I have similar results as above with all thermostats changed. MPG will get better, not much but still noticeably.
The engine runs smoother and as it runs hotter the exhaust gasses will be hotter-->DPF will stay cleaner and its burning cycle will work better. Thats at least what I think and hope.

Cold BWM diesel + autotranny + city driving= really bad MPG... I have auxiliary heater which runs also when driving if temps too low , that makes additional +1l/100km to fuel usage.

But at least the cabin temp rose up very fast even with outside temp of -27C ..
Tranny was bit sluggish then tho..

 

part number BM11.51.7.805.811 @ ?27.74 + VAT, been quoted ?329.08 supplied and fitted from dealer, (no warranty, expired)



i have located the correct part now and they stock it on the shelf, going to ask my mate at BMW sort it for me (does most of my work after hours, only charges a fraction of the labour)

PS@E61530DAT can you get us a write up on how to DIY on the main thermo pls

 

sorry guys its part number 4 on diagram, but i think you should be replacing 6 and 7 too.

 

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Here is the EGR diagram. Part number I think 11717787870. Shown as number 8.

I've been quoted ?140 and 2 weeks by a specialist for the main therm. A matter of wondering parmblagan where is you mate based not near Berks is he?

 

sorry but my mates at birmingham bmw

another chap has quoted ?50 labour, at BMW specialist, he reckons that if my car gets to 87 degrees, it should really make much difference to MPG if the correct operating temps are 91 degrees

i have ordered a service and repair manual for the e60, so soon as get that from ebay, i will post on how to change the main thermo, might even try it my self,

do you think that 3-4 degrees difference will make a great deal of difference to MPG?

 

How quickly does it reach 87c?

Since both my thermostats have been changed my car reaches 91c between 5-10 miles depending on road type/speed etc

It used to take 40 miles to reach 80c prior to them being changed.

 

takes about 15 minutes, town driving, covering about 10 miles or so. never goes 91c. only if i'm stationary.

 

I've had the main thermostat replaced, by RA Engineering in Reading for a reasonable ?122 inlc vat coolant and parts. Engine now gets to 90-93 instead of 78ish. Looks like the main was a problem for me. With the engine cold I'll follow the exact same route as before and see what numbers I get. A drive around town suggests it'll be quite a bit better both to warm up and consumption. I must also get round to naming and shaming those dealers and independants who've looked at the car (well the computer) and not diagnosed the problem.

 

That is a very good price indead, well done.

The issue of the dealers not diagnosing the issue should be raised with BMW, in my opinion this all stems from the removal of the temp guage from the cluster in their newer cars. The old cars were great for letting you know that the stat had gone, the symptoms were clearly visible. However it is no excuse for the dealerships to not even take the thermostat off to inspect it. I was lucky with my dealer and being allowed to speak to the chief service tech, they replaced mine under warranty after confirming it was faulty.