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Old 11-04-2012, 04:16 PM
Pierre Louis Pierre Louis is offline
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Location: US
Join Date: Oct 2011
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Mein Auto: BMW
Originally Posted by Penguin View Post
Most temperature gauges form the vehicle manufacturers nowadays little are more than a fancy idiot light. They now are run by the computer and "normalized." This means they basically have three readings (1) cold, (2) "normal" and (3) Overheating. The computer monitors the temperature and as soon as the engine reaches a predetermined temperature threshold it quickly bring the gauge needle to the vertical "normal" position. As long as the temperature in is the "normal" range, the computer keeps it vertical. If the engine exceeds a predetermined high temperature, the computer quickly moves the needle to the "hot" position. This limits the usefulness of a temperature gauge, because as long as the temperature is in the "normal" range, the needle does not move.

Why did they do this? Because many people nowadays have more money (or credit) than brains. The manufacturers got tired of complaints from people when the temperature needle went to the top of the "normal" range when they were driving in stop and go city traffic, with the A/C full blast, and an outside temperature of 110 degrees. "What do you mean that's normal? I spend $70,000 for this vehicle and it shouldn't run hot, don't give me that BS, now fix it!"

So BMW, and others, went to normalizing the gauge to get rid of such unfounded complaints by people who don't understand engine cooling.
Although this sounds plausible, my 2005 E320 CDI did not have such a setup. The temperature guage did read differently in differing conditions. In fact, a common problem of that year was a "stuck open" thermostat where the temperature was unusually low most of the time and so was mine. I also suffered a failure of the coolant control valve where I lost heat during the winter, so the coolant temperature guage was useful then too. Finally, when my electric radiator fan control circuit failed and my engine began to overheat, it was very useful knowing how long to drive it and under what conditions until I could get the thing fixed ($$$) without cooking the engine. It was a very useful guage and Mercedes did well to make it so.

As far as the aluminum block BMW diesels, this may not be the same situation. I would not risk ANY overheating with such an engine, given the chance of warping the block/head. Mercedes still uses cast iron/other alloys for its diesel engines or so I hear.


Last edited by Pierre Louis; 11-04-2012 at 04:19 PM.
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