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Old 05-29-2003, 04:38 PM
Registered User
Join Date: May 2003
Location: Phoenix
Posts: 4
Question Slow response of S500 ambient temp reading

It's getting pretty hot in Phoenix now, 111F yesterday. When I start up my '94 S500s in the morining, the temp reading in the car registers ambient temp of garage around 80s and then freezes to response regardless the outside being at 90s or 100s. It will have to wait for a 5 miles local drive until the freeway or 30 minutes local drive and then the temperature reading suddenly jumps to correct reading in few seconds. At the mean time, A/C starts to pump much colder air into the vent. I wonder if this is normal or not? Both of my S500 and S500C have the same problem. Can someone kindly let me know?
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Old 05-29-2003, 05:41 PM
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
It could easily be proper. The temp sensor indication is mapped. It reads the last reading usually after a restart and has some degree of delays.

One of the main purposes is to avoid reading the radiator temp on a car that has only been off for a small period. The sensor is in the bumper and is heated by the radiator untill moving.
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
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Old 05-29-2003, 07:13 PM
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Join Date: Jun 2001
Location: Omaha, NE
Posts: 962
In addition to what Steve said, the system is programmed to not change to a higher temp very quickly when your speed is low, to avoid erroneously high reading when in stop-and-go driving. It will update faster when your speed picks up.

However, for safety reasons it will always update to a LOWER temperature if the ambient temp drops. This is to alert you to potential icy road conditions.

Pretty clever, huh?
'93 400E
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Old 05-29-2003, 08:07 PM
Registered User
Join Date: May 2003
Location: Phoenix
Posts: 4
What a clever design by MB of S500! The sensor will go only one-way quickly, down. Is this feature installed on other MB car also? SLK's temp seems to respond immediately when engine was just started! Or, it is just W140 car having this protection.
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Old 05-29-2003, 08:08 PM
Registered User
Join Date: Mar 2003
Location: Chandler Arizona
Posts: 20
My 1994 C-280 (a phoenix car) has done the same thing since I bought the car new in 1994. I guess this is normal. My outside temp gauge reads 4 degrees high and has since new. I'm assuming there isn't any way to adjust it, it there?
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