@jet; That is exactly the problem with modern workshop; as long as the 'computer' doesn't generate a fault code they are reluctant to admit there is something wrong with the car. Diagnosing a problem without the use of a computer is a skill that is disappearing slowly. Sad but true.

 

Here are my final stats with old and new thermostat. Same route nearly same time of day. Avg speed was lower suggesting more traffic or perhaps I feathered the throttle a bit more.




Old therm new % improvement
Ambient 9? 13.5?
engine starting 25? 14?

Time to warm ?
10 mins 52 65 25.00%
13 mins 60 76
18 mins 70 84
21 mins 75 80
30 mins 78 90

mpg 28.1 32.1 14.23%
ltrs /100km 10.05 8.8
avg mph 37.8 30.8

N.B mine is a pre line change 530d auto with extras that push weight up.

I notice the particulate filter is making the droning noise on a constant throttle now and the last owner has it cleaned at service (only 38k) so perhaps this is a warning you are running cool your particulate will clog up.

The dealers: Stratstone in Maidenhead '000s spent there and while I cannot prove the thermostat problem existed then I think it probably did, Birds of Iver near Slough number one on my list of problems was poor mpg, very polite but no message on the computer so no solution, they also charged me ?100 to tell me they could not do the software upgrade they said was possible when I booked in. Lastly Sytner of Ascot who very kindly did a software upgrade to solve a multitude of problems but did not link poor economy to the thermostat.

 

what's your opinion on my situation, poor mpg, about 22mpg, replaced egr thermo, car get to 87 degrees at most, but can get to 90+ degrees(Some times 95 Degrees) when stationary, but goes rapidly back down to 87 degrees as the car moves of again.

do you think i should get my main thermo changed for the sake of 3-4 degrees, would any of you guys get it done?

 

In my opinion you have no hurry to replace the main thermostat. If you have diesel then the DPF will start its cleaning cycle when prequisites are met, and one of them is temp 80C. So you have 7 degrees to spare..

 

how can you tell when it goes into dpf????

 

Someone said on the forum it makes a dronning noise, like a faint whirring from the back of the car in my case. At first I thought it was the rear air suspension on my estate levelling.

You probably have enough temperture. Part of it is how long does it take to reach 87, I'd say if it takes much longer than 30 mins to get to 87 you could be suffering on mpg. If you want to warm up quicker turn down the tmperature on both climate control knobs, I noticed that makes a difference.

To get 22mpg you must be in short journeys in town. Try warming the car up reset the mpg readout and on a gentle run see if you get a more representative figure like 34+.

My journey to improve mpg has included - changing driving style, reseting gearbox software, replacing runflats (yeah someone said that would help), upgrading all software versions and now the thermostat. I'll do a few tankfuls to get the final results but I'd guess I have gone from 25ish to 29ish mpg in mainly suburban driving. I had an old CIP version, the new gearbox software (changes up earlier and less loss slurring), maybe the engine management upgrade (vibration gone) upgrade and the thermostat made the most difference.

These cars are so different and errr more challenging than my old 330i.

 

It's not only a question about 3-4 degrees when warm, as that is probably negligable. But the variation in temperature depending on whether you're standing still or moving indicates that the thermostat doesn't close properly. Therefore water gets past the thermostat to the radiator all the time, cooling the engine even when it tries to warm up. This leads to longer warm-up time and is probably not good for either engine or fuel consumption.

I would change it.

 

Aint that the truth, I miss my 330i now. It never asked for anything compare to this spoilt brat, too likeable to get rid of though.

 

HI ALL

just had my car into dealers with reference to the main thermo problem. I have had it changed (done as foreign car, cost ?100, with part) and on the way back from the dealer which is about 8 mile from home, the cars temperature was between 90-91 degrees, and stayed constant throughout

The mpg has shot up from 22mpg to 26.2mpg.

So all you ppl with low mpg, more than likely it is due to low operating temperatures. In my case my car was getting to about 87 degrees and getting faulty part changed has given me an extra 4+ mpg, and that's because the car was operating 4 degrees less than normal.

The tech at the dealer was a little unsure to why i was getting the main thermo changed, and said that i would be better of getting the whole ECU reprogrammed, but he didn't have enough time to do that as their Laptop was on some other cars. He said he will sort that out for me for about ?80.00, sometime next week. He says i will get mpg just like in the handbook.

 

glad your mpg has improved! Good deal on replacement too.