Yes, definitely sounds like the main stat. When the temp got higher i'm betting you were in slow moving traffic, or stationary. Then as soon as you speed up the temp drops again due to the stat being stuck open. Did the heaters work ok when the temp was 90+?

Well now I turn the heaters off once I exceed 70kph. But I did try turn the heat up when temp rose, so long as I'm at low speeds or stationary (as you mentioned) heat was fine, speed up = no heat regardless of coolant temp. I'm going to have to wait for next week to get into this. Thanks for the help, good to have more people's input to put my mind at ease :thumbsup:
I'll keep you posted

How many bars is it supposed to show normally after warm? How do you access the hidden menu to see coolant temp? What is the right temp it should be when warm?

Bars on rev counter should be down to only 2-3 visible (for petrol, not sure on diesel). Here's a link on how to access the hidden menu:
KTMP is for the coolant temp. proper range is around 90 degrees Celsius, I wouldn't be worried if it's anywhere between 88-100 - It would move around a little due to driving conditions, but it shouldn't be far off this range.

I got the opposite problem..
 

Hi, my N52 is running on low coolant temp. Changed thermostat twice but no change. Its in the 76-85 deg with one exeption, in speeds > 95 km/h it heats up to 100-108 degC and seems to operate according to the N52 heat management design.

On throttle it cools down to 80 as per design to protect the cylinder heads.

Why on earth is it running on 80 deg in low speeds??

Can oil cooler be malfunction? Some other thermostat....

Thanks in advance

Torgny
Sweden

Hi Torgny, I'm having the same issues you are but mine doesn't heat up above 95kph... I would've thought it would run hotter at low speeds? I know mine does at the moment. From what I've searched most of them run too hot when thermostat goes bad, so ours are special cases :whistle:

are you referring to the oil cooler stat on the right of the radiator? I asked about that at the mechanic and he didn't think that would be related :hmm:
Unless you've got a diesel, which has an EGR thermostat (and some petrol 8 cylinder cars, I think), there aren't anymore thermostats. I would try changing the coolant temperature sensor (referred to as fan switch in some cases) it's cheap.
As soon as I've got news on any changes to mine I'll let you know:)

Many Thanks, yes it is driving me crazy. Its a BMW E61 Touring 2006 (N52 engine)

I logg ECU coolant via OBDII and app TorquePro.

Yes its the engine oil cooler that Ive heard have thermostats.

Its a bit disturbing that the BMW tech dont seems to know the heat management on this engine, it all started with fault code P0597 (thermostat bypass valve open) but it ran on quit good 95 degC, changed TS and it got "cold", changed again on complaints... same story still..cold.

Do you have any more specification on the coolant temp sensor (fan switch), art nr, link?

Thanks again I appreciate all help!

Chart engine coolant
 

See attachment! Engine Coolant driving on highway and city..between the "peaks, highway > 95 km/h" I stopped shortly and it heats up a little bit, then starting city driving gives the fluctuation 74-84 degC.

I recorded (via phone camera) sensor reading on dash today to show the fluctuations to my mechanic on Monday. I'm getting relatively the same readings you are, except above 95k there's no change still. When I stop, it's usually stable at 92.

Between the cars, they don't sound too far off in difference, mine's year older, N52 engine though so resolve one, resolve the others...
I know what you mean about not getting down to the bottom of it all even with BMW technician, change one part and all these other issues show up, nightmare :(

Since you say changing thermostat twice didn't resolve the issue, I'm thinking I should hold off pushing my mechanic for doing replacement and look for the cause elsewhere, really need Monday to hurry up so I can get some news, hopefully!

Part number for coolant temp sensor (fan switch) I got, 13621433077, no. 3 here: http://www.realoem.com/bmw/showparts...26&hg=17&fg=30
This is going in Monday as well.

have you changed the thermostat and/or checked the electrical connections to it (if it has them)? Petrols should run around 100C+ while doing 60mph , diesels 88C. The only way to check your thermostats are working is by checking what temp it holds while doing 50mph+