C cruising.

[kimumu]

I suggested: Use INPA to monitor both the radiator outlet and engine coolant temperature sensors while driving, pay attention to when the radiator outlet temperature STARTS going up at what engine temperature.

In this case, the outlet started at 20C or lower so you should be able to catch the engine T when the outlet starts rising, and this tell when the Tstat opens.

I think 79C is on the low side. Mine is around 83 - 84C cruising.

I monitored both the radiator outlet temperature and engine coolant temperature using inpa. The radiator outlet temperature started rising when the engine coolant temperature reached 80 degrees and started dropping when the engine coolant temperature dropped below 80 degrees which means the thermostat is working fine.

The engine coolant temperature just won't pass 80 degrees when idle or if I drive normally. But when I kind of pushes it hard, it will reach 83, 84 degrees but drop down as soon as I take my foot off of the pedal.

What else can cause this if thermostat is working fine?

[BMWfanz]

I monitored both the radiator outlet temperature and engine coolant temperature using inpa. The radiator outlet temperature started rising when the engine coolant temperature reached 80 degrees and started dropping when the engine coolant temperature dropped below 80 degrees which means the thermostat is working fine.

The engine coolant temperature just won't pass 80 degrees when idle or if I drive normally. But when I kind of pushes it hard, it will reach 83, 84 degrees but drop down as soon as I take my foot off of the pedal.

What else can cause this if thermostat is working fine?

Its usual situation for S54, especially when the weather is not so hot. I've noticed that with good cooling system for properly oil temperature (90c for 10w60) is very tricky reachable when its not hot summer day.

[sapote]

What else can cause this if thermostat is working fine?

Your system is working normal with a 80C-Tstat. If you want to have hotter engine then try to find a hotter Tstat.

[kimumu]

Ok. so my car's problem kind of is solved. 2 things happening here.
First, I didn't bleed the coolant well enough. I left the coolant resovir cap off and started the engine. My amount bubble came out was astonishing. It kept burping air out for 5 straight minutes. And for months the first time I saw the needle stayed bang in the middle. Went for a drive for 10 minutes and no temperature rising nor dropping. I did this while the aux fan was unplugged.

Second, I think my aux fan is cooked. The moment I plugged it, the temperature started dropping to almost the first dot. Also, oil temperature was dropping. It was spinning all time even when the coolant outlet temperature dropped down. It kicked in at the coolant outlet temperature reached 55 degrees.
So I unplugged it again, and the temperature rose back to middle.

[BMWfanz]

Ok. so my car's problem kind of is solved. 2 things happening here.
First, I didn't bleed the coolant well enough. I left the coolant resovir cap off and started the engine. My amount bubble came out was astonishing. It kept burping air out for 5 straight minutes. And for months the first time I saw the needle stayed bang in the middle. Went for a drive for 10 minutes and no temperature rising nor dropping. I did this while the aux fan was unplugged.

Second, I think my aux fan is cooked. The moment I plugged it, the temperature started dropping to almost the first dot. Also, oil temperature was dropping. It was spinning all time even when the coolant outlet temperature dropped down. It kicked in at the coolant outlet temperature reached 55 degrees.
So I unplugged it again, and the temperature rose back to middle.

Aux fan is controlled by ECU, based on outlet radiator housing temperature.

[jayjaya29]

I would replace the outlet radiator temp sensor first. If the aux fan is still constantly on then you need a new aux fan assembly, the controller box on the fan itself can die and trigger the fan to run constantly.

[bigjae46]

Ok. so my car's problem kind of is solved. 2 things happening here.
First, I didn't bleed the coolant well enough. I left the coolant resovir cap off and started the engine. My amount bubble came out was astonishing. It kept burping air out for 5 straight minutes. And for months the first time I saw the needle stayed bang in the middle. Went for a drive for 10 minutes and no temperature rising nor dropping. I did this while the aux fan was unplugged.

Second, I think my aux fan is cooked. The moment I plugged it, the temperature started dropping to almost the first dot. Also, oil temperature was dropping. It was spinning all time even when the coolant outlet temperature dropped down. It kicked in at the coolant outlet temperature reached 55 degrees.
So I unplugged it again, and the temperature rose back to middle.

Interesting. Usually a bad bleed will cause higher temps. The S54 bleeds relatively easily but you still need to turn on the heater to open the heater core loop to get all of the air out. Otherwise it is as easy as pour in coolant and go. The M54 is a different story.

[kimumu]

I would replace the outlet radiator temp sensor first. If the aux fan is still constantly on then you need a new aux fan assembly, the controller box on the fan itself can die and trigger the fan to run constantly.

I have already replaced it 2 weeks ago. It's not running constantly, it runs too early.