E39 behaving strangely in tailback
Discussion
Drove from Devon to Herts today after a short break; car is a '00/W 528se auto.
Unfortunately there was a nasty looking accident on the M5. I'm not complaining about the tailback, because the occupants of the cars involved clearly had a much worse day than I did.
We spent at least an hour either stationary or crawling.
I happened to have the OBC displaying outside temperature.
After about 30mins in the jam the display started climbing - reaching 36.5c, before we got moving again and it came back down.
At the same time the climate control (set at 20deg - similar to the real outside temp) started pumping out chilled air.
The coolant temp gauge was rock-steady at half-way, as usual.
Stopped at the next services for half an hour; no signs of anything untoward under the bonnet.
The rest of the journey was mostly at normal cruising speed, though there was another incident - and the same symptoms started to occur. However, the delay was shorter and we were soon back to normal.
What was going on? Any theories?
Unfortunately there was a nasty looking accident on the M5. I'm not complaining about the tailback, because the occupants of the cars involved clearly had a much worse day than I did.
We spent at least an hour either stationary or crawling.
I happened to have the OBC displaying outside temperature.
After about 30mins in the jam the display started climbing - reaching 36.5c, before we got moving again and it came back down.
At the same time the climate control (set at 20deg - similar to the real outside temp) started pumping out chilled air.
The coolant temp gauge was rock-steady at half-way, as usual.
Stopped at the next services for half an hour; no signs of anything untoward under the bonnet.
The rest of the journey was mostly at normal cruising speed, though there was another incident - and the same symptoms started to occur. However, the delay was shorter and we were soon back to normal.
What was going on? Any theories?
The air temp sensor in in a brake duct usually, when sitting for a while, it starts to pick up the hot air from the engine rather than the colder ambient air.
The climate control might have picked up the cabin temp to be creeping over 20'C, and start the aircon on cold to bring the temps down.
The climate control might have picked up the cabin temp to be creeping over 20'C, and start the aircon on cold to bring the temps down.
TheEnd said:
The air temp sensor in in a brake duct usually, when sitting for a while, it starts to pick up the hot air from the engine rather than the colder ambient air.
The climate control might have picked up the cabin temp to be creeping over 20'C, and start the aircon on cold to bring the temps down.
Yes, thanks. Your first point makes sense; I was thinking along those lines - but didn't know where the sensor was.The climate control might have picked up the cabin temp to be creeping over 20'C, and start the aircon on cold to bring the temps down.
The aircon just seemed a little over enthusiastic (I was trying to keep an elderly passenger comfortable),
probably my imagination.
The sensor isn't in a brake duct, it's underneath the front offside corner of the bumper. There is nothing but air between it (though it sits in a recess) and the road. It is outside of the engine bay.
Mine has never fluctuated in this way and has only ever given me a questionable reading once - when it was sheered off at 70mph by some perspex in the outside lane of the Motorway - so I'd suggest something is wrong here.
Mine has never fluctuated in this way and has only ever given me a questionable reading once - when it was sheered off at 70mph by some perspex in the outside lane of the Motorway - so I'd suggest something is wrong here.
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