Erratic engine temps

[topaz540i]

All temps observed thru test 7 data-


Car had been running cool all summer (94-96C) considering i have no mech fan.

Installed new thermo, temps return to normal 104-106C for about a week. Now im running cold again.
Today car would not go over 96C and at one point i watched it dive down to 88 and back up in a matter of a few seconds.


I take the car out again and its running even cooler now at about 88. At a stop sign i do a 0-100 run and the temp finally breaks the barrier and reaches 102 while accelerating full throttle and then eventually reaches the full 106 on the ride home but only after the high speed run.


Had i been running the correct temp the whole time and the higher rpms (higher water pump speed) simply flushed a dirty sensor? My hand scanner seems to back up test 7 data but where do they get the feed? The thermo or elsewhere?


The car always seems to take forever to warm up even when its running right. Im usually in it for a few miles before its up to temp which i assume is normal although way slower than any other vehicle i have ever had. I know this because i wait for it to warm up before bothering to turn the heat on and/or driving hard, which sucks to wait so long for.


Btw i have a 0443 evap purge code which i believe is unrelated. That is more of a cold start warm the cats up quickly device not engine control.

[Flug540]

The cluster reads its temp from the dual temp sensor located at the front of the engine on top of the water pump. One of the two sensors goes to the DME, the other to the cluster.

Your "erratic" readings might be normal, it doesn't make sense to me either, but when I started monitoring my temp, I saw something similar. My temps were generally higher though probably because of the S/C + Evans combination. Sometimes they would go and stay 108-110, but sometimes dive to 100.

I'm currently experimenting with basically a multi-channel PWM that directly controls the t-stat and the electric fan. Both have separately pre-set temp ranges and since I've done the mod, the temp is much more stable and very predictable.

[edjack]

You can get a cheapo IR thermometer at Harbor Freight, and compare the readings. I would suspect the sensor.

[topaz540i]

On realoem i see one temp sensor in the water pump and another in a lower radiator hose. What does the one in the hose do?

http://realoem.com/bmw/showparts.do?...67&hg=11&fg=35
Part#12

[Flug540]

On realoem i see one temp sensor in the water pump and another in a lower radiator hose. What does the one in the hose do?

http://realoem.com/bmw/showparts.do?...67&hg=11&fg=35
Part#12

Not sure, maybe Aux fan.

[rdl]

On realoem i see one temp sensor in the water pump and another in a lower radiator hose. What does the one in the hose do?
...

The sensor in the lower rad hose is used to control the auxillary fan in front of the radiator/AC condenser. There were 2 modes of control depending on model year. In earlier designs the sensor is a multi-pole temperature switch which turns relays on/off in stages for 3 possible fan speeds. For the later design the sensor is a thermistor providing a temperature signal to the DME which then controls the aux fan in 20+ speed using a PWM signal to the fan control module - no relays.

The notion in both designs is that the aux fan runs only when the radiator isn't able to provide "cool" flow to the engine; "cool" being approximately 80C. This results in a seemingly strange result that the engine could be overheating while the aux fan is not running. E.g. the thermostat fails to open, the engine overheats, the radiator outlet though is quite cool/cold because little or no hot coolant is released into the radiator, auxillary fan is still.

In both designs, A/C operation is also able to turn on the aux fan indpendently of the rad outlet temperature.

In total then it's an either/or for the auxillary fan to be turned on.
EDIT: more precisely I should have said either - or - or both.

Regards
RDL

[auaq]

I'm not much familiar with the V8 powered E39 and their cooling system controls. Since the temperatures are dropping to freezing temps nowadays it may be possible that it takes a quite a while for the engine to reach operating temperatures. Also, I have observed my readings that fluctuate up and down a little bit but I personally don't think that it is a problem. So, I don't it is a concern thing, yet again I am not too familiar with M62's cooling system.

[YotaMike]

Did you notice any increase in mpg when your temps were in the 104-106 range as opposed to 94-96?