Obc thermometer

[viz007]

I find the thermometer on my OBC seems to display the temp much higher than it really is, it seems to do it more on really hot days often showing a temp over 40°C! Any ideas?

[Brianmoooore]

Is the sensor mounted where it should be? The one on my E39 isn't, and that allows it to pick up the road temp. and heat from vehicles in front. I saw 46 degrees on it in France two years ago.
If the OBC is reading high, then the resistance of the sensor is somewhat less than it should be at any given temp. Is it a genuine sensor? Aftermarket stuff isn't always made to the same tolerences as that made for BMW.
The sensor is of the same type of construction as the infamous 'blue' engine temp. sensor, and can fail in the same way, although normally I would expect them to fail to a higher resistance, giving a falsely low temp. reading, rather than higher.

[viz007]

Thanks Brian. I've found on the wiki where the sensor is meant to be so I'll take a look and check if of is the original

[Speedtouch]

What model of E39 have you got, Brian? I've currently got a 1997 E39 523i, an apparently rare non-sunroof, manual gearbox version. Still runs good with coming up for 160,000 miles.

[Brianmoooore]

528i Touring auto, dating from the first year of this century. Not a low mileage one like yours though 298,000 at the moment and all running fine, 200,000+ miles of it on LPG.
Bought six years ago for peanuts, complete with the longest MOT fail certificate (2.5 sides of A4) I've ever seen

[Speedtouch]

Sounds like a trusty steed indeed. I rescued mine from a scrappy next to the bodyshop I work at, for £150 - the staff there couldn't work out how to get it started (the previous owner had driven it to the yard, parked it up and left the key under the windscreen wiper without telling them!)

A few bits and pieces later and it's a pretty good car for an outlay of around £200.