adam1

Just got back from test run and the following results apply

The car took 10-15 mins to get up 90 C and went up to 97. This was stop-start and stationary at times(10mins).
On a 5 mile 30 mph run it dropped to below 90 for a few mins and then went back up to 90.

However after leaving for 1hr and re-start it took 10 mins to get up to 80C.

The car does reduce temp when moving and drops below 90 at some points but does climb back up...it however goes beyond 90 when stationary.

Not sure if both thermos are working but get 20-25mpg stop-start driving.
It seems to get louder when hotter and can hear more diesel clatter as it warms up. The auto hung onto high gear for longer for an instant which made me worry a little.

Not sure whats causing low mpg ...getting above 90c is possible for my car.

Adam

mini_me

IF it can go above 90 I think you are ok.

The MPG on these big diesels varies a lot with driving style (highway vs city).

adam1

It takes a good 15-20 mins to get there but keeps dropping below 90 and i was wondering if the thermo opens to cool engine. I should be getting constant 90 as you state
earlier.

I will test at highway maybe tomorrow to see if it stays 90 constant when already at op temp.
The funny thing is when hot or after driving slow traffic for a while it does (engine and revs) sound louder than normal..and whistles too.....its not DPF cleaning is it.....

Not sure if i should change thermo or not i seem to be getting about 350 miles /tank for 58 L. Thats over 10l/100km.

Adam

trevorken

You still didn't mention which engine you have. Is it a 520d or a 535d?
For a 520d, it certainly is quite a lot.

adam1

Its 525d auto BMW fiqures 27 city, 36 combined and 45 highway.
My driving tends to be mainly city/short dist but would expect around 400-450/tank at least. However trip always is around 20-22mpg.

Robbage

Ok i have not done a full tank, but the most 'constant' measuring test is mway/ 70mph type with cruise control engaged. I used to get, if lucky 40-41mpg, like this. Today I got 44-45 no problems at all.

So it looks like 10% increase. FWIW if i went heavy town driving it would have plummeted to 20-25mpg previously so if 10% is consistent, i would expect another 2mpg in that config. I suspect in town driving the temp would often have been close to 90C due to lack of cooling air flowing, hence there would be less than 10% improvement.

Anyway my temps remain 89 ABSOLUTE min, and 90-92 usually cruising in 6th gea. Btw it is a manual 525d with a/c off. Without the wish to sound patronising, also check tyre pressures are exactly book values, and jack up esp the rear wheels and check the handbrake is not binding even very slightly....

adam1

Did a 15 mile highway test. The temps took 10-15mins to reach to 80c on city roads prior to approach to highway. and eventually reached 90 C on joinin highway.
However when I joined highway going 60-70mph the temps dropped to below 90 and were more like 75c it then got hotter but did not reach 90 but on coming off highway/motorway and joining slow traffic it reached above 90c even 97c

Does the fact that the temps drop below 90 mean anything..or is it just cos air cools down engine temp and no probs with Thermos EGR/ and main.

The trip OBC gave good results, i zeroed while driving and it average 45mpg which is similar to BMW figs.
Not sure how accurate that is but on return combined was about 33.
I normally only get 20-25mpg slow traffic even when temps 90c.

It seems my car can get to 90C in slow traffic but temp reduces to below 90(75-80) at high speeds but OBC mpg stays normal for car.

Not sure if i have an issue here but once warmed it does sound more harsher than cold.

Adam

Robbage

Hi Adam. Once your car has reached 90 it should never drop below 88 (main thermostat should close to stop water entering rad). My car behaved identically to yours and yes it would and still will reach 97 in very slow or still air prior to the cooling fan cutting in.

My car reaches 90c in 10 mins now. I suggest you change main and egr thermostats which will cost around ?50 + coolant + maybe labour as well. You might get even better mpg althoughyours sounds good anyway.

mini_me

Adam, you symptoms to me sound like there is still some coolant going through the radiator when it shouldn't.
Start off with the EGR therm. as it is an easy and cheap fix. If the temp doesn;t improve after that than you will have spent about EUR 30 and you have then rules out the EGR therm. which means that it most likely cause is the main thermostat.

Good luck.

Robbage

As Mini me says (to whom were very grateful he enlightened all of us to this) the egr is the first easy step. However idont think anybody in the 16 odd pages of this fully solved the prob without changing both therms. Maybe youll get lucky though. Let us know!