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BMW E39 5 Series 1997-2003 (525i, 528i, 540i, M5, sport wagon) Temperature gauge reading


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Last Post: Feb 24, 2008 3:01 PM Last Post By: robin.pain
robin.pain

Posts: 13
Registered: 12/09/03
Temperature gauge reading
Posted: Jan 24, 2008 7:52 AM
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Hi,
Has anyone experienced this and found a solution?
I have a 1998 535i. When the engine is warming up from cold with the temperature gauge showing approx 1/3 of the way up from cold, the needle suddenly jumps off the scale to the right.
After a few more minutes warm up, the needle goes back roughly to the position it was before reading incorrectly. The needle then continues to work towards the centre of the gauge and stays there once the car is fully up to temperature.
When this failure happens the DME registers a Coolant Temperature Sensor fault. I changed the sensor, but no change. The fault also seems to appear only during cold weather, it went away completely last summer and is now back again this winter.
I have monitored the reading from the C.T.S. in the Instrument Cluster test function and it fails at around 60 degrees C. When the failure occurs it reads -128C (a factor of 2 or 16). The reading then returns to 60 something degrees when it starts working again.
I have monitored the voltage across the C.T.S. and it doesn't see any jumps in the voltage when it fails, similarly the resistance of the C.T.S. changes smoothly on the warm up. Therefore, it seems that the DME is putting out the correct voltage and the wiring to the sensor from the DME is OK.
I am starting to suspect that the DME may be sending garbage information along the CAN bus to the Instrument Cluster.
Can anyone confirm this as a known fault? My local BMW dealer has not heard of it.
janusz

Posts: 20
Registered: 12/09/03
Temperature gauge reading
Posted: Jan 24, 2008 9:54 AM   in response to: robin.pain in response to: robin.pain
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You have air. Put heater on let car warm up and park it at an extreme angle with front of car pointing up. Get on the gas a little to get the coolant circulating (thermo must be open) This will rid of the problem as well as any sporradic overheating. If you ask me its a design flaw. You can also bleed the thermo. housing as well as radiator (bleeder screws) Let all know how it worked out.
janusz

Posts: 20
Registered: 12/09/03
Temperature gauge reading
Posted: Jan 24, 2008 9:56 AM   in response to: janusz in response to: janusz
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I should stress the key here is an extreme angle, I usually use front car ramps on a moderate natural incline
David e39

Posts: 102
Registered: 04/13/05
Re: Temperature gauge reading
Posted: Jan 24, 2008 12:15 PM   in response to: janusz in response to: janusz
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I don't think its air: the temp would not read -128.

Is the check engine light error you're getting P0116 (or P0114 - can't remember)? If so, it is not the temperature switch, it is actually the thermostat that is faulty. (This is true for the 540 -I'm assuming the 535 is similar)

The V8 has a strange thermostat - it has an integral electric heater in the thermostat that the onboard computer uses for fine temp control. If this heater is faulty, the onboard computer calls it an error and sets the engine temp to -128 and puts the guage to offscale hot. Strange but true.

The mechanical action of the thermostat is still working to keep engine temp control, so you should be fine to drive the car... but don't delay thermostat replcement too long.
robin.pain

Posts: 13
Registered: 12/09/03
Re: Temperature gauge reading
Posted: Jan 24, 2008 4:04 PM   in response to: David e39 in response to: David e39
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My fault code reader is a Peake Research one, so I just get a two digit hex code - can't remember what the code was off hand. I know it was the coolant temp sensor though.
I didn't realise that the DME monitored the thermostat heater as well as driving it. It makes sense what you say about the DME seeing it as an error and defaulting the temp to -128. Perhaps the heater is going open circuit intermittently.
I will try changing the thermostat & let you know what happens.
Thanks for the replies
Robin
Hasso

Posts: 502
Registered: 12/09/03
Re: Temperature gauge reading
Posted: Jan 25, 2008 1:34 AM   in response to: robin.pain in response to: robin.pain
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I would say they same as DavidE39, its a commen faulty on V8 540/535,I think the BMWoriginal faultycode is 139 (or169)=caracteristictermostat/sensor faulty or to low coolant level in the enginge becuse of airlock, that termostate dont open without contact with water normally. But this is also an electric termostat that the DME modul can open. Check also the cables so its not damaged or have bad connection
robin.pain

Posts: 13
Registered: 12/09/03
Re: Temperature gauge reading
Posted: Feb 24, 2008 3:01 PM   in response to: Hasso in response to: Hasso
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Hi all,

Just a quick update.
I have now chnaged the thermostat and the fault has not appeared since. The engine also seems to be reaching normal operating temperature more quickly.
So fingers crossed it will stay that way.

Robin

P.S. has anybody discovered what engine temperature is required to send the buffered gauge needle above the centre mark? While monitoring my car after the thermostat change the needle first hits centre at 75 degrees C and stays there right up to the normal operating temperature of 110 degrees.

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